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Ha filter

Astrophotography with a 12nm ha filter

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With the aid of an Astronomik 12nm Ha filter, I can capture deep-sky images more often than ever before. With both the Canon EOS clip-in version for my DSLR and the 2″ CCD round mounted version for the my dedicated astronomy camera, I collect photons in every moon phase.

Despite the bright 80% illuminated moon this past Saturday night, I was able to capture some incredible deep sky photos of 2 deep sky emission nebula targets from my backyard in the city. Using my 102mm refractor telescopes, I collected isolated wavelengths of light on the Wizard Nebula in the constellation Cepheus, and Bubble Nebula in neighbouring Cassiopeia.

A narrowband Hydrogen-alpha filter (Ha) has the power to cancel out nearly all of the surrounding city glow and moonlight in the sky. In seemingly magical fashion, it reveals the faint nebulae in the night sky that are impossible to see through an eyepiece with the naked eye.

In the photo below, you’ll see my Explore Scientific ED102 refractor telescope, with an imaging payload that includes a 48mm (2-inch) Astronomik round mounted 12nm Ha filter. This filter is threaded to the nosepiece of my field flattener/reducer and fits securely into the focuser of the telescope.

Deep sky astrophotography telescope

In this post, I’ll discuss the advantages that a 12nm Ha filter can provide to your deep sky imaging experience. Whether you use a dedicated astronomy camera (mono or color), or a modified DSLR, a narrowband h-alpha filter will likely be the most useful filter you’ll ever use for astrophotography.

I personally had no idea what I was missing out on before I dove head first into narrowband astrophotography with my DSLR. You’ll need an astro-modified DSLR or dedicated astronomy camera to see the true benefits of this technique, which I will discuss in detail shortly.

Astrophotography with a 12nm ha filter

My current one-shot color CMOS camera performs exceptionally well with narrowband filters. Sure, a camera with a monochrome CMOS or CCD sensor with TEC (cooling) would outperform it, but I have a strange love of pushing my current gear to its limits.

The Altair Hypercam 183C includes internal fan cooling which keeps the sensor much cooler than a traditional DSLR. This comes in handy when shooting with a narrowband Ha filter, as you generally will want to shoot even longer exposures than you would in color. (This depends on your camera and the settings used)

After a very warm start to fall, the reality of a Canadian October night set in as the temperature plummeted to 4 degrees Celcius on Saturday. Who needs internal cooling when it’s freezing outside? It really is a great time of year for DSLR astrophotography – as the sensor can return to a more suitable temperature for long exposure imaging.

In the video below, you’ll get a behind the scenes look at my process of capturing the Bubble Nebula using an Astronomik 12nm Ha filter.

For an idea of what to expect when using a color camera, have a look at the following image of the Wizard Nebula captured in the Hydrogen Alpha wavelength. The individual image frames were captured using a gain setting of 60% on the 183C astronomy camera with a 12nm Ha Filter in front of the sensor.

The photo includes over 5 hours worth of 210-second exposures:

Wizard Nebula using a 12nm Ha Filter

The Wizard Nebula in Ha – Altair Hypercam 183C Color CMOS Camera

Total Exposure: 4 Hours, 54 Minutes (84 frames)

The reason the photo is black and white is that it was created by extracting the red channel from the original data collected from the color CMOS sensor. This process is easy to complete using Adobe Photoshop, by copying the data from the red channel to a new image.

You can then process the Ha data separately, as you would with luminance data from a monochrome camera. Again, the signal is not nearly as impressive as it would be using a dedicated monochrome camera, but it can certainly improve your existing color images.

To illustrate this point, I have added the additional light in captured Ha to existing some existing RGB (color) data on the Wizard Nebula. The HaRGB composition method continues to produce incredible results from my light polluted backyard.

Wizard Nebula in HaRGB

Using an H-Alpha Filter with a DSLR Camera

A DSLR camera is a fantastic way to start enjoying narrowband astrophotography with an H-Alpha filter, but there’s a catch. You must be willing to modify your existing stock DSLR camera (I modded my Canon 450 using this video as a reference) or purchase a pre-modified camera from a vendor that specializes in this service.

