M51 but why no Ha ?

[Roy Foreman]

Shot this over two nights and just 1 hour of exposure time in 60 sec subs.  Telescope was a 16" F/4.5 reflector, camera a ZWO 6200 full frame, and a UV/IR cut filter.

The image is reasonably ok, but there is little if any Ha showing up at all.  The camera is sensitive to Ha, and the UV/IR cut filter should let it pass, so where has it got to?

Does it need a separate, much longer, exposure through an Ha filter to bring out all those red knots of Ha that I know exist in the spiral arms ?

The reason I am puzzled is that I imaged this galaxy a couple of years ago using the same setup but with a Nikon D810a astro DSLR,  and there was more Ha showing with much less exposure time (10 or 20 mins I think)

Any ideas ?

 

 

[vlaiv]

They are there - but are discolored due to whole image having a strong blue cast.

Here is your image:

I marked some features out Ha regions are marked with an arrow, while prominent features are circled (one star and one star field)

Same features marked on reference image.

Now look at color cast in your image compared to reference:

It's like you boosted blue too far - galaxy cores are no longer yellow and there is no red to speak of

[Debo]

I tried fiddling with the colour saturation, it seemed your original had very little 🤔

 

Edited May 1, 2022 by Debo

[Debo]

[Roy Foreman]

Thanks very much for that guys, I do appreciate the help.  So it seems its down to my processing. I did actually boost the saturation by what I thought was quite a bit, but did very little to the colour balance out of the camera.

Now that I know the data is in the image I will have another go.

Once again, thank you both for your assistance.

[Laurieast]

My version for what it's worth, had to pull up the saturation a lot.

[Roy Foreman]

Here's version two with more aggressive processing. Very quick reprocess, when I get more time I will have another go.

Thanks once again.

 

 

[Roy Foreman]

4 minutes ago, Laurieast said:

My version for what it's worth, had to pull up the saturation a lot.

Looks like you've managed to pull out some extra detail from the image as well.  More for me to work on.

Many thanks for your input on this.

 

[Laurieast]

Do you stack in Deep Sky Stacker? That seems to reduce the colour depth for me, but so does Affinity.

[Roy Foreman]

Tried both and Affinity works best, which is what I used for this image. I agree that both reduce colour depth, and best colour seems to come from stacking manually in photoshop, but that's a bit of a faff for anything more than a dozen or so images !