First attempt at M51 Whirlpool Galaxy with new scope

[Adam1234]

This is my first attempt of M51 the 'Whirlpool Galaxy', and also the first time using my new mount & scope (SkyWatcher EQ6-R Pro and SkyWatcher ED80 DS-Pro). Polar alignment with QHY Polemaster wasn't perfect (when I did the axis rotation I couldn't get the chosen star to exactly on the green circle) and I haven't got a field flattener yet, waiting for that to arrive.

I managed to get 80 x 3 minute lights unguided with my Canon 2000D at prime focus with Optolong L-Pro Broadband light pollution filter, 20 x darks, 40 x bias, 36 x flats and 40 x dark flats, stacked in DSS and processing in photoshop. Total exposure 4 hours.

I cropped the image slightly as I had a horrible dark and grainy gradient on one side of the image when stretching, but couldn't crop too much either or it became too pixelated. 

 

Hope you like.

Adam

 

Edited March 29, 2020 by Adam1234

[Anthonyexmouth]

I always find M51 too small a target for my ed80, still a nice pic. M101 fills the frame a little better. 

 

Also, I think using bias and dark flats together can be detrimental to the stacking. dark flats are the way to go with a CMOS sensor

[Pankaj]

Beautiful. There's a lot that can be done with this small little scope. Best part is its wide FOV. Try 31 next time. It will fill the frame. This image I shot with Orion ST 80 on NEQ6 without guiding.

[alan potts]

That's come out nicely considering it is so small, I have never tried this one.

Alan

[Adam1234]

36 minutes ago, Anthonyexmouth said:

Also, I think using bias and dark flats together can be detrimental to the stacking. dark flats are the way to go with a CMOS sensor

How come together they can be detrimental? 

[Adam1234]

15 minutes ago, Pankaj said:

Beautiful. There's a lot that can be done with this small little scope. Best part is its wide FOV. Try 31 next time. It will fill the frame. This image I shot with Orion ST 80 on NEQ6 without guiding.

M31 is now too low on the horizon for me, but I'll be definitely imaging it next time it comes around!

[Anthonyexmouth]

1 minute ago, Adam1234 said:

How come together they can be detrimental? 

I'm not sure of the technical reason, but far more knowlegable people here have said that CMOS are better calibrated with dark-flats. bias and dark-flats are doing the same job i think and using both causes issues. 

[Adam1234]

1 minute ago, Anthonyexmouth said:

I'm not sure of the technical reason, but far more knowlegable people here have said that CMOS are better calibrated with dark-flats. bias and dark-flats are doing the same job i think and using both causes issues. 

Ah ok!  I've now decided on doing an experiment and going to stack:

- only light frames

- lights + darks

- lights + flats 

- lights + flats + dark flats 

Will be interesting to see what the result of each combination gives, and might help to see if my calibration frames are any good!

[MarkAR]

53 minutes ago, Adam1234 said:

Ah ok!  I've now decided on doing an experiment and going to stack:

- only light frames

- lights + darks

- lights + flats 

- lights + flats + dark flats 

Will be interesting to see what the result of each combination gives, and might help to see if my calibration frames are any good!

Also post process them all the same, would like to see the results.

[Adam1234]

24 minutes ago, MarkAR said:

Also post process them all the same, would like to see the results.

Good idea, I'll do exactly the same to each, and post the resulting images

[Adam1234]

Done some very quick and very crude processing in photoshop, literally just aligned the RGB channels by adjusting the levels slider for each channel, a bit more levels and a couple curves adjustments. Done exactly the same for all images (done all the adjustments on the 'lights' image and copy and pasted the adjustment layer to the other images so everything was the same). No cropping, and no other adjustments except simple levels and curves.

My first thoughts are that I can definitely see why flat frames are a must!!! Vignetting is very much reduced and the field is a lot flatter. Stretching the images without flats seems to produce coloured rings around the image (not so much visible in the jpegs but VERY visible in the when working on the .tif file.

Struggling to pick out what effect the dark frames are having (aside from the background colour) in terms of noise, maybe a seasoned expert with a keen eye might be able to tell if the dark frames are reducing noise or just adding to it.

 

Here are the (very crude) results of my experiment:

Light frames only:

 

Light frames + Dark frames:

 

Light frames + flat frames:

 

Light frames + flat frames + dark flat frames:

 

Lights + darks + flats + flat darks:

 

Adam

 

[MarkAR]

Great experiment.

Looks like flats are the greatest benefit visually, darks and dark flats just reducing any sensor noise which on the uncropped image doesn't really show up.

Thank you for taking the time.

[Erling G-P]

Yes, very illustrative and most interesting! 👍

[gilesco]

You definitely need the flats. I think your darks are adding future processing potential to the frames too.

I'm not sure about the rest, I have a CMOS camera, and use bias, flats & darks myself.

[alacant]

Hi.

With DSLRs I find that dark frames introduce more noise.

The best combination I've found is to 

1. Dither between each light frame.

2. Subtract the stacked master bias from both the light and flat frames.

3. Stack the flat frames and then calibrate each light with the master flat.

4. Register the calibrated light frames.

5. Stack the calibrated light frames using a sigma clipping algorithm.

The best software I've found that does this (or whatever you tell it to do) and nothing else is Siril.

HTH

[vlaiv]

On 29/03/2020 at 18:13, Adam1234 said:

Lights + darks + flats + flat darks:

Add bias in the mix and use dark optimization, and you should theoretically get best calibration with camera that has not got set point temperature regulation.

[Adam1234]

I got another 4 hours worth of 180s subs last night on M51 (+darks, flats, dark flats) and stacked these with last weeks subs, to now give a total of ~8 hours 🙂

I think the extra 4 hours has improved the image a bit? Debating whether or not to try and get a few more nights data, or start imaging something else.

 

Same image but cropped slightly

 

Adam