One point of confusion amateur DSLR astrophotographers may face is the description of the filter, and whether or not it is a good fit for your camera. For example, the Astronomik website lists the filter as a “narrow band filter for CCD photography”. So will this filter be effective with the color CMOS sensor in your DSLR?

DSLR Ha filter

The 12nm Astronomik Ha Filter – Clip-in version for Canon EOS DSLR’s

The answer is yes, but you’ll need to have a modified camera to reap the full benefits of a Ha filter. By modified, I mean that the internal stock IR cut filter has been removed from the camera sensor. There are professional astrophotography camera modification services available to perform this upgrade if you are not up to the task yourself.

The stock IR (Infrared) filter inside regular DSLR cameras is there to produce natural looking photos for daytime photography, yet blocks out certain wavelengths of hydrogen-alpha light emitted by emission nebulae in the night sky.

For my Canon Rebel T3i, no additional IR cut filter replaced the stock one that was removed, and this is called a “full spectrum modification”, or “naked sensor mod”. Because I have not installed a replacement UV/IR filter inside the camera, I need to make sure that I always use an external UV/IR filter to properly focus my broadband (color) images.

An example is the SkyTech CLS-CCD filter that I use to collect color images from my light polluted backyard. The “CCD” portion of the name is referencing the added bandpass filters a modfied DSLR camera requires to focus.

A 12nm Ha narrowband filter can dramatically increase the contrast between your deep sky object and a bright city sky. It suppresses the emission lines of artificial lighting such as Mercury and Sodium, leaving only the intense details of the h-alpha light wavelength in your image.

Using a DSLR camera with an h-alpha filter means that all of the “good” signal (not noise) will reside in the red channel. To showcase this trait, have a look at the comparison of blue signal vs. red in this narrowband image of the Heart Nebula.

channels in Photoshop

In September 2018, I captured images of two emission nebulae using my modified DSLR camera and a 12nm Astronomik Ha filter. The camera was attached to a wide field refractor telescope, the William Optics Zenithstar 73 APO.

If you currently shoot color deep sky images with a DSLR camera, I urge you to consider the idea of modifying it for astrophotography. You can then begin to tap into the amazing benefits of narrowband imaging using an h-alpha filter such as the Astronomik 12nm clip-in version.

The fact that you’ll be able to capture powerful images during a full-moon alone is worth the effort. Some of my most memorable astrophotography projects are HaRGB composite images that combine broadband RGB color images with added luminance signal of hydrogen-alpha.

A great feature of the clip-in variation of the Astronomik Ha filter is the ability to use it when a camera lens is connected. This means that you can capture wide field images of the night sky that isolate the interesting regions of emission nebulosity. Below, is an image created using a ha filter in conjunction with a 50mm camera lens on an iOptron SkyTracker mount:

Barnard's Loop in Orion

The Orion Constellation in H-Alpha using a 50mm Camera Lens

Creating an HaRGB Composite

Then, I combined the images shot in Ha with my color version of the image – shot through an Explore Scientific UHC filter. This creates a composite version of the NGC 7380 that uses the grayscale H-Alpha image as a luminance layer.

Next up is NGC 7635 – the Bubble Nebula. This is just the beginning of a full narrowband project that will include OIII and SII. This project will likely carry on through the month of October – as I will need to wait for New Moon to capture the broadband color images.

With Saturdays imaging season, I the project is off to a great start.

The Bubble Nebula in Ha

Bubble Nebula with a 12nm Ha Filter

NGC 7635 – The Bubble Nebula in Ha

Photo Details:

  • Exposure Time: 3 Hours, 33 Minutes (61 frames)
  • Camera: Altair Hypercam 183C (Gain 60%, Bin 2 x 2)
  • Filter: Astronomik 12nm Ha Filter

At this point, I have also collected images using the Astronomik 12nm OIII filter as well.  Another cold clear night in the backyard yeilded over 4 hours worth of total exposure time on my project.  The details of the Bubble Nebula in OIII are less dramatic than the h-alpha, but a necessary stage in my narrowband project.

