Skip to Content

Tutorial

Selective Color Boosting (Photoshop Tutorial)

|Tutorials|4 Comments

In this astrophotography image processing tutorial, I will explain an easy way to selectively boost the colors in your image. I like to call the technique “selective color boosting“.

Increasing the saturation of your deep-sky object can bring out the true beauty of your subject, and better showcase the contrasting elements of the nebula or galaxy.

The amount of “boosting” is up to you of course. Some prefer bright, vibrant colors, while others prefer a toned-down “natural” look. I’d like to consider my images to be somewhere in the middle. 

The definition of a “true-color” image varies, but the techniques described in this tutorial are generally accepted in the astrophotography realm. 

Selective Color Boosting for Astrophotography

The Triangulum Galaxy in RGB (Dedicated Astronomy Camera).

Long exposure astrophotography can reveal the colors of all deep-sky objects and galaxies. By exaggerating these colors through post-processing, we can increase the impact of the image.

In this tutorial, I’ll use Adobe Photoshop to accomplish our tasks. This software includes countless tools to perform the finishing touches on your images. (See the rest of the astronomy and astrophotography software I use).

I have also found it to be a fantastic start-to-finish image editor, with the help of a few third-party plugins of course. But we’ll get to that in a minute.

The example images in this article were captured using a variety of cameras, from an astro-modified DSLR camera to a monochrome CCD camera. The color boosting methods I describe will work for all color images, whether they are broadband RGB, LRGB, narrowband, bi-color, etc. 

The data used in this tutorial was registered, stacked, and calibrated in DeepSkyStacker first. If you need help with the pre-processing stages of deep-sky astrophotography, be sure to check out my premium image processing guide

For an overview of this process, please watch my video tutorial on YouTube:

How to Boost the Colors in Your Astrophotography Images

Astrophotography is a broad term and covers a wide variety of disciplines from wide-angle Milky Way nightscapes, to high-magnification planetary imaging. 

The methods of boosting color discussed below are most applicable to deep-sky imaging of nebulae and galaxies, but can also be applied to all forms of digital photography.

In a nutshell, you need to carefully isolate the areas of color that you wish to enhance, and leave the rest of the image alone. 

If you globally increase the saturation of your astrophoto, you run the risk of intensifying noise, color-mottling, and other nasty surprises hiding in your data. 

For example, in my image of the Whirlpool Galaxy shown below. I wanted to focus on boosting the colors of the areas of pink hydrogen inside of the spiral arms, without oversaturating the blue areas of the galaxy. 

whirlpool galaxy

The Whirlpool Galaxy in LRGB (Mono CCD and telescope).

The same selective color boosting method can be used on a wide-angle nightscape image too. The most challenging part of the process is the selection itself.

In the example image below, I again carefully isolated the areas of pink hydrogen emission nebulae. I was able to increase the saturation of these areas and brighten them with a careful mask selection. 

Truth be told, I could have done a better job at masking the darker areas of the night sky, but I think you get the idea. 

The Milky Way

The Core of the Milky Way. Canon DLSR and a wide-angle lens. 

As you can see, this technique gives you full control over the amount of saturation in your image in each area. The key concept is that you’re being very specific about which areas of color are boosted.

A basic saturation slider adjustment to the image as a whole will degrade the quality of your image significantly. 

With some inspiration to get your creative juices flowing, let’s get into the nuts and bolts of the process.

When to Start Boosting Colors

The timing of these actions on your image is up to you, but I highly recommend leaving it until the end. 

After the pre-processing stages (DeepSkyStacker, Astro Pixel Processor, etc.)

The first few steps you take towards processing your image should focus on balancing the RGB levels in the histogram and applying basic curve adjustments that bring up the signal.

Here is a basic image processing workflow timeline that I generally follow:

  1. Levels Adjustment
  2. Curves Adjustment
  3. Balance Levels
  4. Neutralize Background
  5. Curves Adjustment
  6. Star Color Adjustment
  7. Star Minimize
  8. Selective Color Boosting
  9. Noise Reduction
  10. Sharpening

You may want to make some less dramatic stretches to your colors along the way, but leave the selective color boosting method until the end of your workflow. 

The reason for this is that your image won’t be in a state that portrays what the final colors will look like until the end of your workflow. 

Soul Nebula

The Soul Nebula captured using a DSLR camera and a small refractor.

How to Select Specific Colors

There are two selection tools in Adobe Photoshop that allow you to isolate specific areas of your image. One (Color Range) makes an early, rough selection based on your input. The second (Select and Mask), is much more powerful and allows you to refine a detailed mask over your image.

With a careful selection and masking process, you can then create a new adjustment layer to increase saturation and vibrance. The same powerful masking technique also allows you to carefully adjust the highlights on your image, noise, sharpening, and much more.

In the image of the Pleiades shown below, I selected the outer nebulous regions of the object to increase saturation and bring up the midtones. 

new adjustment layer

At the heart of this image processing technique is the Color Range tool. This magnificent tool was introduced way back in Adobe Photoshop 3.0, and photographers have been enjoying it ever since. 

Select Color Range

The Color Range tool in Photoshop is an effective way to start the selection process. I like to use this tool to create a rough mask that can later be refined.

You can find this tool in the main menu under Select > Color Range…

select color range

The Color Range Tool is under the “Select” heading in the main menu.

This opens up a new dialogue box with a number of options to choose from. The drop-down menu at the top labeled “select” is where you will need to decide which method you would like to use to quickly grab the details you’re interested in.

I find “sampled colors” to be the most effective because you can use the eyedropper tool to manually point to the colors in your image you would like to enhance. 

The “highlights’ selection method is also very useful, as this is often the best way to separate your deep-sky subject (and stars) as a whole from a background sky.

sampled colors

“Sampled Colors” lets you manually pick the color range in your image.

No matter which selection method you use, you’ll want to do a basic refinement of your selection using the preview window. Make sure the “Selection” option is ticked during this stage.

In my image, I want to select the blue areas of the Trifid Nebula, so I can apply a targeted adjustment to this element only.

You simply need to click the eyedropper on the color range you would like to isolate, and the preview window will display a rough mask over these regions in the preview window. 

You can also change the selection preview dropdown menu to “Grayscale” for a live preview of your upcoming mask on your full-size image.

color range selection

The preview window provides a rough idea of your initial selection (change the selection preview to grayscale to see a full-size image).

You can adjust the “fuzziness” and “range” sliders to increase the selection of the mask. Make sure that you have the “localized color clusters” checkbox ticked off for full control. 

The eyedropper with the “+” and “-” icons next to them allows you to add or subtract from your selection, but they are a little too unrefined to be effective for our purposes.

The point of this step is to isolate the areas of color in your image that you wish to boost the colors in. Don’t worry about getting too specific at this point, as we will refine the mask substantially in the next step. 

When you are happy with your rough color range selection, you can click the OK button. Now you should see the “marching ants” selection on your original image, which is not a very helpful indication of our selection.

selection

Our initial color range selection is applied. 

The Select and Mask Tool

When it comes to processing astrophotography images, the Select and Mask tool is probably the most important tool in all of Photoshop. To really get the most out of your images, isolating one element from another is essential.

The Select and Mask tool allows you to refine your selections with an extremely robust set of adjustment options. Learning how to harness the power of this feature will most certainly improve your astrophotography image processing skills.

I will use the terms “selection” and “mask” interchangeably, as they are essentially the same thing. When we create a “layer mask” it just means that we are isolating a portion of the image to either be left-alone or targeted for adjustments.

With your original Color Range selection still active, navigate to the main menu, and click Select > Select and Mask

The Select and Mask tool. 

An important step to remember here is that you will want to make sure your original, rough, color range selection is active (as indicated by the marching ants on your image) before invoking the Select and Mask feature. 

There is a lot going on in the Select and Mask dialogue box. Below, I have provided an overview of the key adjustment sliders you’ll want to pay attention to when processing a deep-sky image. Click the image for a larger version. 

select and mask astrophotography

The purpose of this tool is to allow you to make precise refinements to your selection, and provide a clear indication of where this mask will be applied. 

There are several options to choose from when it comes to the way the mask is displayed on your image. The view modes are as follows:

  • Onion Skin
  • Marching Ants
  • Overlay
  • On Black 
  • On White
  • Black and White
  • On Layers

In my eyes, the Black and White view mode is by far the most useful. You may see the Onion Skin view mode appear by default, which I have found to be the second-best option from this list. 

