Skip to Content

deep sky astrophotography

Deep Sky Astrophotography in Light Pollution

|Nebulae|5 Comments

If you’ve been following AstroBackyard on YouTube, you’ll know that I regularly shoot DSLR astrophotography images under the heavily light polluted skies at home. My night sky is classified as Bortle Class 8 in terms of sky quality, a white zone on the light pollution map. This certainly makes things more difficult in terms of collecting data and image processing, but I welcome the challenge.

It’s true, there is no substitute for dark skies. But being able to set up a portable astrophotography kit in the backyard on a weeknight is pretty cool. I don’t have to pack up heavy gear into the car and worry about mobile battery power or internet access. I can open up the garage door and start capturing images through my telescope before it gets dark after work.

light pollution map

I live in the center of town, a red zone on the light pollution map

Don’t get me wrong, I adore traveling to dark sky locations, it just doesn’t happen as often as I’d like it to. For me, a typical night of deep sky imaging happens during the week in between work, family time and lots of dog walking. A clear sky in the backyard is my idea of the perfect night, no matter which target I’m shooting.

I’ve been successfully capturing deep sky images from this light polluted backyard for 3 years now. The best part about it is that I get to show others that live in the city that deep sky astrophotography is not only possible, but you can capture some truly incredible images. In this post, I’ll share my latest results from the backyard using a Canon EOS Rebel T3i DSLR camera and a small refractor telescope.

deep sky astrophotography

The Soul Nebula captured with a Canon DSLR and the equipment shown below

Light pollution is a major side-effect  of urbanization, and is said to compromise your health and can disrupt ecosystems. To discover the amount of light pollution where you live, simply locate your house on this interactive light pollution map. The Bortle scale is a way of measuring the brightness of the night sky.

Photographing a Nebula from the City

After much deliberation, I have decided to dedicate an increasingly rare and precious clear night to the Soul Nebula in Cassiopeia. I’ve photographed IC 1848 before, so I’ll be combining the new images I take with the previous data to create my best image of this emission nebula yet. All of the data I’ve ever collected on this nebula was shot here in the backyard with a DSLR.

My secret weapon is to collect absolutely as much exposure time on my target as possible. Stacking several images together can increase the amount of signal collected while reducing noise by canceling out its random output. For more information about the concept of signal-to-noise ratio, Craig Stark explains it better than I ever could.

astrophotography telescope

My telescope with the Canon EOS Rebel T3i attached

Overcoming light polluted skies

I’ve got lots of experience here, as the majority of my deep sky astrophotography is done from home. In theory, a light pollution filter will let you shoot longer exposure times before being blown out on the histogram, but this comes at a price. The signal (light) is often weak, and the natural color emitted from the stars has been altered. For both of these trade-offs, capturing more integrated exposure time can be a huge help.

A popular and effective method of overcoming the light polluted skies of an urban backyard is to use a monochrome camera equipped with narrowband filters. This has the power to aggressively ignore artificial light and isolate the light associated with specific gases in objects in space. But what about those shooting with a DSLR camera?

A color camera like a DSLR uses an internal Bayer matrix to create full-color images in a single shot. This convenience comes at the expense of a much weaker signal when compared to a monochrome CCD or CMOS camera. To offset this challenge, I like to use camera filters that help me isolate the light I want to collect.

camera filter

I use a clip-in light pollution with my Canon DSLR (Skytech CLS-CCD)

Shoot During New Moon

Although narrowband filters have allowed me to take photos during all moon phases, the new moon phase is a special time for amateur astrophotographers. The days surrounding the new moon phase mean that I can finally capture true color images of my subject with more natural colors.

Believe it or not, the bright glow of Earth’s natural satellite produces enough skyglow to really reduce contrast in your deep sky images. Even a narrowband filter won’t help if your target is sitting too close to a bright full moon.

Light pollution filters such as the Astronomik CLS and IDAS LPS D-1 help to reduce moonglow, but for the absolute best data on a deep sky target, the new moon phase is best. If you’re planning on shooting unfiltered, this is definitely when you want to try it.

Shooting Without a Light Pollution Filter

It’s also worth noting, that for certain targets, an incredible image can be captured without using a filter at all. Don’t believe me? Have a look at this photo of the Andromeda Galaxy posted by Jon Rista on Astrobin. The image was created by stacking 174 x 150-second subs at a modest ISO 400 under light polluted skies. Inspired? I was too.

I plan to capture the Pleiades from my backyard again soon using only the required UV/IR (luminance) filter with my modified DSLR. This target does not emit light that a narrowband filter can isolate, as it is a reflection nebula. Another target that would be a great test subject for this technique is M31, as seen in Jon’s image above.