The Bubble Nebula in OIII

Bubble Nebula using an Astronomik 12nm OIII filter

The Bubble Nebula in OIII

Photo Details:

  • Exposure Time: 4 Hours, 43 Minutes (81 frames)
  • Camera: Altair Hypercam 183C (Gain 60%, Bin 2 x 2)
  • Filter: Astronomik 12nm OIII Filter

Final Thoughts

I hope that you have enjoyed seeing my progress into narrowband deep sky astrophotography with the use of filters. The color CMOS sensor camera I am using is not ideal for this type of photography, but it certainly gets the job done with a little patience.

Ha Filter Astrophotography

I look forward to completing my narrowband project on the Bubble Nebula this month and will be sure to share my results.

With that being said, I am happy to announce the arrival of a Mono Camera as early as late October.  This is a brand new astrophotography camera at an entry-level price point.  Until next time, clear skies!

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How a DSLR Ha Filter can Improve your Astrophotos

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Some of the most incredible DSLR deep-sky images ever produced, likely combined regular RGB data (A typical color image) with images using a Ha filter.  A clip-in filter for your camera such as the Astronomik H-Alpha 12nm CCD filter makes it easy to start gathering Hydrogen-Alpha images with your existing DSLR.

When it comes to astrophotography from a city backyard, narrowband filters such as H-Alpha allow you to collect detailed photos of many of your favorite nebulae and galaxies. The resulting greyscale images can then be applied to any existing full-color data you may have for an even more powerful image than in true-color alone.

Narrowband filters are an astrophotographers best friend.

Canon EOS Ha Filter

The Astronomik H-Alpha 12nm Clip Filter for Canon DSLR’S

This narrowband filter lets the h-alpha light of emission nebulae pass through to the camera sensor, and blocks almost all of the other light spectrum.  What does this mean?

It means that city light pollution and moonlight are completely erased!  This opens up the doors to imaging during the full moon, and from a city backyard.

No more waiting until the new moon phase for deep-sky imaging!

 

Emission Nebulas and Hydrogen-Alpha

Emission nebulas are clouds of glowing gas, and they emit light at a very specific wavelength.  This is information is beneficial to astrophotographers as we are able to isolate this wavelength for photography. The light from an emission nebula is created when the atoms in the gas are ionized by the formation of hot young stars.

The dominant wavelength in a hydrogen nebula is the deep red portion of the spectrum known as the hydrogen-alpha line (656nm to be exact).

 

visible spectrum - wavelengths in nm

The Visible Spectrum – Wavelengths in Nanometers

Why this is important for DSLR astrophotography

By using a Ha filter in your DSLR, it is possible to increase the contrast between objects in the h-alpha emission line and the skyglow background.  The filter completely suppresses the emission lines of artificial lighting such as mercury (Hg) and sodium (Na).  The particulars of the Astronomik ha filter can be understood in the graph below.

 

Ha Filter Wavelengths

Chart showing the the 97% transmission of the h-alpha wavelength

Images captured using a narrowband Ha filter have some pleasing characteristics.

At the top of the list is reduced star size.  This further emphasizes the detail and contrast of a deep-sky image by allowing it to stand out from the surrounding sea of stars.  Filtering out skyglow and light pollution means that longer exposure times of 5 minutes and beyond from the city are possible from the city.  You will likely capture more detail in your subject than ever before. 

Here is an example of what is possible with a modified Canon DSLR and a 12nm Ha filter.

Soul Nebula in Ha

The Soul Nebula in H-Alpha

Choices – 12nm or 6nm versions

The 6nm version of the Astronomik Ha filter has an extremely narrow emission-line filter.  This version targets an even narrower portion of the visible spectrum, blocking nearly the whole remainder of the spectrum.  So wouldn’t the 6nm version the obvious choice?

Despite the increase in contrast and more light-blocking power of the 6nm version, there were a few reasons I went with the 12nm.

 

Ha filer

The filter clips into your DSLR over the sensor

A major step in my pre-imaging routine includes framing my deep-sky target to include as much of the object and surrounding elements as possible.  BackyardEOS streamlines this task with the frame and focus feature.