Adjusting the Sliders to Refine Your Mask

The three most important sliders to adjust in the Select and Mask dialogue box are Contrast, Feather, and Shift Edges. A balanced approach between all three will yield the best results.

The Contrast slider is used to further separate your masked area from the rest of the image. With the Black and White view mode active, increasing the Contrast Slider will result in a more defined “shape” of the color range, with less of a transition area between the highlights and shadows.

Photoshop settings

The important adjustment sliders in the Select and Mask tool.

The Feather slider is the most important of them all because this creates a smooth transition between the edges of your mask and the background. Aim for super-soft edges around your targeted area to avoid harsh edges between your manipulated elements. 

The Shift-Edges slider is useful for expanding the area of your selection mask overall, retaining any feathering settings you have put in place. Between these three adjustment sliders, you should be able to create the ultimate layer mask for your image.

Note: You can use the brush tool (set to your desired width and softness) to remove specific areas of your selection. On a PC, just hold down the Alt key to subtract from the image when painting with the brush tool.

Accept the Mask and Create and a New Adjustment Layer

The default action that takes place after hitting OK on the dialogue box is to output to a selection. This will display the marching ants view overlay on your image. 

From here, you will want to create a new adjustment layer to apply your desired saturation boost and any other effects. For increasing color, you’ll want to choose the Vibrance… adjustment layer.

vibrance adjustment layer

The advantage of this procedure is being able to see a full-size preview of your image with your targeted adjustments to the selection happening in real-time. 

You may want to choose “output to: new layer“, as this will essentially accomplish the same result.

In this scenario, you would simply edit the new layer with your desired effects rather than as a new adjustment layer. 

Selective Color Boosting

By now you should have a solid understanding of how the color range selection tool works, and why it’s important to isolate the specific areas of your image that you want to manipulate.

With a well-defined selection mask placed over your image (remember, the white areas will be affected, the dark will not) you can begin to increase the vibrance and saturation of the important colors of your nebula or galaxy.

In case you’re getting a little lost in the order of things, here is a step-by-step path to get you up to speed:

  1. Select > Color Range
  2. Use Sampled Colors from Dropdown Menu
  3. Place the eyedropper on the color range you would like to boost
  4. Adjust the fuzziness and range sliders to roughly isolate these colors in the image
  5. Click OK to confirm your rough selection
  6. Open Select > Select and Mask to further refine your selection
  7. Use the Feather, Contrast, and Shift Edges sliders to create a smooth mask on your subject
  8. When you are happy with the selection (remember, no hard-edges!), click OK
  9. With the selection active, click Layer > New Adjustment Layer > Vibrance

The following illustration shows what your screen should look like at this stage. The new adjustment layer is the top-most layer, which ensures that your edits will be seen as you make adjustments. 

boost saturation

Adjust the vibrance and saturation sliders to your selected area.

Now, you can adjust the vibrance and saturation sliders to increase the color of your selected area. Pay close attention to your image at a glance at this stage.

Remember, drastic changes made to isolated areas of the image run the risk of looking unnatural. This is another reason why creating a mask with a soft, feathered edge is very important.

Any areas where the mask stops abruptly may appear odd in your final result. The more you “push” the data, the more pronounced this effect becomes. 

In the example below, I chose to increase the saturation of the warmer colors in the image. The Pinwheel Galaxy appears as a very cool blue color when stretched, and I wanted to contrast these cool areas with the warmer core of the galaxy. 

Pinwheel Galaxy

In this image of M101, Selective Color Boosting was used to keep the core warm, and the spiral arms cool.

There are no rules when it comes to the exact saturation settings you should use to enhance the color of your image.

I tend to bump the sliders up to about 15-20, depending on the deep-sky object, and the desired look I am going for. Once you are happy with the amount of boosting to the saturation and vibrance you have applied, you can simply close the properties window.

The new adjustment layer will sit on top of the other layers in your image. From here, you can save the file with the layers intact (.PSD file), or simply flatten the image and save it as a JPEG or TIFF. 

saturation settings

Typical vibrance and saturation settings for a deep-sky image.

Adjusting Color Balance, and Photo Filters

Since you have gone to the trouble of creating a highly selective layer mask, why not use it to make other color enhancements as well? 

In certain situations, creating a color balance adjustment layer is helpful. You can gently pull the colors towards a cooler or warmer result as desired. 

If bumping up the saturation and vibrance sliders don’t achieve the look you are going for, you can also try a specific photo filter

warming filter

The color balance and photo filter adjustment layers can be useful for certain looks.

I have found the warming filter to be useful for enhancing star colors, and the cooling filter to be useful for a natural background sky. In all scenarios, you’ll want to mask the area that you are applying the color filter to. 

Adjust the Opacity of the Adjustment Layer

Remember, you can always adjust the opacity of your new adjustment layer, and tone down the amount of saturation in your image.

If you feel like you have overdone it, just bring the opacity slider down to about 25%. Turn the layer visibility on and off to observe the subtle enhancement this technique makes to your astrophoto. 

I usually make my vibrance/saturation layer rather aggressive, and then bring the opacity slider down to about 50% to “normalize” things a little bit. 

You will have to practice the selective color boosting technique on a few images to really get a feel for it. The more types of images you perform this task on, the more comfortable you’ll feel.

Remember, this method can be useful for all types of astrophotography, not just deep space nebulae and galaxies. 

nightscape photography

Final Thoughts and Advice

If you were able to follow along with this tutorial, you should have a good feel for the Select and Mask tool, and its power. You can use the same selection process to perform other tasks on your image, from noise reduction to sharpening.

Although the examples in the tutorial focused on selective color boosting nebulae and galaxies, the technique works exceptionally well when processing star colors, too.

In this case, you would want to mask out the stars in the image on their own, so you have full control over their saturation without disrupting the rest of the image. 

For the wide-field view of the Eagle Nebula shown below, I isolated the stars using the “highlights” color range mode and increased their saturation independently from the rest of the image. 

star colors

The colorful stars surrounding the Eagle Nebula.

If you are unsure about how far to take your image, in terms of boosting saturation, I find it useful to use a reference image. I often search for APOD images of my target and see the direction that other amateur and professional astrophotographers have chosen to steer the image in.

If I could offer one more piece of advice, I would like to remind you why you began your journey in astrophotography: enjoyment. Adjust your personal images in whichever way you think looks best.

If you have found this image processing tutorial useful consider purchasing my premium astrophotography image processing guide

More Image Processing Tutorials:

Related Tags

Andromeda Galaxy Astrophotography Tutorial

|Galaxies|9 Comments

In this post, I’ll walk you through the image processing steps I used to create the image of the Andromeda Galaxy shown below. This astrophotography tutorial uses Adobe Photoshop to bring out the intense colors and detail of a galaxy that was photographed using a DSLR camera and a small telescope. 

You can follow along and process the exact same data I did (download here), or you can try these techniques on your version of the Andromeda Galaxy taken using your own equipment. If you choose to download my data and process it, you can skip straight to the Photoshop portion of this tutorial. 

This tutorial uses DeepSkyStacker and Adobe Photoshop. If you are new to this process, you may find the following DeepSkyStacker tutorial useful. The images used in this tutorial were captured using a Canon EOS 60Da DSLR camera with the RAW image type selected.

Messier 31 – The Andromeda Galaxy.

The equipment used for this shot:

telescope equipment

The camera and telescope equipment used for the photo on this page.

About the Image

This image was captured on a clear night under Bortle Scale Class 4 skies. A William Optics Zenithstar 73 telescope was used like a telephoto lens on my Canon DSLR camera. The telescope tracked the apparent movement of the night sky thanks to Sky-Watcher HEQ5 equatorial telescope mount. 

You can watch the complete journey leading up to this image in the following video: Photographing the Andromeda Galaxy. The images were collected while we camped under the stars on a beautiful August night. 

The final stacked image includes 67 x 2-minute exposures (2 Hours, 14 Minutes Total) at ISO 800. Calibration frames were used (15 x darks, flats, and bias) to help calibrate the final integration.

Wide-Field Version 

Roughly a month after capturing the original version of the Andromeda Galaxy shared on this page, I photographed this amazing object again from even darker skies. This time around, I used an ultra-wide-field refractor telescope, the William Optics RedCat 51.

