Ha Filter is worth it on DSLR

[johneta]

I wanted to post my experience with an Ha filter and a DSLR Camera.

I had thought about getting an Ha Filter for my Modded 550d for a while, and the only real positive comments I'd seen for it were from Trevor at Astrobackyard.

Most other Discussions around forums, talked about the issues with loosing so much signal via the green and blue filters over the sensor and only getting 1/3 (1/4?) the amount of light a Mono cam would get. Thus rendering it really a waste of time.
But if you're like me, and not ready to fork out the big bucks on a Mono cam, and you already shoot with a DSLR, then I can confirm that, despite the science, - it does work well.

Judge for yourself:

First image is 1 light of the Carina area -  550d, Pentax 200mm lens at F6.1, ISO 800, 300secs

Second image is 1 light with a ZWO 7nm Ha filter. F4, ISO1600 300secs
(Note: the filter is the old type that is known for halos around bright stars-but I didn't find it too bad in this image)
(Also Note.. ignore the blown out core--Photshop RAW does something weird with these red only images, but they open fine in the image stacker of your choice)

As you can see above, I increased the light gathering on the second image, but it seems brighter than the first image, so I think I could have easily gone down to ISO800

I half expected that I would open the shutter for 5minutes and get virtually nothing at the end, but I was amazed to see so much signal from my little old DSLR.

So if you were wondering if its worth it-- well I think it is!

Two Caveats though.....
1.  My plan was to use Ha as a luminance layer and boost the faint areas of Nebulosity. - But it's surprisingly difficult to do, and keep natural colours.
I ended up doing the best Processing I could with just the regular colour image. Then I added the Ha as a Luminace layer on the colour image and revealed the faint stuff and detail.
This HaRGB image had great detail but was a pastel soft pink colour, which was very hard to change.
SO in PS I had 2 layers -HaRGB image on the bottom and RGB image on the top layer. I then painted in just the faint stuff from the HaRGB image onto the RGB image. This kept the majority of the image natural looking and the faint stuff blended into this quite nicely.

2. This is my first outing with the filter and I chose the Carina Nebula. This is an EASY target!  It's super bright, and as most Southern Hemisherer's will know, a reasonable length image gives you a dazzlingly bright picture. Like daytime photography 🙂       -- So further tests on dimmer targets will be interesting.

Edited July 18, 2020 by johneta

[pete_l]

Excellent work!
It illustrates perfectly the old adage of "those who say it can't be done should keep out of the way of people doing it"

 

[Snoani]

Nice post John and I very much appreciate it.  It will be a year or two before I purchase an astro camera and so I am considering (highly likely to) buying a H-alpha filter in a couple of months to use with my DSLR. 

Jem

[alan potts]

Nice images and nice report, I am sure some will find it very useful, do like Trevor and his backyard, I have learnt a lot from him.

Alan

[johneta]

Hey thanks guys, I hope it does help people decide either way.   -Yes I enjoy Trevor's channel- always a snippet or two of inspiration in there.

Good luck Snoani if you get the new piece of kit

[ollypenrice]

I think that there is plenty of evidence 'out there' to show that Ha does work on modded DSLRs despite the loss of efficiency. There are lots of red filtered pixels on your chip, after all.

Regarding processing, at one time imagers regularly used Ha as luminance and regularly produced very pink nebulae dotted with stars with large blue haloes.  The problem is simple: Ha filters pass deep red light so it cannot be a good idea to illuminate an entire image, including the green and blue parts, with such light. There is a much better way in which you apply the Ha where it belongs - in the red channel.

Process your natural colour image and Ha image independently. If you're going to use the Ha image only as a component within the colour one you can push it very hard for high contrasts and not worry about a little noise in the dark parts because they won't be present in the final blend. In Ps, split the colour channels and paste the Ha onto the red. Change the Blend Mode to lighten. Now the Ha will be applied to the red only where it is brighter than the red. If you want to see if you can push the Ha still harder in this mode give it a try in Curves. Hold the bottom of the curve down and lift the upper parts a little, all the while looking at the result. Flatten the Ha onto the red and merge the channels.

If you feel the new HaRGB has too much Ha contribution simply paste it on top of the RGB original and dial down the opacity to taste.

On some images a tiny hint of Ha as luminance may be helpful but I never apply it beyond 15% opacity.

A final tweak to bring out Ha regions in Ps can be done in Selective Colour. Simply move the top slider in Reds to the left to lower the cyans in red. This makes the Ha pop.

Olly

[johneta]

Thanks Olly
I did briefly try just using Ha for the red channel(or mixed in with the red channel), and didn't like the different red hue it created. But I didn't give that much time.
I concentrated on the Luminance end of processing. I will give the Ha/Red a good try soon.

I had seen your similar posts on your technique there, and description of the salmon pink colour that results from full-on Ha Luminance.
I had hoped that the detail and contrast gained with the Ha image would magically enhance the whole image , but alas that cant happen without some drawbacks.
I need to use it with more subtlety as you suggest.

[R26 oldtimer]

I consider an Ha narrowband filter a must for a modified dslr. And don't forget that you have only a 1/4 of the pixels capturing signal, but you get almost four times more sensor size than most mono dedicated cameras. Now, I think I've just opened this week's can of worms! 🤣

[ollypenrice]

5 minutes ago, R26 oldtimer said:

I consider an Ha narrowband filter a must for a modified dslr. And don't forget that you have only a 1/4 of the pixels capturing signal, but you get almost four times more sensor size than most mono dedicated cameras. Now, I think I've just opened this week's can of worms! 🤣

If you've got four times this sensor size you have one almighty chip! 😀 But, more seriously, your pint is perfectly sound.

Olly

[johneta]

I somehow missed this positive sentiment when I was thinking about getting the Ha filter. 

Also the day after posting this I saw a whole lot of Ha, and Ha OIII DSLR images on Astrobin 🙄