Help with stacking & processing.

[CraigD1986]

I had a couple of unsuccessful nights of trying to image M31 and would be grateful for any help or advice as I'm a little stuck. Here is my setup

Sky watcher star adventurer, Canon 5D Mk IV with Sigma 150-600 @ 400mm.

f5.6, ISO 2500, 60 seconds.

I made a mess of the darks (f6.3) so had to discard these, forgot to do flat frames but did remember the bias frames.

I thought I would try to salvage what I had so stacked the good lights and bias frames in DeepSkyStacker. I had 52 light frames and 20 bias. I set the star detection threshold to 64% (108 stars) and the below screenshot shows the result. First off, I'm not sure why the image is so blue or why there is a huge blue haze from the right. Also note the histogram. I can't even start stretching this as the data is all on the way to the left.

I've obviously made a few errors here but can't figure out what (aside from not having any darks or flats). Is anyone able to advise?

Many thanks in advance!

[alacant]

2 hours ago, CraigD1986 said:

forgot to do flat frames

Hi

I think the sigma may have click stops for orientation. If so, just replace the camera and take the flat frames. You may be lucky. It's very difficult to process without.

The f-ratio is irrelevant for dark frames but lose them anyway with recent eos'.

Go easy(ier) on the background.

Post -a link to- the stack if you like. 

Cheers

Edited October 7, 2021 by alacant

[Jp114]

The first time I used DeepSkyStacker I opened my darks with my lights using "Open Picture Files", instead of looking at the line below, which is "Dark files" (Bias is two lines below).  Needless to say, the image wasn't great...

Is there a chance you've done the same?  It might be worth trying it without Bias frames, just to see what happens.

Regarding the darks, did you discard them because of their focal ratio (f/6.3 vs f/5.6)?  If so, as long as the time and temperature match your light frames they'll be fine.

Jon

[Jerry Barnes]

I think if you pull the mid point of the histogram down first (move it left) you will start to see space on the left of the histogram to allow you to move the left point upwards.  Is that what you meant?

Jerry

[AstroMuni]

19 hours ago, CraigD1986 said:

Also note the histogram. I can't even start stretching this as the data is all on the way to the left.

Is this just the stacked image or have you done any stretching? Please post the stacked image before stretching like Alacant suggested and you should soon get suggestions

I do get the blue glow from my astro camera due to amp glow. Guessing its a similar issue with camera sensor. Once you take the darks they should cancel that out.

Edited October 8, 2021 by AstroMuni

[jacko61]

Isn't ISO 2500 rather high?  I've found in the past with my 70d that anything beyond ISO 800 the objects get blown out and there's too much background noise.

Graeme

[Richard_]

I haven't used DSS for quite some time so please forgive me if I'm wrong. Did you shoot your images in RAW? If so, what bayer pattern did you choose in DSS for the debayer process? It should be RGGB.

[CraigD1986]

Thanks everyone for the replies and help.

I did keep the dark files but assumed I couldn’t use them. That’s good news then so I’ll re-stack using those files.

I added all the image in the correct place in DSS (Double checked) and the image above is the auto save TIFF file with absolutely nothing done to it.

Re: ISO… anything less than 2500 was clipping the blacks.

I can’t remember what bayer pattern I used but I will have used all default settings as I’m new to DSS. All images were shot in RAW.

I’ll re-stack and try all of your suggestions tonight.

Thanks again guys. I’ll report back when I have a chance to take another look.

[Padraic M]

The Astro processing Tool (APT) Canon matrix lists 1600 as the best ISO for 70D. 

https://astrophotography.app/EOS.php

I don't think a low ISO will clip the blacks, it just won't gather as much light so you'll need more exposure time.

[CraigD1986]

27 minutes ago, Padraic M said:

The Astro processing Tool (APT) Canon matrix lists 1600 as the best ISO for 70D. 

https://astrophotography.app/EOS.php

I don't think a low ISO will clip the blacks, it just won't gather as much light so you'll need more exposure time.

Thanks for the link. I was already at 60 seconds unguided on a star adventurer so any longer at 400mm was creating star trails. I’ve just preordered an ASiAir Plus with guide scope and camera though so I hope to increase that exposure time in the near future.

[Padraic M]

19 minutes ago, CraigD1986 said:

star trails

No problem 🙂 ! More exposure time can be longer subs or more subs at 60s.  Guiding does make things easier though and gives you more options.

Be careful, I sense you've started down that slippery slope....

[Elp]

Iso of 2500 seems high especially for 60 seconds, last time I was shooting Andromeda I was doing 9 second exposures at iso 1600. I did take over 300 images though. My stacked histograms are usually skewed to the left but are not clipped (there's room to move the black levels over).

Using a Canon myself I haven't seen an option in DSS to choose a Bayer pattern (its not something I need to do), I normally have to convert the CR2 raw files my camera produces into TIFF before I can stack in DSS, do you have to do the same?

At first when I saw your posted image it looked like amp glow but Ive never seen anything like that from my dslr, after that it looks like some sort of light pollution but I don't know what your imaging conditions were like at the time (I've shot images where lampost light is not in frame but affects the stack as a gradient in the image).

[CraigD1986]

I've just tried re-stacking and at 9% threshold, DSS detects 1870 stars when when I go to stack, I now get an error saying "only one frame will be stacked. You should check/change the star detection threshold to detect more stars..."

I use the CR2 RAW files straight from the camera.

I'll have another look at my exposure settings next time I go out but for the moment, I seem to be struggling with the stacking process.