The 250mm field of view at F/4.9 created the widest, deep image of the Andromeda Galaxy I’ve ever taken. Using the same image processing techniques shared on this page, I created the following image using 100 x 2-minute exposures with my Canon DSLR.

Andromeda Galaxy RedCat 51

The Andromeda Galaxy captured using the William Optics RedCat 51. 

I blended in my previous version of M31 using the Zenithstar 73, but only at about 25% opacity. I believe this helped to showcase a bit more of the outer structure details. 

Andromeda Galaxy Image Processing Tutorial

The goal of this image processing tutorial is not for you to follow my process step-by-step to achieve the same result, but to get a better understanding of the tools and techniques I use to edit my astrophotography images. No matter what level of experience you have, I am confident that you will find a number of helpful tricks you can use while processing your own image of the Andromeda Galaxy. 

before and after photo

Assessing your Data

After collecting your images of the Andromeda galaxy with your camera, you need to organize the all of the files on your computer so that you can easily find them. I like to sort all of the picture files and calibration frames into separate folders.

Create a folder for your light frames, dark frames, bias frames, and everyone’s favorite, flat frames. The root folder should include the date the images were taken so you have all of the information you need to reference later including the moon phase and location.

You may also want to include the telescope, camera, and filter that were used in the folder name, as these details may be hard to remember years later. Here is a look at the folder structure for my data on the Andromeda Galaxy.

folder structure

Make your life easier by taking the time to organize your images and calibration frames into folders.

You may find it useful to go through your light frames in a RAW image preview software such as Adobe Lightroom or Adobe Bridge. Delete any frames that have airplanes, or satellites passing through them, or that are not the full exposure length. If your tracking accuracy and autoguiding were successful, you should not have to delete any frames due to poor tracking. 

With the files organized and easy to find, we can now import the image data into DeepSkyStacker for calibration and integration. This will create an intermediate file that can then be processed extensively in Adobe Photoshop. 

Stacking and Calibration

DeepSkyStacker will allow us to calibrate our data using support frames, and improve the signal-to-noise ratio of the final image through integration. The software will automatically align and register the images on top of one another, to reduce noise and increase the signal (light) in the image.

To start, select all of your light frames (the actual pictures) by clicking the Open picture files button on the top left of the screen. This is where you will choose all of the images on the Andromeda Galaxy you would like to stack. If you have organized your images and folders neatly, and have filtered out any images that should not be in there, this process will be very easy. 

deepskystacker

Load all of your light frames (picture files) into DeepSkyStacker.

You will then need to repeat the process, for your calibration frames. Click on the buttons for dark frames, flat frames, and bias frames in the top left-hand menu of DeepSkyStacker. I recommend using at least 15 support frames to properly calibrate the image for further processing. 

You can review the details of your image files in the lower portion of the screen.

This is a great time to check to make sure the following:

  • Your light frames are all the same exposure length and ISO
  • Your dark frames match the exposure length and ISO of your lights
  • Your Bias frames are the fastest exposure length possible
  • You have loaded at least 15 flat frames into DeepSkyStacker

image stacking

Review the details of your image files in the lower half of the DeepSkyStacker dashboard.

If everything looks in order, you can go ahead and click check all, followed by Register checked pictures. From here, we will need to make sure that a few key settings are used so that DeepSkyStacker can properly integrate and calibrate the image data. 

Register and Stacking Settings

Use the Register Settings shown in the image below as a reference. Because we have used all of the recommended calibration frames, and have pre-screened the images, these settings should work well. Feel free to try using the exact settings I have used to stack the image, including the sigma-clipping combination method to stack the light frames. 

deepskystacker settings

Recommended Settings in DeepSkyStacker.

You can change the Star detection threshold in the advanced tab of the Register Settings. The setting you use will depend on the type of data you are stacking. For this image, I suggest using a threshold of 25%, as it will speed up the stacking process significantly, and 456 stars are more than enough to successfully register the image. I have always kept the “Reduce the noise by using a Median Filter” option checked. 

star detection threshold

As for the Stacking Parameters (which can be accessed by clicking the button in the Register Settings box), I suggest leaving the default settings in place under the light, dark, flat, and bias tabs. You can select the Enable 2x Drizzle option if you want, but be warned that your computer will kick into overdrive, and the output file will be massive. (learn more about the benefits of using drizzle). 

stacking parameters

Now, click the OK button and review the final Stacking Steps of your image, and the estimated total exposure time. The total integrated exposure time for my image of the Andromeda Galaxy is 2 hours, and 14 minutes. 

Your stacked image of the Andromeda Galaxy may look very different than mine. Everything from the amount of exposure time invested in the image, to the filter used will affect this. 

The resulting image of the Andromeda Galaxy shown below has a typical look to broadband, color images shot using my DSLR camera. This is our intermediate file, that is now calibrated to reduce much of the noise and artifacts present in a single exposure. 

astrophotography image

The stacked 32-Bit TIF file created by DeepSkyStacker.

The integrated data now has a much better signal-to-noise ratio, which will make the processing and manipulation techniques in Adobe Photoshop much more effective. The final processed image will look much different than the version you see at this stage.

Image Processing in Adobe Photoshop

Adobe Photoshop is powerful tool for processing astrophotography images. It is a robust graphics software designed primarily for photography and design, but many amateur (and professional) astrophotographers use Photoshop for astrophotography image processing. 

Adobe offers a subscription service for their complete Creative Cloud Suite, or for stand-alone products such as Adobe Lightroom or Photoshop.

Adobe Photoshop CC

Download Photoshop CC (Single App Plan)

Open the Stacked TIF Image

The first thing we need to do is open the file that DeepSkyStacker created using all of our pictures and calibration data. By default, DeepSkyStacker will output the intermediate file as a 32-bit .TIF, in the destination you have selected in the settings.

The default name of this file will be Autosave.TIF. You can change this file location in the output tab of the stacking settings option.

Alternatively, you can save the stacked .TIF file by clicking Save picture to file, at which point it will convert the image to 16-bit mode. We need to convert the 32-bit image to 16-bit to fully process the file in Adobe Photoshop anyway.

Now it’s time to open the TIF file you created in Adobe Photoshop. If you are opening the Autosave.TIF file that DeepSkyStacker created on it’s own, you first need to convert the image to 16-bit, by clicking Image > Mode > 16-Bits/Channel.

You will now have complete access to all of Photoshop’s tools to manipulate the data.

Crop and Initial Curve Stretch

I like to start by cropping the image slightly, just enough to remove any stacking artifacts around the edges of the image. This can create an inaccurate histogram reading, and you wouldn’t want to include these edges in your final image. You can use the Crop tool, or simply select the area you would like to keep (98% of the image), and click Image > Crop from the main menu. 

The first change we will make to the data is a simple curves stretch. Using the Curves tool (Image > Adjustments > Curves), perform a basic curve stretch using the image below as a reference. Now, the data is non-linear, and has been manipulated to help us better see the dynamic range of this object. All of the amazing deep sky astrophotography images you have ever seen were “stretched” like this. 

curves stretch

My initial curves adjustment.

For this object, it is important that we do not over-stretch the core of the Andromeda Galaxy. It is the brightest area of the object, and details surrounding it could easily be lost. To avoid this, you can either blend in shorter exposure images of the core using a layer mask, or isolate this area (again, using a mask) so that you do not stretch this data as far as the surrounding details.

In the next step, I’ll show you an easy way to selectively stretch all of the areas of the image except the bright core. 

Selective Curve Stretch

To start, we’ll select the brightest area of the image using a mask. Click on Select > Color Range > Sampled Colors. Now, use the eyedropper tool within the Color Range dialog box to select the nucleus of the Andromeda Galaxy. 

Feel free to use settings similar to the ones below on your image. This will create a rough mask that we now need to refine.

color range

Now, navigate over to the Select and Mask tool (Select > Select and Mask) to soften the edges around the selection. This is an important step, because we need to create a smooth transition between the areas at the edges of the mask. 

Once you are happy with the amount of feathering around the mask (using the Feather slider in the Select and Mask dialog box), you can click OK, and the selection mask will activate. Now that we have defined the area we want to leave untouched, we need to click Select > Inverse to apply our curves adjustment to. 