Update:

I captured the Pleiades star cluster using a new light pollution filter, the Optolong L-Pro. This is a multi-bandpass filter the does a great job of preserving the natural star colors in my images from the city. Have a look at sample image comparing an unfiltered image and one using the Optolong L-Pro:

filter comparison

My full review of this broadband astrophotography filter includes an image of the Pleiades star cluster captured with a stock Canon 5D Mk II camera.

Optolong L-Pro Filter Review – An Urban Broadband Astrophotography Filter

Selecting a Target

I no longer go into my astrophotography projects blind. In the early days, I would set up my telescope and astrophotography gear and think to myself “what will I shoot tonight?”. As carefree and exciting as those nights were, they also included a lot of wasted clear sky time looking at a computer screen while the night passed me by.

These days, I prefer to take a much more organized approach to deep sky astrophotography as my time is limited, and clear nights are rare. I find it best to double down on deep sky targets that not only compliment my equipment but maximize exposure time and increase the chances of “completing” a final image.

astrophotography book

I often refer to my “The 100 Best Astrophotography Targets” book for inspiration (On Amazon)

My decision-making process involves answering the following questions:

  • Have I photographed this target before?
  • Is the target in the early, mid or late position for the season?
  • Is it a good fit for the focal length of my telescope?
  • Does this object require narrowband data to properly showcase?
  • Will it turn out well in color using a DSLR camera?

As an example of a target’s position relating to the season – you wouldn’t want to start a new astrophotography project on a DSO that is on its way out and fading deeper and deeper into the Western twilight each night. Right now, Orion (winter target) is in the early season stages, while objects like the Crescent Nebula (Summer target) are on their way out.

It’s beneficial to select a deep sky target that will get as high from the horizon as possible. This will, of course, vary by your location but aim to collect light on subjects that are in their optimal position for the time of year. Your backyard window of the sky and potential obstructions in your yard will also factor into your selection.

deep sky imaging setup

My deep sky imaging setup in the backyard

Despite having several previous iterations of IC 1848 on my hard drive, The Soul Nebula checked off the most boxes and won the battle for option selection. It currently sits in an opportunistic area of the night sky to collect a serious amount of exposure time this month.

This will be a great opportunity to improve my broadband color data collected on the Soul Nebula to improve upon my image from last year.

Why I’m using a DSLR

With a number of dedicated astronomy cameras and cooled CMOS cameras in my possession, why would I opt for using an old DSLR camera instead of impressive astronomy camera like the QHY128C? (I’m working on it)

For starters, I wanted to produce another example image using the Zenithstar 73 APO with a DSLR. In my last video I shared images of the heart Nebula and Butterfly Nebula in narrowband Ha – but this time I’ll collect images in good old full color. My results on the Soul Nebula should give you a good idea of what to expect with a crop sensor DSLR camera like my Canon T3i or similar models.

A telescope like the Zenithstar 73 is a logical telescope choice for deep sky beginners just entering the hobby, and many of those people will be using a DSLR. It’s easy to get carried away in my posts and videos and skip over the basic information beginners are looking for, so I’ll try my best to scale back when the situation calls for it.

connecting a DSLR to a telescope

My DSLR attached to the Flat 73 Field Flattener and Zenithstar 73 Telescope

Camera Settings for a Washed Out Sky

From my bright sky here in the city, I’ll use 3-minute exposures at ISO 800 to capture the Soul Nebula. This is a rather conservative approach, which may have you wondering why I’m not shooting longer subs. A typical DSLR light frame under moderately light polluted skies would normally be 5 minutes at ISO 1600, but it’s a hot a humid night, and those settings would absolutely cook my sensor.

In these conditions, there is little value in collecting images longer than 3-minutes. As the noise increases significantly, the signal sees very little improvement. You are much better off capturing several shorter images over time. (My camera sensor hit 32°!) Even at 180-seconds, I am capturing A LOT of skyglow that will have to be dealt with in post-processing.

Camera Settings in the City

  • Mode: Manual
  • Format: RAW
  • ISO: 800
  • White Balance: Auto
  • Exposure: 180-seconds (3 minutes)

*Note without using a light pollution filter, this exposure time would be cut in half.

light frames

Previewing my 3-minute light frames in Adobe Bridge before stacking

Focal Ratio is Important

The Zenithstar 73 APO is fast. It’s fixed f-ratio of F/5.9 can collect light faster than most of the refractor telescopes I’ve used in the past (Including my Explore Scientific 102). This gives my images a much-needed boost in signal for each short 180-second sub. A lower focal ratio allows more photons to hit your camera sensor in a single exposure, which makes a big difference in terms on SNR.

Naturally, the aggressiveness of the filter (in this case a SkyTech CLS CCD) in front of the camera sensor changes how much signal I can record in a single exposure.

