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H-Alpha

Short Nights and Hot Sensors

|Nebulae|2 Comments

The hot nights of early summer astrophotography start late and end early. The warm temperatures at night make their presence known in my DSLR images in the form of noise.

My telescope in the backyard

My latest deep sky project involves capturing data on NGC 6888 in H-Alpha with a DSLR.  My highly portable astrophotography equipment allows me to move the entire rig around the yard based on my imaging target.

This month, I have been getting a head start on summer Astro targets in Sagittarius such as the Omega Nebula. This means waiting until after midnight for my targets to rise high enough in the Southeast for a clear view.

The Canon Rebel T3i is back in action!

Despite the glow of the full moon and nightly “lows” of 27 degrees Celsius, I have continued to fire away at the night sky with my modified Canon DSLR.





H-Alpha with a DSLR: Crescent Nebula

Crescent Nebula in H-Alpha

The Crescent Nebula in H-Alpha

The subject of my most recent outings is NGC 6888 in Cygnus, the Crescent Nebula. With an Astronomik 12nm ha filter installed in my Canon 600D, I have captured over 3 hours worth of data on this striking emission nebula.

My version of NGC 6888 is just starting to show the fainter details of the nebula.  A deeper view like this one featured on Astronomy Magazine shows the delicate structure of this deep sky object.

Canon Rebel DSLR for astrophotography

As I mentioned earlier, these were HOT nights.  The temperature of the camera sensor was well over 30 Degrees Celcius for most of these images.  This is quite a drastic contrast between the chilly images I captured last month using the icy ASI071MC-Cool.

The Crescent Nebula in H-Alpha

Total Integrated Exposure: 3 Hours, 10 Minutes (26 frames)
Captured over 2 nights using a modified Canon Rebel T3i/600D and Astronomik 12nm Ha Filter.

Imaging Session 1 – June 10

Canon T3i @ ISO 800
300-second subs

Imaging Session 2 – June 11

Canon T3i @ ISO 1600
300-second subs

The Crescent Nebula is a notoriously difficult deep sky target from light polluted locations.  Those shooting with a stock DSLR may be disappointed by the lack of structure captured using modest exposure lengths.  Dark skies and hour of data are essential to produce a detailed portrait of NGC 6888.

Image Processing (Video)

The video below has been sped up to show you the basic image processing steps I took in Adobe Photoshop.  The image starts out as the RAW stacked file produced by Deep Sky Stacker – and is processed using levels, curves and specific actions from the Astronomy Tools Action Set.


Collecting Color (RGB) Data
Astronomik 12nm Ha Filter

This Ha data will later be combined with upcoming true color RGB photos to produce an HaRGB composite in Photoshop. The hydrogen alpha details in the Crescent Nebula should help boost contrast in the final image.

To combat the thermal noise in my images, all I can do is limit the ISO sensitivity when shooting, and apply dark frames when stacking in Deep Sky Stacker.

As expected, the RAW images out of the camera were incredibly noisy. Stacking multiple images and subtracting darks certainly helped, but it does not correct the issue completely.

This is precisely why I am so interested in the capabilities of the Altair Astro Hypercam 183C, and how the Sony IM183 sensor will perform.

The Hypercam 183C will take over as my primary imaging camera starting this week

The nebula looks gorgeous in Ha, but what about color? Below is an example of this target using a stock digital camera in full color.

NGC 6888 through a stock Sony A6300

A member of the AstroBackyard Facebook page recently shared his image of the Crescent Nebula using a stock Sony Mirrorless digital camera.  This is a great example of what to expect using a stock Sony A6300 for astrophotography.

Sony A6300 for astrophotography

NGC 6888 using a Sony A6300 mirrorless camera




Zhonghua was able to pull out some impressive detail and color in this faint emission nebula with his stock A6300. This was captured through a Celestron NexStar 6SE telescope on a custom built wedge mount.

The image above shows the Crescent nebula in true color, which I will be adding to my original H-Alpha image for an HaRGB composite.  This way, I am able to show the nebula in true color, while benefitting from the additional contrast and detail in the hydrogen alpha wavelength.

The Summer Triangle

The constellation Cygnus, including NGC 6888 is a part of an asterism in the night sky known as the “Summer Triangle“.  This triangle of stars consists of Altair, Deneb, and Vega.

By mid-July, these imaging sessions will commence when the night has set in at about 10:30 pm.  I enjoy watching the Summer Triangle continue its approach into my backyard viewing window night after night.

The summer triangle

The Summer Triangle consists of Altair, Vega, and Deneb

Anything I photograph in this region is arguably the darkest and clearest area of the sky from my backyard.  The photo above was shot through heavy light pollution using a wide angle camera lens. Through careful image processing, I am able to restore the details of this dense region of the Milky Way.

Testing the Hypercam 183C

The highly anticipated Hypercam 183C astronomy camera will be arriving this week. Although the CMOS IMX183 sensor is not cooled via TEC-cooling, it benefits from an internal fan and a design that maximizes air flow.

Altair Hypercam 183C

You can expect some color images of the Crescent Nebula using the 183C in the coming weeks.  The team over at Ontario Telescope and Accessories have assured me that 183C is on the way!

The 20MP sensor housed in the Hypercam means that the resolution will exceed the current size of my Rebel 600D image frames.  Some scaling will be required to match the images up in the image processing stage

Please join the AstroBackyard Newsletter to stay up to date with my latest equipment reviews and imaging techniques.

Related Video: Processing H-Alpha in Adobe Photoshop



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How a DSLR Ha Filter can Improve your Astrophotos

|H-Alpha|3 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.

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 an 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 Canon 450D and a 12nm Ha filter

 

Canon DSLR with Ha Filter - 12nm Version Example Image

Results from a Canon 450D with a 12nm Ha Filter

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 neary 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.

 


 

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.

 

6nm Ha filter for Canon DSLR

The 6nm Ha filter from Astronomik

 

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 an 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.

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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