Perform a modest curves stretch as you did in the last step, and notice that the areas we have masked off (the nucleus of the Andromeda Galaxy) remain unchanged. You may want to make several iterations of this process, making small curves stretches each time. 

Before/After

Before and after making a selective curves adjustment. 

If you were too aggressive in your selective curve stretch, you will create an unnatural looking transition between the core of the galaxy and the mid-tone areas. To avoid this, find a balance between the amount of feathering at the edges of your mask and the amount of curve adjustments you make. 

The same process of masking the bright core of the galaxy can be used on the surrounding stars in the image. This technique is a great way to pull your data forward without bloating the stars. 

Color Balance the Image 

At this stage we will balance the color of the image by setting the black point, and the white balance. Start by creating a Threshold Adjustment Layer (Layer > New Adjustment Layer > Threshold). This creates an exaggerated view of the image showcasing the brightest and darkest areas of the image.

Threshold Adjustment Layer

A threshold adjustment layer used for setting the black and white points. 

We’ll use this layer to plot our black and white prints of the image. The black point is used to balance the background night sky to a neutral grey, while the white point is used to set a natural white color as we know it on Earth from the Sun. 

Using the slider in the properties tab of the threshold adjustment layer, choose an area of the sky that contains no stars, and is not touching the galaxy. Use the Color Sample Tool (found in the main toolbar) to plot 2 points on the image where there is nothing but dark sky.

Make sure that the Sample Size (found at the top left of the screen) is set to 5 by 5 average for the best results. 

Setting the Black and White Points

Now, plot a point on the image that is the brightest “white” area of the picture. In most cases, this is a star, but this time I have chosen to use the center of the galaxy core to set the white balance. For the most accurate rendition of colors, you will want to use a star that is the same type (G2V class) as our Sun.

These plotted points will now give us a reading of the pixel information and the current balance of colors in the image. To see this information, turn off (or delete) the threshold adjustment layer, and open the Info window (Window > Info).  

At this stage, we just need to balance the colors out a bit. If your image is like mine, it is very brown and ugly at the moment. We can balance the colors by adjusting each color channel independently and matching the values of our plotted points.

With the Info window open, click on Image > Adjustments > Levels. From the levels window, select each color channel from the drop-down menu and adjust the sliders. For my first levels adjustment, I have set the black point to read 20, 20, 20 across the RGB channels. These values will increase shortly, as we will pull the data forward even more. 

color balance

This is a good time to save the image. For all further edits, it is wise to create new layers on top of the original. This way, you can save the file with each adjustment made on its own layer. Label each layer with the adjustment you have made, and then you can save the complete .PSD file with the ability to go back and edit at any stage later. 

Targeted Curves Adjustment 

A powerful way to make a targeted curves adjustment in Adobe Photoshop is to hold down CTRL on your keyboard and plot a temporary reference point. With the Curves window open, hold down CTRL and click an area of the background sky. Now, holding down CTRL once more, click an area of the Andromeda Galaxy that you would like to brighten (the mid-tones at the edges of the galaxy),

If you noticed, the histogram on the Curves window now has two points plotted on the graph. You can now “pull” at the data with a targeted approach, as you now know where specific pixel data lies in the graph. The goal is to bring out the mid-tones, without bringing up the dark sky, or disturbing the bright core of the galaxy.

Curves Photoshop

Making a curves adjustment with plotted points on the histogram. 

At this stage, we can now see a lot more of the galaxy structure. The image is far from done, but it’s nice to see all of the interesting details of our deep sky object. This is another great time to save the image. I also like to use the History state feature of Adobe Photoshop (Window > History) if I ever need to go back and make small changes during my process.

Saturation Boost

You may want to increase the saturation of the colors in your image (watch my video tutorial on boosting colors). I find the best way to accomplish this is to create a Hue/Saturation Adjustment Layer. We need to define specific areas of the image to apply this effect to, and the Color Range Tool is a convenient option. 

Go to Select > Color Range > Highlights, and adjust the slider to define the areas of light we would like to increase the color of. In my case, I have chosen the bulk of the highlights, as I would like to increase the saturation of the galaxy as a whole, and the brightest stars in the field.

To refine the selection, you can use the Select and Mask Tool, or simply Select > Modify > Feather using a value of 1 or 2. 

With the selection active, go to Layer > New Adjustment Layer > Hue Saturation. Now you can adjust the Saturation slider to taste, boosting the intensity of the colors in your image. This is where your personal taste dictates the direction of the image. I would suggest not going overboard with your saturation boost adjustment. 

At this point, I recommend creating a visual merge (Shift + Ctrl + Alt + N + Eon the keyboard), and naming this layer “SATURATION”. If you have followed a similar path to me, your image and layers will look a little something like this:

Andromeda Galaxy Photoshop Tutorial

The Andromeda Galaxy with a selective boost in saturation. 

If you want to dive deeper into this process, you can read my full tutorial on selective color boosting for a complete breakdown of the technique.

Minimize Stars

Minimizing the size of the stars in your image is a great way to draw more attention to your deep-sky object. I find it to be one of the most dramatic differences between a good astrophotography image, and a great one. 

Reducing the size of the stars in your image is easy, but you will need to monitor a few things along the way. First, create a new layer, and name it STAR MINIMIZE. That way, we can turn the layer on and off to see the difference it made. 

Start by using the Color Range Tool again, selecting Highlights from the drop-down menu. Adjust the slider so that most of the stars are selected, but not the entire disc of the galaxy.

The goal is to select only the stars, so we can apply a minimizing effect on them. We will need to refine this selection and remove the bright areas of the galaxy, as we want these areas to remain unchanged. 

Using the Lasso Tool (found in the main toolbar), hold down the ALT key, and draw around the areas of the Andromeda Galaxy that you do not want to apply a star minimizing effect to. Holding ALT will ensure that this action de-selects area of the selection. 

star minimize

Settings for minimizing stars with the minimum filter in Adobe Photoshop. 

Now, go to Select > Modify > Expand, and expand the selection by 1 pixel. You should notice that the “marching ant” selection has changed and that there is now more room around the star selected. You may want to expand the selection by 1 more pixel, depending on the aggressiveness of the original selection made.

Next, go to Select > Modify > Feather, and use a Feather Radius of 1 pixel. This has softened up the selection around the edges, which is important for blending purposes. 

With our selection carefully refined, we can apply the star minimizing effect to the stars. Go to Filter > Other > Minimum, and use a radius of 1.0 pixels. Make sure that the Preserve option is set to Roundness and click OK. Click anywhere on the selection using the Lasso Tool to deselect it. 

Here is what my image of the Andromeda Galaxy now looks like with smaller stars.

Smaller Stars

Noise Reduction and Artifact Removal

If your stacked image includes 3+ hours worth of exposure time, chances are the noise is minimal. For my data, there is still quite a but of camera noise in the images, even using 67 light frames and calibration data. There is also an unnatural glow coming from the bottom of the image.

Let’s start with the noise. I prefer to use the noise reduction tool found within Adobe Camera Raw. To access this feature, click Filter > Camera Raw Filter. The noise reduction tool is found under the Detail Tab and can be controlled using the Luminance slider under the Noise Reduction heading. 

Zoom into the image to about 200%, and experiment using different levels of noise reduction on the slider. You can also mask and sharpen the image using this tool, but I don’t recommend doing that yet (even though I did in the example). Here are the noise reduction settings I chose to use for my image of Andromeda. 

noise reduction settings

Use the sharpening tool found under the detail tab of Adobe Camera Raw. 

Now that the noise is under control, we can tackle the subtle glow at the bottom of the image. In this situation, I think the easiest way to correct this is by copying the top most layer, and reducing the brightness. Then, I can remove the areas of the image that I do not want to darken using a simple mask and the Eraser Tool

Odd gradients like this are some of the most challenging processing scenarios, and can usually be avoided with proper flat frame calibration. I’m not quite sure what went wrong this time (the horizontal banding indicates it could be something to do with the dark or bias frame signal), but luckily fixing a subtle horizontal gradient like this is not too difficult. 

Gradient Xterminator is a handy third-party plugin for removing gradients and vignetting in your images. This is the method I used on the Andromeda Galaxy image, although I have shared ways to remove gradients without Gradient Xterminator in the past. 