White Balance

I’ll leave the cameras white balance set to auto, as I see no benefits in adjusting this setting at this stage. Because I am shooting the images in RAW format, I can manually adjust the white balance to whichever temperature I want in post-processing. With that being said, there have been some interesting discussions on the topic of the benefits of using a custom white-balance for astrophotography in heavy light pollution.

Capture Software

The images are being captured using APT (Astro Photography Tool) on my new laptop computer. Autoguiding through PHD2 guiding and the Altair GPCAM + 50mm guide scope mean that each image contains sharp stars each and every time. If you’re looking for an affordable autoguiding package to upgrade your kit, have a look at the Starfield autoguiding package offered from Ontario Telescope.

The images are dithered between each frame to further reduce noise – which can easily be switched on within the gear tab of APT. To learn more about the process of data acquisition including the use of support files (dark frames, flat frames), please visit the get started page.

Light Pollution Filter for Canon DSLR’s

For broadband spectrum targets like galaxies (and many reflection nebulae), a light pollution filter is less effective. However, for an emission nebula like the Soul Nebula, isolating the light emitted in the H-Alpha and OIII wavelengths can make a big difference.

Longtime followers of the blog will remember the SkyTech CLS-CCD filter I reviewed last year. Time and time again, this filter has impressed me with its ability to produce impressive color images using my DSLR camera in heavy light pollution.

Light pollution filter for Canon

The SkyTech CLS-CCD clip-in light pollution filter for modified DSLR cameras

This filter has been my go-to choice when it comes to capturing true-color broadband images from home. It does a great job of creating contrast between my target and a washed out city sky. The only downside is that it also alters the color balance of my image and paints the surrounding stars with a red cast.

Later this month, I’ll be testing out an Optolong L-Pro filter with my DSLR camera, which is said to be “a true 5 bandpass filter”. This multi-bandpass filter is less aggressive than the CLS-CCD and should help with my color balance issues. My hope is that this filter is a much needed middle ground between shooting with the CLS-CCD filter and unfiltered. I expect my exposures to be shorter using this filter here in the city.

Optolong L Pro FIlter

The Optolong L Pro Filter is 5 Bandpass Light Pollution Suppression Filter

For Stock Canon DSLR cameras

Owners of stock (non-modified) DSLRs will want to get a standard CLS (city light suppression) filter such as the Astronomik CLS clip-in filter without the unnecessary UV/IR cut filter. If you’re unfamiliar with what it means to modify a DSLR for astrophotography, have a look at this page where I cover this aspect of astrophotography cameras and more.

The Soul Nebula in Cassiopeia

With an apparent size of 150′ × 75′, the Soul Nebula is a fantastic deep sky astrophotography target for a DSLR camera and compact wide field refractor telescope. It also rises above the roof of my house just as nightfall sets in, which is perfect timing in terms of maximizing my imaging time.

It’s a beautiful emission nebula with several embedded open star clusters. It emits a strong amount of light in the hydrogen-alpha wavelength, which makes adding images captured through an Ha filter beneficial.

star map of the Soul Nebula

Where to find the Soul Nebula

If you’ve been following my backyard activity via the email newsletter, you’ll know that I’ve been using another exquisite compact refractor. This time, it’s the William Optics Zenithstar 73 APO, and my resulting image should give you a good idea of what you can expect from this affordable doublet from an urban sky.

My Telescope

The William Optics Zenithstar 73 APO is a compact F/5.9 doublet apochromatic refractor with an impressive entourage of accessories to get you up and running. The Flat 73 1:1 field flattener is an essential upgrade if you plan on imaging with a full frame camera.

This telescope has a focal length of 430mm, which creates an extremely wide field of view. This means that it is well suited for large nebula targets like the Soul Nebula or Heart Nebula in Cassiopeia, but less effective on smaller targets such as galaxies.

The package I have includes a guide scope rings and a matching 50mm guide scope with gold accents. Using the M48 Canon adapter, I thread my Canon T3i to the Flat 73 for incredible wide field exposures of my target of choice. Owners of DSLR cameras looking for an easy entry point into deep sky astrophotography should look no further than the Zenithstar 73 APO.

DSLR camera and telescope

The William Optics Zenithstar 73 APO is available at Ontario Telescope

It’s incredibly compact and manageable to use. If you’ve ever fought with balancing a large reflector telescope on a mount, you’ll really appreciate a compact telescope like the Z73. There is less stress on the mount, meaning can effortlessly track your target, even if the overall payload balance isn’t perfect.

One of my favorite features is a simple yet ingenious design touch. They’ve built a Bahtinov focus mask into the lens cap.