 

6nm Ha filter for Canon DSLR

The 6nm Ha filter from Astronomik

With the 12nm Ha filter installed in my DSLR, this becomes a much more difficult process when framing targets without any significantly bright stars in the frame!  The same scenario transpires when focusing the camera.  Not only is focusing stars using live-view out of the question, but test exposures may need to be as long as 10 seconds before anything appears.

It’s not the end of the world, but it does take longer to get up and running.  The 6nm would double these impacts, and increase this setup time.

Many backyard astrophotographers would disagree, wishing they had gone with the 6nm instead.  Ideally, having both filters would provide maximum H II contrast while retaining stars in the image.

Does my camera need to be modified for astrophotography?

Absolutely not.  The same benefits of an H-alpha filter can be realized with a stock DSLR.  However, the amount of red light your camera will be able to record will be drastically reduced.  If you are serious about your astrophotography, it is worth thinking about modifying your camera either yourself or by a professional.  Here is a shot of the Eagle nebula using the Astronomik Ha filter and a stock Canon EOS 7D.

Using an H-Alpha filter with a stock DSLR

Example of a Ha filter with a stock DSLR

This is typically what a frame looks like taken using a Ha filter through a DSLR.  This emission nebula could have been captured in greater detail using a modified camera, but the skyglow and wavelength suppression capabilities of the filter are still present.

I am a huge promoter of DSLR astro-mods.  If your camera is used for astrophotography exclusively, why not modify your camera yourself?

Modified camera for astrophotography

Modifying a Canon DSLR for astrophotography

If you have either a light pollution or h-alpha filter covering your DSLR sensor at all times, you are not required to install any extra replacement filters.  I carefully removed the IR cut filter on my Canon Rebel 450D by watching this video from Gary Honis.  This is known as a full spectrum “naked sensor” mod, and it was the best decision I ever made.

Processing H-Alpha frames taken with a DSLR

What about image processing, is it different than a regular RGB image?  Yes, there are some differences in the stacking and processing procedures, but not many.  It is still important to take as many exposures (light frames) as possible, to increase your signal-to-noise ratio.  Capturing dark frames will also have the same noise-reducing qualities when stacking images using an H-Alpha filter.

This video tutorial should help you understand the process:


 

In a nutshell, the Hydrogen Alpha version of your astrophoto will use the Red channel as a luminance layer that you will then merge with your RGB version.

 

HaRGB in Photoshop – Adding Ha Data to an RGB Image

Hydrogen-alpha images are essentially black and white images.  By combining them will a full-color RGB astrophoto it is possible to create a beautiful composite photo.  Adobe Photoshop is more than capable of accomplishing this task.  I’ll cover this processing method in an upcoming step-by-step tutorial.

Below you will find a simple example of what Ha-RGB processing in Photoshop can accomplish.  For the example below – a very limited amount of interated exposure time was used.  As I collect more data, I will update the graphic with a more finalized result.

The Bubble Nebula in HaRGB

The Bubble Nebula in HaRGB

Here’s the bottom line

If you own a Canon DSLR modified for astrophotography, a clip-in Ha filter should be on your shopping list.  I waited far too long before making this decision.  Combining H-alpha exposures to your existing RGB data can greatly increase the amount of detail and contrast in your astrophotos.  This is especially evident in deep-red emission nebulae.

The clip-in versions offered by Astronomik are rather expensive but are a perfect fit for modified or stock Canon DSLR’s.

Update:

In the Summer of 2017, I began using the Astronomik 12nm Ha filter on a one-shot color CMOS camera, the Hypercam 183C.  This time around, I used the 2″ round mounted version of the h-alpha filter.  Although a camera with a mono sensor will perform much better through narrowband filters, a one-shot color camera can still benefit from these narrow wavelengths of light.

Using a Color Camera with a 12nm Ha Filter

The Ha filter factor

The ability to image during the full moon and surrounding week results in much more time under the stars.  No more wasted moonlit clear nights.  If you live in the city, a Ha filter cuts through even the most severe light pollution.  Astrophotography in the backyard becomes possible, and that’s a beautiful thing.

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