Using Photoshop Actions

I have installed a useful astrophotography image process Action Set to my version of Adobe Photoshop, and I find it exceptionally useful. The Astronomy Tools Action Set contains many time-saving, powerful actions you can apply to your image with the click of a button. You do not need these actions to create amazing images in Photoshop, but I find them to be very handy.

If you are using this action set, I like to run the “Enhance DSO and Reduce Stars” action at this point. It can make a dramatic difference to the image in a single click. It basically pulls the faint details of the galaxy forward and applies another star minimizing effect the image. I prefer to set this layer to 50% opacity once complete.

You can also try running the “Make Stars Smaller” action, which should be used carefully as it can eat away at the stars in your image. 

Here is a look at each layer of the process, to give you a clear idea of when each processing technique took place.

processing steps

Each layer of the image is labeled with the processing step that took place. 

Selective Sharpening

It is wise to only sharpen the areas of your images that you intend to sharpen and to not simply run a sharpen filter over the entire image. For example, you would not want to sharpen empty areas of the background sky or the larger stars with a pleasingly soft glow. 

Again, we’ll use a mask selection to isolate the areas we would like to sharpen. The Select > Color Range > Highlights method works well, and be sure to refine the mask with careful feathering.

The sharpening filter I enjoy most is the one found inside of Adobe Camera Raw. This tool features a number of useful options to apply just the right amount of crispiness to your image. You’ll find it under the Detail Tab of Adobe Camera Raw (Filter > Camera Raw Filter).

Andromeda Galaxy

Finishing Touches

From this point forward, you need to decide the overall story you want to tell with the image. You can apply subtle tweaks to enhance the details of the image you enjoy most, whether that is having tiny stars across the field, cool blues in the galaxy, or a well-defined core. It may take several astrophotography image processing sessions to understand what makes a great image in your eyes. 

You may want to adjust the orientation of the image, too. For the Andromeda Galaxy, I like to see it in portrait orientation so the galaxy is on an angle. To me, this gives the Andromeda Galaxy more depth and better showcases its spiral structure.

One tip I’d like to share is to process two entirely different versions of the image. This means starting from scratch, making subtly different decisions about each action along the way. Then, compare both processes of the image, and decide which one you like best. Often times, I will combine the two processed image together with the top layer at 50%. 

With the selective masking techniques I shared in this tutorial, you’ll have countless ways to process your image of the Andromeda Galaxy in the fashion that you prefer. 

astrophotography

I hope you have enjoyed this image processing tutorial on the Andromeda Galaxy. To keep up with my latest videos, tutorials, and equipment reviews, please subscribe to the AstroBackyard Newsletter

Download My Image Processing Guide

If you would like to learn about every astrophotography image processing technique I use in DeepSkyStacker and Photoshop, you can download my premium guide. The PDF download contains over 100 pages of the specific steps I take to process all of my images. The guide is available here.

image processing guide

Related Posts:

Related Tags

Use the Select and Mask Tool in Photoshop

|Tutorials|3 Comments

The Select and Mask Tool in Photoshop CC is a powerful way to edit selective areas of your astrophotography images. Whether you want to separate the stars from your deep-sky target, or apply subtle noise reduction to the background sky of your image, the select and mask feature will get you there.

Adobe Photoshop CC is an effective way to process astrophotography images, in a very creative and enjoyable way. If you use Photoshop to process your astrophotos as I do, this tutorial should be very useful to you.

Adobe Photoshop CC

Download Photoshop CC (Single App Plan)

About a year ago, I experienced the true power of the Select and Mask tool in Photoshop first hand. It has quickly become one of my favorite and most-used features of this application for processing my deep sky astrophotography images.

The Select and Mask tool allows you to get very specific about each and every edit you make to your images. Creating layer masks is one of Photoshop’s core features, and it is especially useful when editing astrophotography images. 

Photoshop Tutorial

The Select and Mask Tool

The Select and Mask tool is Adobe Photoshop’s powerful selection tool with advanced mask refinement options. It gives you complete control over your layer mask and allows you to precisely define the edges of your selection.

When processing a deep sky astrophotography image, it is often beneficial to select different aspects of your images and process them independently from one another. For example, there are times when you will want to increase the brightness of a nebula, without bloating the stars in your image.

When selecting these areas to process, you want to avoid creating a hard, unnatural edge between your selective area and the original. For this reason, being able to accurately feather your selection allows you to control the amount of softness between these areas and naturally blend them together.

In the example below, you’ll see how I have increased the saturation of the Lagoon Nebula, without adding color noise to the background sky or stars.

By using the Select and Mask tool to define the colors found in your deep-sky target,  you have complete control over the amount of saturation applied. By using the selection mask as a reference, you can confirm that you are only applying these effects to the nebula, and not the image as a whole.

Where to Find the Select and Mask Tool

Those that are using the latest version of Adobe Photoshop can navigate to the Select and Mask tool from the Main Menu Bar in a few ways. The most direct route to this feature is:

Select > Select and Mask

This is the path most people will take that are using the Select and Mask for general photography purposes, but not necessarily astrophotography. Here, you’ll find tools such as the Quick Selection Tool and the Refine Edge Brush.

These features are useful for accurately masking a subject and removing them/including them on a new background. The Onion Skin view mode is particularly useful here, as it adjusts the opacity to provide you with a useful view of both layers at a time. 

Although this is a “one-stop’ shop” for refining your mask selection, I don’t consider it to be the best way to utilize this tool for astrophotography image processing purposes. Instead, I prefer to start with the following path:

1. Select > Color Range

To start, use the traditional method of making your selection based on my original image processing workflow. This will give us a rough selection to start with, that we can refine further using the Select and Mask tool. 

In the example below, I used the Sampled Colors option in the “Select” drop-down menu. When making a selective increase to color saturation, it’s often best to sample the dominant colors of your deep-sky object.

You can also use the Highlights selection mode, and adjust the Fuzziness slider to include the areas of light (signal) in your image. Keep in mind, this method will usually include your stars, as well as your deep-sky target. In many cases, you will want to separate the selections between the two. 

Select color range tool in Photoshop

With the “Marching Ants” now showing (the dotted lines that Photoshop uses to indicate a selection), we can now refine our selection mask by navigating the Select and Mask button in the Select drop-down menu.

I cover this topic in-depth in my detailed selective color boosting tutorial.

2. Select > Select and Mask

Here is where things get interesting. I suggest using the Black and White view mode, as it is the most helpful masking overlay for our purposes. The black areas of the image are un-selected, while the white areas are where we will isolate our adjustments to.

By far, the most powerful refinement tool here is the Feather slider. This is where we can adjust the amount of blending refinement between our subject and the rest of the image.

The Select and Mask Tool

Feel free to adjust the Radius slider in the Edge Detection area if desired, although I usually leave this slider alone personally. You may find the Smooth slider found underneath the Global Refinements heading to be useful as well.

The great thing about the Select and Mask feature is the ability to preview changes made to your layer mask in real-time. You can adjust the sliders on the right, and monitor how these changes affect your selection before activating the selection.  

I recommend only adjusting the Feather and Shift Edges sliders under the Global Refinements heading to start. In my opinion, these two adjustments have the biggest overall impact on the usefulness of your selection when it comes to astrophotography.

Shift Edges will expand your selection to include even more of your original selection (your subject). In turn, you are also selecting more of the image overall, and becoming less selective about where you will apply edits to. 

Feather will increase the softness of your selection at the edges, creating a smoother, more natural blend between the areas you enhance and the rest of your image. I believe that the true value of the Select and Mask tool lies in this feature alone. 

Refine your selection using feather

As you can see, you’ve got some decisions to make here. I suggest using a middle ground between the examples above. Here are the exact settings I used to select the Omega Nebula in my example.

selection settings

Applying Effects to Your Selection

The whole point of spending so much time and effort refining our selection is to make powerful adjustments to the selection from increasing saturation to sharpness. Having the ability to make accurate selections that will blend seamlessly into the original image is an incredibly powerful tool.

Any adjustments made to the selection can then be isolated and organized in its own layer, and the level of opacity can be adjusted to taste. Slowly applying subtle enhancements to your image in a very intentional and responsible way can lead to some incredibly powerful images. 