Focusing the image with the Z73

The diffraction spikes focus mask is a convenient feature you’ll find in all new William Optics refractors. To focus with my DSLR, I simply find a bright star in the live view screen with the focus mask attached. Because the material is made from optical acrylic rather than metal, this mask provides 92% light transmission.

DSLR camera sensors are not as sensitive as most dedicated astronomy cameras. So the added light transmission from this mask really comes in handy when focusing your star using the rather dim 10X live view mode.  You’re presented with nice long diffraction spikes to really nail down your optimal focus position.

focus bahtinov mask

The built-in Star Diffraction Spikes Bahtinov Mask on the Z73

You’ll need a telescope mount that’s capable of handling a refractor telescope, but its small size means that beginner level astrophotography mounts such as the Orion Sirius EQ-G, Celestron AVX or Sky-Watcher HEQ5 will perform well with it.

My Telescope Mount

The Sky-Watcher HEQ5 SynScan pro has been called in for duty to capture sub guided 3-minute subs on the soul. It’s more than capable of accurately tracking this gorgeous nebula with the 5.5-lb Zenithstar 73 APO attached. I purchased this mount from a Canadian astronomy classified website several years ago, and it’s been working flawlessly ever since.

It allows me to set up quickly and easily Polar Align the mount within minutes. I still use the SynScan hand controller to star align the mount and slew to my target, although most prefer to advance to using the EQMOD software to control this mount from their PC.

tracking telescope mount

My Sky-Watcher HEQ5 SynScan Pro Telescope Mount

Speaking of Sky-Watcher, I am not done with the Esprit 100 ED just yet, not even close. With the departure of the iOptron CEM60 mount a few weeks ago, I had to find a solution to carry my heavier telescopes.

I am excited to announce the arrival of a brand new Sky-Watcher EQ6-R GoTo Mount as of this week. The built-in illuminated finder scope, SynScan hand controller and snow-white finish will all feel very familiar – except there’s no rust on the counterweight!

I’ll have much more information to share about this soon.

Conclusion and Results

Mother nature doesn’t care what the calendar says, because Tuesday night’s imaging session was a nearly record-setting 31 degrees in Southern Ontario. Unfortunately, this increased the amount of noise in my images of the Soul Nebula (Sensor at 32°), but luckily my total integration time helped to improve the SNR.

Shooting with an uncooled DSLR is not ideal on hot nights like this – but nights like this are numbered, and soon I’ll be complaining about numb fingers, not camera noise.

The following image combines my latest data with images of the same target collected last year. All of the images were captured using a modified Canon EOS Rebel T3i camera and SkyTech CLS-CCD filter from the backyard.  The only difference in acquisition details between 2017 and 2018 was the use of a Meade 70mm Quadruplet Astrograph in 2017.

Narrowband Hydrogen-alpha data was added as a luminance layer to this image using the HaRGB method in Adobe Photoshop. This is a powerful way to boost signal in an emission nebula captured under heavily light polluted skies. For these images, an Astronomik 12nm ha clip-in ha filter was placed inside of the camera.

The Soul Nebula

IC 1348 – The Soul Nebula captured from Bortle Class 8 Skies with a DSLR Camera

The images captured this week on the Soul Nebula using the Z73 totaled 3 hours and 15 minutes (65 frames). As expected, the final still contained a fair amount of noise, even with the aid of dark frames and over 3 hours of exposure time. Doubling my integration time would certainly help.

The images were registered and stacked in DeepSkyStacker, with the final image processing done in Adobe Photoshop. The Astronomy Tools Action set contains many useful one-click actions that I regularly use on images like this taken from the backyard. (You can find a list of the software I use to process my images on the resources page)

Darker skies have a clear advantage when it comes to capturing deep sky astrophotography images. But with enough exposure time and the right image processing strategy, you can capture breathtaking images from your own backyard – no matter how light-polluted it may be.

Equipment Mentioned in this Post

Sky-Watcher HEQ SynScan Pro GoTo Mount (Now the AZ-EQ5)

William Optics Zenithstar 73 Refractor Telescope

William Optics Flat 73 Field Flattener

Canon EOS Rebel T3i (full spectrum modification)

SkyTech CLS-CCD Clip-in filter for Canon EOS

Astronomik 12nm Ha Clip-in filter for Canon EOS

AmazonBasics USB 2.0 A-Male to Mini-B (6 feet)

Replacement AC Adapter (Battery Replacement) for Canon T3i

 

Related Tags

Deep Sky Astrophotography Step-by-Step Walkthrough

|Tutorials|10 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.

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 axis, 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

An 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 because 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 current time.

Then, it’s just a matter of matching up what the app tells me on the mount be 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 cant see polaris. You should probably check out the Polemaster.

polemaster

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 axis, 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 tonight 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 in to 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 axis 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.

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 you 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 using 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 too 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.

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 a 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. 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