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How a DSLR Ha Filter can Improve your Astrophotos

DSLR camera Ha filter
|H-Alpha|11 Comments

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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This Post Has 11 Comments

  1. Darryl Ellis says:

    Hi Trevor,

    Awesome site, outstanding pictures, and I appreciate your openness and willingness to share your hard earned experience. I am a one year old when it comes to AP, and I too image from a Red Zone with an XSI through a refractor.

    I am slowly getting my equipment together and recently upgraded to a decent mount, a CGEM DX, though my camera is yet unmodified and my telescope is a simple C80ed.

    I plan to do the full spectrum mod soon however, but thought that I needed the CLS CCD to block some of the IR necessary to focus with a refractor. I plan to follow your advice also about using the HA filter, but can I use it alone?

    Thanks,

    Darryl

  2. Trevor says:

    Thanks, Darryl! Nice to hear that you are resilient in your efforts against light pollution. I use the IDAS LPS clip-filter by Hutech for LP (it also protects the sensor) for my regular RGB imaging – And then I swap it out for the Astronomik 12nm Ha filter when imaging Hydrogen alpha. I would recommend getting the CLS (clip-in version) filter before doing the full spectrum mod. I’m very happy with the Astronomik filter – well worth the money:) Cheers!

  3. Danny Jones says:

    Hi Trevor,

    I have a 5D MKII, unmodded. So will this filter help with my imaging in the heart of Edmonton? (A complete red zone). So far the images I have been getting are washed out white glowish messes, with a DSO somewhere in the frame. IF I was to add one of these clippable filters, would it help eliminate that whiteish glow? I would love to get the Camera modded, but there is no way I am capable of modding it, I would destroy the camera in about 30 seconds haha. Also, you mention Ontario Telescope sells these filters, but I can not see them on their site. Do you have a link to the purchase page? Thanks, and keep it up, your site has been so helpful. the tutorials are amazing.

    Cheers,

    Danny

    Ps. I am using an 8″ EdgeHD.

    • Trevor says:

      Danny, so sorry for the late reply. Light pollution filters and narrowband filters are a MUST from a light polluted area like Edmonton. I’ve found that by shooting RGB images with a light pollution filter such as the Skytech CLS-CCD – and adding images in ha (using the Astronomik 12nm Ha Filter) – you can really get some amazing results from a red/white zone. OTA does not currently sell Astronomik filters – I bought mine from OPT in the States. Clear skies man.

  4. Diego Gomez says:

    Hello Trevor,

    I wondered if you could please share tips/experiences on how you achieve focus using NB filters? I have read in several threads that it’s quite complicated because you basically can’t use Live-View mode unless you focus first on a bright star like Vega.

    Thanks in advance,
    Diego

    • Trevor says:

      Hi Diego. As you mentioned – focusing on a very bright star is helpful. Ideally, you’ll use a bright star that is nearby, lock your focuser – and then slew to your target. Taking short text exposures (Say 5 seconds at ISO 3200) is helpful too, and then you can make small adjustments between each test shot. It is a bit of a pain – but well worth the effort in the end!

  5. taylor wilson says:

    Hi,
    I’m trying to find more information about the H-Alpha conversions that I see offered, or more specifically, if they’ll be of any use to me. I don’t use telescopes or anything to shoot deep space astrophotography. I just shoot standard astrophotography, usually with a 14mm wide angle lens. what I’m not sure about is if the h-alpha conversion would help me, or is it really just for people shooting deep space. any input would be greatly appreciated. Thanks!

  6. jack sharp says:

    If you want to drizzle with DSS and you have a x64 processor and 8Gb+ of Ram…..you need to use the “large address aware memory tool”. This allows DSS to use up to 4Gb of your Ram. I followed the instructions in this link:
    https://www.techpowerup.com/forums/threads/large-address-aware.112556/
    and was able to perform a 2x Drizzle.
    As with any tweaks to software/OS do this with caution. 🙂
    …..if you were to use PixInsight…….Drizzle Integration is built in 😉

  7. Paul Bennett says:

    Thank-You for the write up, just bought the Baader Ha & S-II 2″ filters to use with my Nikon D5300, as I only use this camera now for AP I will take out the hot-mirror myself again and go naked sensor. what filter would you recommend for my color shots, I did once try the Idas-P2 but had big problems with reflections with that filter, something I’ve not had with my Baader filters, I do have the Baader Skyglow and the UV/IR-Cut/L to try but just wondered what filter you use.
    Thx Paul

  8. Sokratis Papageorgiou says:

    Trevor: I have an Ha filter but also an Hb as well. Both Astronomik clip ons to my modified Canon D70. Is it worth using the Hb along with the Ha? Not together of course but on different nights to collect more data. For the RGB photos should I just use a CLS or UHC? I am currently imaging IC434 and noticed that my Hb images are coming out very blue. I have not yet overlayed the Ha images on top of the Hbeta. I did notice however that the Halpha images had much more detail to them. What is your ideal method given the filters I already have? Should I be getting another filter to add the collection? Also wanted to mention I really enjoy your videos.

  9. Daniel says:

    Great article … am looking into getting one of these now to help with nebula work.

    Just curious, as I also have a solar filter which goes over the end of my scope (and conveniently same size as my tele lens hood), could this Ha filter work to show Solar prominences and details on the Sun? I’ve been shooting the Sun in just white light and wanting more detail. Do you have any examples of shooting the Sun with this filter?

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