Some of the primary adjustments I apply to selected areas of my astrophotography images include:

  • Saturation Increase
  • Noise Reduction
  • Sharpening
  • Star Minimizing

All of these enhancements can be made to specific aspects of the image in an organized way. This technique ensures that you do not apply enhancements in one area, that degrade the image in another. For example, you can apply a stronger level of noise reduction to the areas of your background sky, while leaving the delicate sharpness of details within your deep-sky object intact. 

An example of this technique in practice when using a third-party plugin like Topaz DeNoise AI to reduce the noise in your image. Although this took benefits from machine learning and largely understands which areas of the image to “leave alone”, you’ll still want to protect the critical regions of detail in the image using a layer mask before running the tool. 

Use it to Create New Adjustment Layers

The Select and Mask tool is best utilized when in combination with an adjustment layer. Adjustment layers are a key element of a non-destructive image processing workflow, as they allow you to go back and make changes to the layer.

One example of an effective adjustment layer is one that sharpens the fine details of your subject, yet does not sharpen the background noise, stars, or any other aspect you do not wish to sharpen.

You can use the Select and Mask tool to isolate the areas of your image you want to sharpen, and feather the edges of your mask to blend the affected area into the background sky.

Use the advanced mask refinement tools to target your area of interest, and apply your sharpening adjustments using the Adobe Camera Raw filter.

New Adjustment Layer

By applying the sharpening enhancements to an isolated area, you can sleep comfortably knowing that you have not degraded the quality of your starry background sky.

The same process can be applied to image enhancements such as increasing star color, correcting gradients, and many more useful image processing tasks.

I hope that this tutorial has inspired you to try the valuable Select and Mask tool found within Adobe Photoshop CC. For my latest updates, tutorials, and reviews, please subscribe to the AstroBackyard Newsletter

Photoshop image processing tutorial

Interesting Note:

The photo of the Lagoon Nebula above (and in the video) was captured using amateur, affordable astrophotography gear back in 2013. It is possible to photograph incredible deep sky objects in space using an ordinary DSLR camera and small telescope with the right approach.  Here is a breakdown of the equipment used for this photo:

astrophotography telescope

The Explore Scientific ED80 Triplet APO Refractor.

Download My Image Processing Guide

If you would like to learn about every astrophotography image processing technique I use in DeepSkyStacker and Photoshop, you can download my premium guide. The PDF download contains over 100 pages of the specific steps I take to process all of my images:

image processing guide

Related Posts:

Related Tags

Deep Sky Astrophotography Step-by-Step Walkthrough

|Tutorials|13 Comments

In this post, I’ll break down everything you need for deep sky astrophotography with a telescope. I’ll cover each piece of gear I use, and explain how it can be used to capture beautiful deep-sky images of space from your backyard.

Deep-sky astrophotography is a rewarding and fulfilling hobby, especially once you’re able to achieve impressive results from your own home. This post aims to give beginners a better idea of what you need, and what you can expect to accomplish yourself.

I’ll be setting up from scratch, and talk about each piece of gear used, so you can replicate my process. I’ll warn you right now my methods are by no means “the right” way to do this, it’s just the way that works for me.

Deep Sky Astrophotography Walkthrough

The following video takes you through my current deep-sky astrophotography routine step-by-step. For a more detailed description of the process, keep reading!

First things first, if you’re brand new to deep sky astrophotography, here’s how it works. I use a tracking equatorial telescope mount to compensate for the rotation of the Earth. Because the night sky slowly rotates throughout the night, we need to “freeze” the sky in place in order to capture a long exposure image.

A long exposure photo of 1-minute or more will collect much more light on an object in space than you could ever see with your naked eye alone. This detail is collected onto the camera sensor, and can then be processed to pull out even more color and detail.

Elephant's Trunk Nebula

The Elephant’s Trunk Nebula in Cepheus.

When it comes to deep-sky astrophotography, you can consider the telescope to act as the camera lens. The focal length and aperture offer you the power needed to get a close-up look of some incredible deep-sky objects in space. In general, the most important aspect of deep-sky astrophotography is to collect as much data as possible – good data.

It needs to be sharp, well-exposed, and well framed. With good data, the image processing stage is a lot of fun. With enough overall exposure time, your image will benefit from a strong signal-to-noise ratio.

You can learn more about the basics of deep-sky astrophotography in the “get started” section of this website. For now, I’ll focus on what you need to start capturing quality data from home.

deep sky astrophotography walkthrough

Before Getting Started

The last thing you want to do is spend time carefully setting up all of your gear on a night when the weather forecast is not promising. I usually don’t set up my equipment unless I am confident the sky will be clear until dawn. I monitor a variety of weather forecasting apps to see if the sky will be clear during the night from my location.

clear outside

I have found that the most accurate tool to forecast a clear night sky is Clear Outside by First Light Optics. I use the Android app version on my smartphone. The app includes several useful metrics including visibility, wind direction, estimated sky quality and more. I like the low, med, high cloud format and have found it to be astronishly accurate.

The Clear Sky Chart is another great tool to use, but I find the forecast to be a little optimistic for the most part. Often times, the forecast looks better on the clear sky chart than it does on Clear Outside. This tool is an online webpage rather than an app, but it has an impressive amount of locations across the world listed. Just Google your location + clear sky chart.

Step 1: Powering the Gear

We need to power the equipment, so I usually run an extension cord (or two) out to my imaging location in the backyard. Many people use a portable battery pack to power their gear, and so do I when I don’t have access to electricity.

You can save some serious cash by building your own battery pack using a deep-cycle marine battery and an inverter. I bought one of those battery booster packs from the hardware store for convenience – but they don’t last long and are overpriced.

The model I use is a Motomaster Eliminator 600W (Similar to this style) and it has enough juice to power all of my equipment for 1 night. After that, it’ll need another full charge to reliably go another night. I’ve had batteries die on me in the past, and it’s a heartbreaking moment.

Step 2: Level the Tripod Mount

An astrophotography telescope mount must sit on a tripod, or in my case a tri-pier. A rock-solid base for the equatorial tracking head of the mount is essential. You’ll need to confirm that it is level and secure to avoid headaches later on.

Equatorial Mount

Many people build a custom concrete pier and fasten their tracking mount to it for the ultimate stable platform. This, of course, requires a permanent spot for your equipment. I’ve thought about constructing a small observatory in my yard, but I’ve decided to wait until I have a little more property to work with.

No matter what size of tripod or pier you use for astrophotography, you need to make sure that it won’t slip or move throughout the night.

Step 3: An Equatorial Mount

Many astrophotography mounts include a built-in bubble level, which comes in really handy if you often set up in new locations. For the current mount that I use, I simply adjust the length of the tri-pier legs until the mount head is as level as possible.

The astrophotography mount I currently use is an iOptron CEM60, which was generously loaned to me from Ontario Telescope and Accessories. It’s a center-balanced equatorial mount that uses a magnetic gear system.

iOptron CEM60

The mount moves the telescope in 2 axes, right ascension (RA) and declination (Dec). It allows me to point at any deep sky object that isn’t obstructed by trees or houses in my backyard.

Once it’s centered on the object, it will track it and keep it completely still so I can photograph it. (Autoguiding improves this, but I’ll cover that momentarily) The iOptron CEM60 is a GoTo mount, which means that I can enter the target name into the keypad, and then the mount will slew the telescope to it for me.

Recommended Telescope Mount Options:

 

telescope mounts

Entry Level: Orion Sirius EQ-G Computerized Telescope Mount

Intermediate: iOptron CEM60 Center-Balanced Equatorial Telescope Mount

Professional: Software Bisque Paramount ME II

Step 4: Polar Alignment

Accurate polar alignment is crucial for a successful deep-sky astrophotography image. The process of polar-aligning a telescope mount for astrophotography may sound difficult to achieve at first, but it’s really not that complicated.

The reason I mention it at this stage is that you’ll need to roughly have your telescope mount polar aligned when setting it up. Meaning, the counterweight shaft should be pointing directly north. Because I am in the northern hemisphere, I use Polaris, the north star, as a guide to accurately polar align the mount.

polar alignment

If you live in the southern hemisphere, or can’t see Polaris, there are alternative ways to polar align. Software assisted methods such as drift alignment can help. I’ve used a polar alignment routine in a program called SharpCap. PHD2 guiding (which ill cover shortly), also has a useful drift alignment tool.

The way I do it, is to use a simple app on my phone (PolarFinder) to tell me exactly where Polaris needs to be in my polar finder scope to be polar aligned from my location. It uses my GPS coordinates and places the star in the correct position for my exact location and the current time.

Then, it’s just a matter of matching up what the app tells me on the mount by adjusting the alt-az knobs. The entire process should only take about 2 minutes once you are used to it. If you’re really not interested in this manual process, or can’t see Polaris. You should probably check out the QHY PoleMaster.

polemaster polar alignment

Using the QHY PoleMaster to accurately polar align my telescope mount.

Step 5: Balancing the Telescope

Now that we’re polar aligned, we can get to the fun part – mounting the astrophotography telescope. Along with being polar aligned, balance is a major factor to consider when setting up your rig.

All equatorial mounts include a counterweight, which I’ll need to use to balance this 20-pound refractor telescope. You need to balance the scope in both axes so that the mount doesn’t have to work any harder than it needs to when slewing and tracking objects in the night sky.

astrophotography how to

The telescope I’ll be using is a William Optics Fluorostar 132. It’s an apochromatic triplet refractor, which is one of the best telescope types to use for the purposes of astrophotography. It has a focal length of 925mm and an f-ratio of F/7.

A telescope like this has enough aperture to pull in some serious light and get an up-close look at some of the most impressive deep-sky nebulae.

We need to attach the imaging payload (the camera) to the telescope, along with the autoguiding system for an accurate overall weight to balance. This is the payload that will need to be tracking smoothly while the photos are being taken. Even the distance the focuser is from the tube will make a difference in the balance, so there may be some trial and error here.

The closer your imaging payload is to the maximum capacity of your mount – the more balance comes into play. For reference, the CEM60’s 60-pound payload capacity is very forgiving with my relatively light 25 lb imaging gear.

In general, your mounts payload capacity should ideally be double the weight of your astrophotography gear. This may seem excessive, but long focal lengths and long exposures demand the greatest of tracking accuracy. If you haven’t taken the time to balance your telescope, even the slightest imbalance may come back to haunt you over time.

Step 6: The Imaging laptop

There have never been so many great options for controlling your camera or mount remotely for astrophotography than there are now.

Dedicated astrophotography computers, mini pcs, and good old-fashioned laptops. I’ve been using the same laptop since I started taking images of space back in 2011. It runs Windows 7, and all of the astrophotography software needed to run a successful imaging session.

laptop computer

The Astrophotography Software I Use:

The computer has software installed for controlling the camera, the mount and of course an internet connection. I can remote into this laptop from in the house using Team Viewwe to check up on things from inside the house.

Step 7: Autoguiding Setup

Now, let’s talk about this smaller telescope riding atop the big one. This is called a “guide scope”, and its job is to help the mount track with even greater precision.

I’ll attach a small camera into this telescope, which will feed an image to my computer with a looping image of stars. Then, my computer will communicate with the mount to make small adjustments in periodic error for improved tracking accuracy.

autoguiding

It sends guide pulses to the mount to based on the tiny movements it read from the guide star. This is called autoguiding, and it can be the difference between the ability to capture a 30-second exposure and a 5-minute exposure.

For my upcoming task of star alignment, I’ll use an eyepiece in this little telescope before attaching the camera. It’s a 32mm eyepiece – that offers a 52-degree wide field of view. This is beneficial for the next step of my process.

Step 8: Star Alignment

With the mount leveled, polar aligned, and the telescope balanced. We can actually turn this sucker on. With this mount, I need to first set the “zero position“, with both axes in the home position.

After that, I’ll begin a simple star alignment routine that calibrates the mount to have precise pointing accuracy.

This means that when I punch in the deep sky object I want to image, I can be sure that the telescope will land on it and put it dead center in the frame.

Certain objects are extremely dim, so it would be impossible to know if I have the telescope pointed at it without taking a series of test exposures. This can take precious time away from imaging on a clear night – so take the time to properly star align your mount first.

star alignment routine

I personally don’t mind this stage of the process, because I honestly enjoy a little time actually looking through the telescope and getting some minor physical activity.

But I understand that there are those of you out there that are either tired of this process or have mobility issues. For these folks, I suggest using a plate solving software aid such as Astro Tortilla.

The manual process of star alignment involves slewing to 2 or 3 bright stars and centering them in first the guide scope, and then through the primary imaging telescope. Since I’ll be pointing at some of the brightest stars in the sky, I like to perform my focus routine at the same time.

Step 9: Focus and Camera Control

I like to use the live-view image from the camera during star alignment to help center the stars. Rather than centering the star in an eyepiece, I’ll jump into my camera capture software to make this process easier and more precise.

The software is called Astro Photography Tool (APT for short).

Astro Photography Tool

The Astro Photography Tool Camera Control Software Interface

A camera control software like this not only lets you automate the length of each image and number of shots to take, but they also include features to help with focus, framing, and much more.

A dedicated astronomy camera like the one I’ll use tonight does not include a display screen with an image the was a DSLR does. This means that running an additional software tool to run the camera is necessary.

To focus, I use a tool called a Bahtinov mask that creates a star diffraction spike pattern on stars that are close to being focused. During my 3-star alignment routine, I roughly center the star in the wide field guide scope visually, and then use the live-view loop with the Bahtinov mask to both center the star in the primary imaging scope, and set my focus.

how to focus

What you’re aiming for is a centralized spike between the X. Next, I’ll talk about the camera itself.

Once you’ve found the best focus possible using the Bahtinov star diffraction spike method, you can lock the telescope focuser in place using the thumbscrew in the underside of the tube. Don’t forget to take the Bahtinov mask off before capturing your light frames! (I’ve made this humbling mistake before)

To retain focus throughout the night, you may need to re-focus later on, especially if the temperature has dropped significantly. A motorized focuser such as the Pegasus Astro model I demoed over the winter makes this task much easier by allowing you to make micro-step adjustments via software on your computer.

Related Post: Focusing Tips for Astrophotography

Step 10: Setting an Imaging Sequence

With the star alignment and focus routine out of the way, we can now slew to our deep-sky target for the night.

Certain targets are better choices than others depending on your imaging conditions, moon phase, camera sensor size, telescope, filters etc. Over time, you’ll learn what your particular gear is best at, and set your self up for success whenever possible.

The camera I am using tonight is known as a one-shot-color camera. It shoots images in broadband true color, using a sensor that collects light in RGB simultaneously. A monochrome camera is capable of collecting more signal (light) at once, but a filter wheel is needed to conveniently capture each color channel needed to produce a full-color image.

This camera is called the ZWO ASI294MC-Pro. It includes a cooling feature that keeps the internal sensor cold during long exposures. This is important because a hot sensor means more noise. Noise is the little pixels and artifacts that can really make a mess of your image. With a cool sensor, you’ll be able to create images with a much better signal-to-noise ratio.

astronomy camera

The ZWO ASI294MC-Pro One-Shot-Color Camera

For those shooting with a DSLR camera:

If you’re shooting deep sky astrophotography with a DSLR, the process is slightly different than the way I have featured in the video. This is particularly evident when it comes to the focus, framing and imaging sequence setup.

With the DSLR attached to the telescope via a t-ring and adapter and/or field flattener (these adapters are usually 0.8X and both reduce the focal ratio of the telescope, and “flatten” the field of view), you’ll want to frame up your target just as you would with a dedicated astronomy camera.

The camera and telescope will need to be in focus before attempting to frame your target, and you have a few options here. One option is to focus on a star using live view on the camera itself before connecting to APT. A high ISO (1600+) is recommended while focusing and framing as it will produce the brightest stars for reference purposes.

You could also use the “live view” mode in APT. A short exposure of 4-5 seconds should be long enough to focus using a Bahtinov mask. Then, you can use a longer exposure loop to frame your deep-sky object.

Set the exposure length to about 5-10 seconds, using an ISO of 1600 or more. (6400 works well for this step). This should pull in enough stars to orientate your subject, even with a strong filter in front of the sensor. (Such as a clip-in Ha filter)

Step 11: Recommended Filters

From my city backyard, filters are necessary to capture any sort of usable image. If I want to shoot a true-color image with this camera, a light pollution filter will help ignore many of the wavelengths of light associated with things like streetlights and porch lights. My backyard is located in the center of town, rated a class 8 on the Bortle Scale.

Even then, extensive image processing must be done to separate the deep sky object from the bright sky. It’s the price we pay for being able to enjoy this incredible hobby from the comfort of our backyards.

Tonight, I’ll be shooting with a much stronger filter. It will ignore all wavelengths of visible light except for 2 very narrow bandpasses.

The STC Astro duo narrowband filter collects the light associated with Hydrogen-alpha and Oxygen only. For certain emission nebulae, it can produce jaw-dropping images in even the heaviest of urban light pollution.

The Eagle Nebula

The Eagle Nebula using the STC Astro Duo-Narrowband Filter

Step 12: Slewing to Target

With everything balanced, aligned and ready to go, we can now hop into the camera control software to set up an imaging sequence.

The target I have chosen to shoot is the Butterfly Nebula in Cygnus. It rises above my house by 10 pm and I ‘ll track it along the sky until morning. I’ll need to perform a meridian flip when the mount reaches the Zenith, which just means the telescope needs to switch sides and start tracking again.

deep sky target

For narrowband images like the one I’ll share in this post, you’ll want to use a longer exposure than you would when shooting in color.

I’ll tell the software to shoot 40 x 6-minute images. To make sure that each one of these 6-minute subs is sharp, I’ll turn on the autoguiding system.

Step 13: Autoguiding

For autoguiding, I use free software called PHD2 guiding. This tool runs my little guide camera, the Altair Astro GPCAM2. It houses a small mono sensor with one job – to follow a single star all night.

The software will communicate with the mount to make the small adjustments needed for improved tracking accuracy. I can also leverage a feature called dithering, which reduces overall noise in your stacked image by slightly shifting the position between each frame before capturing.

A way to know if your guiding is “good” or not is to view the graph tool in PHD2 guiding. A smooth graph will have a total RMS error under 1 second, as seen in the screenshot below.

PHD2 Guiding Graph

Helpful resource: Analyzing PHD2 Guide Logs

Step 14: Capture Your Deep Sky Target

Here are the individual steps I take to set up a complete imaging sequence in APT with PHD2 guiding.

  1. Connect camera (ASI driver)
  2. Choose “unity gain” setting
  3. Connect mount (iOptron Commander)
  4. Use live-view with Bahtinov mask
  5. Center 3-star alignment stars
  6. Focus on alignment star using star diffraction spike pattern
  7. Remove Bahtinov mask
  8. Slew to target
  9. Set cooling to -20 (Cooling-Aid)
  10. Slew to target
  11. Adjust target framing using 20-30 second live view loop
  12. Run and calibrate PHD2 guiding
  13. PHD2 guiding with smooth graph
  14. Ensure dithering is active
  15. Start imaging plan (eg. 30 x 300-second subs, Binned 2×2)
  16. Grab a beer and watch each image appear!

Here is the image I captured using this setup on the night I recorded the video. The image includes just over 6 hours worth of total integrated exposure time using 6-minute images.

After collecting all of my light frames for the image, I took 20 dark frames that I’ll use during the stacking process. Dark frame subtraction is the process of defining the digital noise created by the camera sensor, and removing it from your final image.

The images were stacked in DeepSkyStacker to improve the signal-to-noise ratio before being processed in Adobe Photoshop to pull out more color and detail.

IC 1318 - The Butterfly Nebula

The Butterfly Nebula is located in the Sadr Region of Cygnus, and it an excellent astrophotography target to capture in narrowband hydrogen-alpha.

Final Thoughts

If you’re brand new to astrophotography, I hope you now have a better understanding of the process involved in capturing deep sky objects through a telescope. It may seem like a lot to take in all at once – because it is!

The good news is, if you are dedicated and passionate about astrophotography, small victories and improvements along the way are all you will need to keep going.

I certainly didn’t get to where I am at today in a hurry. Why would I rush through something I absolutely love doing?

My final advice to you would be to be patient and remember to enjoy each small victory along the way. The night sky is not going anywhere, and you have the rest of your life to explore it.

astrophotography step-by-step guide

Related Tags

Selective Processing for More Detail

Staying Inside – Image Processing

The unseasonably cold weather and precipitation we have experienced here in Southern Ontario have given me the perfect opportunity to go through my old astrophotography images and reprocess the data.  I have been advancing my image-processing skills by studying current astronomy images taken by the pros.

Being a creative professional myself, I have always understood and appreciated the power of inspiration. I am always interested in new image-processing techniques, Photoshop tutorials and new software that can enhance my work.  Through selective processing, I have been able to squeeze out the most amount of detail from my astro images.

Western Veil Nebula

The Western Veil Nebula – I reduced the stars to show more contrast in the nebula

My latest take on The Swan Nebula is my favorite version yet. Through selective processing, I was able to tame the background stars, while intensifying the gorgeous pinks and reds in the nebula itself.  

I also recently reprocessed my wide-field image of the Western Veil Nebula, with a focus on reducing star size, and overall image contrast and color. The “witch’s broom nebula” is a tough process, especially if you have to deal with a severe gradient behind all of those stars. After assessing the gradient in Photoshop, (mostly due to heavy light-pollution) I can easily even out the sky background using the Gradient Xterminator plugin.

I am quite pleased at my latest results of the Eagle Nebula as well. I went through my astrophotography folders from the past 4 years (like I said, it’s been cloudy!)  and found a set of almost 2 hours of frames on M16 that I had not previously used!  

I combined all of the data together from May 2012, and May 2013 in DeepSkyStacker to create an image with over 3 hours of exposure time.  I decided to keep the extremely wide-field view captured by my 80mm telescope, rather than cropping the photo around the nebula.

This image really benefited from the selective processing technique. By reducing the stars on a separate layer, I was able to keep all of the detail found in the nebula.

Eagle Nebula - 80mm Telescope

Wide field image of the Eagle Nebula with my 80mm telescope

Image Processing Techniques

One of the processing techniques I have been implementing into my photos is to process different elements of the image separately. By this, I mean to process the background, the stars and the nebulosity on their own.  

I am able to do this by selecting each element of the image and stretching the data without affecting the other areas. For example, I can boost the vibrance and saturation of the nebula or galaxy without adding additional noise to the background of space and stars.

As I have stated many times, I prefer to tame the stars in the image to be as small as possible. Normally, I would run the “make stars smaller” action to the entire image in Photoshop.

This actually starts to diminish the precious detail in your deep-sky object that you worked so hard to capture! Many other actions that are intended to correct issues with the background space and stars can take away from your subject as well.

You can also manually Remove the Stars Completely from your image using photoshop.

Swan Nebula - 8 Inch telescope

My latest version of the Swan Nebula

Selective Processing

There are several ways to accomplish the selective processing technique to your astronomy photos.  You can create multiple adjustment layers of your image in Photoshop, and apply the various actions to each element of the image on a separate layer.

I use the Select and Mask tool to refine my selections before applying effects. This ensures that each new adjustment layer is blended naturally into the final image.

 Once you have applied your desired settings applied to each layer, you can use layer masks to combine all aspects of the photograph into one.  This means you will likely have layers for:

  • The Background Space – With a balanced black-point set

  • The Background Stars – Small, sharp and with lots of accurate colour

  • The Brighter Stars – Soft, or with Diffraction Spikes and Color

  • The Deep-Sky Object – Full of luminance, color and detail

  • The Core or Brightest Area of the DSO – reduced to show detail, not blown out

Selective Processing - Astrophotography

Processing the nebulosity separately from the background stars in Photoshop

You can also process the selected elements of your images as separate documents.  Sometime I prefer to do this to really focus on achieving the best possible result for my focus area, without the temptation to poke around at another feature.  

Once you have processed each version of the image with your focus area maximized, you can then combine the images using layer masks.  The blending and layer masking is definitely the most delicate stage of the process.  You can really make a mess of an image by failing to inspect all areas of your image before flattening.

I find it helpful to use a reference image of your deep-sky target. This is the best way to make sure you have not overstretched your image data, and that your colors and details are an accurate portrayal of that particular deep sky wonder. I often look for inspiration on APOD!  

To stay connected with me and my latest astrophotography images, please follow my Facebook Page.  I hope you are all excited about the wonderful deep-sky targets that will be gracing our night sky the coming months, I sure am!

Resources:

Astrophotography for Beginners – The Basics

How to choose an Astrophotography Camera – My Advice

Top 5 Telescopes for Beginners – My Advice

Related Tags