Help with processing M51

[Lexi]

Hi all,

So I'm new to astrophotography. I recently tried to image the M51 whirlpool galaxy for the second time (first time around I actually pointed to the right of target and never got anything).

My equipment:

- Skywatcher 200P

- EQ6R pro

- Canon eos 800D (modified)

I imaged around 60 pictures of 2 min exposure each. I had to discard a couple because I live in Denmark and at this time of the year it never really gets dark, so a couple images were too bright.

Total exposure time is then around 1h15min.

I took around 18 darks, and 20 bias, but no flats.

I stacked in DSS and followed some tutorials to edit in Photoshop. I just can't seem to bring out the colors as I see some other have done. I'm sure it's due to my lack of postprocessing skills and possibly also only around 1h exposure.

I'd appreciate it if you guys could give me some tips on both postprocessing and capturing the image.

Thank you.

Attached my attempt at postprocessing and the stacked (.tiff) picture from DSS.

M51_originalStacked.tif

[Budgie1]

I'm not going to be much help with advising the actions you need to take in Photoshop, because I use PixInsight for my own processing, but there are a few tutorials around which will help and I'm sure the more experienced Photoshop users will be along to advise.

In the meantime, I did run my standard workflow with your image through PixInsight and I can assure you that the colours are there and you have good details in there. It would help to use Flats in the stack and there's also the remains of a satellite trail in there (which I removed during processing).

So this is what I managed to get with my basic processing:

Edited May 29, 2023 by Budgie1

[carastro]

I excusively use Photoshop and have a number of video tutorials on You Tube.  Many of them are for Mono imaging but a few of them will be useful to you.  

Before I go any further.   I presume it is too late to take flats, but if your camera is still connected to the scope and not been moved I would stop and take them as these are really essential to a good result.  

Secondly, 2 minute exposurs are a bit short, you really need to be taking 5min exposures.

Galaxies are a bit difficult to drag colour out of.  But using the right processing, you should be able to get some.

This is a link to my website and the various tutorials:

The following may be useful to you: 

Levels and Curves 

Understanding layers 

Processing the RGB might have some useful stuff once you get past the bit on combining the coloured filters (I can't remember as it was a long time ago I recorded this).

Star colour and star reduction may be useful.

Meanwhile I will download your tiff and see what I can do with it.  

https://sites.google.com/view/astrophotography-carole-pope/video-tutorials?authuser=0

Edited May 29, 2023 by carastro

[carastro]

OK I had a play in Photoshop. 

I used levels and curves, balanced the colours, Used the image adjust/match colour a couple of time to increase the colour.  

I had to use Gradient Exterminator because the Vignetting (from not using flats) was starting to encroach.   I can see a dust mote 3/4 of the way up on the right which Flats would have dealt with too. though having said that the optics must be fairly clean.  

I then used selective High pass filter (it should be in my videos), and adjusted selective colour with a little magenta at the end.

HTH

Carole 

[wimvb]

I also downloaded your stacked image. Imo, the data is good, but as said before, you really need to take flats. What's more, you should invest in a good coma corrector. As it is, you have very strong coma, especially on the right hand side. The uneven distribution of coma hints at tilt in the imaging train.

There is some "walking noise" in your image, which you can avoid by dithering. This is a setting you can activate in PHD guiding. Try to dither 10 - 15 pixels on your imaging camera (about 10 arc seconds)

Edited May 29, 2023 by wimvb

[wimvb]

Here's my result, using PixInsight. Most of the process steps that I used are available in PS

- cropping to get rid of stacking edges

- Gradient removal (DBE in PixInsight), two passes

- Background neutralisation. Use the eyedrop colour picker in PS?

- Photometric colour calibration

- BlurXterminator

- Histogram transformation, equivalent to levels in PS

- Colour saturation. Increase overal colour saturation. Then with a lightness mask, protecting the galaxy and stars, decrease saturation in the background

- Noise reduction (NoiseXterminator)

A cropped version less compressed, with colour punch

 

Edited May 29, 2023 by wimvb

[Lexi]

57 minutes ago, carastro said:

OK I had a play in Photoshop. 

I used levels and curves, balanced the colours, Used the image adjust/match colour a couple of time to increase the colour.  

I had to use Gradient Exterminator because the Vignetting (from not using flats) was starting to encroach.   I can see a dust mote 3/4 of the way up on the right which Flats would have dealt with too. though having said that the optics must be fairly clean.  

I then used selective High pass filter (it should be in my videos), and adjusted selective colour with a little magenta at the end.

HTH

Carole 

Thanks a lot Carol. I'm checking out your tutorials they're really good. I really should be taking those flats now when i see those dust specks in your processing. 

[Lexi]

2 hours ago, Budgie1 said:

I'm not going to be much help with advising the actions you need to take in Photoshop, because I use PixInsight for my own processing, but there are a few tutorials around which will help and I'm sure the more experienced Photoshop users will be along to advise.

In the meantime, I did run my standard workflow with your image through PixInsight and I can assure you that the colours are there and you have good details in there. It would help to use Flats in the stack and there's also the remains of a satellite trail in there (which I removed during processing).

So this is what I managed to get with my basic processing:

Wow i think that's quite amazing! I also noticed that satellite trail but i can't really seem to find it in my shots. Guess I need to look closer. Again, very nice processing!

[Lexi]

9 minutes ago, wimvb said:

Here's my result, using PixInsight. Most of the process steps that I used are available in PS

- cropping to get rid of stacking edges

- Gradient removal (DBE in PixInsight), two passes

- Background neutralisation. Use the eyedrop colour picker in PS?

- Photometric colour calibration

- BlurXterminator

- Histogram transformation, equivalent to levels in PS

- Colour saturation. Increase overal colour saturation. Then with a lightness mask, protecting the galaxy and stars, decrease saturation in the background

- Noise reduction (NoiseXterminator)

A cropped version less compressed

Thanks a lot. It looks amazing! I'll try to translate those steps into photoshop.

This might be a dumb question but how do you see that there's strong coma on the right side? Is it the kind of distorted shape of the stars? 

[wimvb]

11 minutes ago, Lexi said:

Is it the kind of distorted shape of the stars? 

yes

Here are sections from your image, taken from each corner, the middle of each side, and the centre of the image. You can see the distorted stars in the corners, especially the right hand side. The stars are a lot smaller in the centre part of the image. Also, the bright star in the lower right corner (main image in my previous reply) has double diffraction spikes. This is caused by either it being a double star (which it isn't) or poor focus. This is a clear indication of tilt.

 

Edited May 29, 2023 by wimvb

[Lexi]

31 minutes ago, wimvb said:

This is caused by either it being a double star (which it isn't) or poor focus. This is a clear indication of tilt.

I see. And this would be corrected by a coma corrector? I did a quick search and could see advanced types with laser and such and also homemade ones made out of old film cannisters. What would you recommend for a newbie?

[wimvb]

1 hour ago, Lexi said:

I see. And this would be corrected by a coma corrector? I did a quick search and could see advanced types with laser and such and also homemade ones made out of old film cannisters. What would you recommend for a newbie?

What you write about here are more likely collimators or collimator caps. Those are needed to align the optical elements in your telescope (tube, primary and secondary mirror, and focuser). Collimation is what you do once every season (unless you move your scope around a lot). A coma corrector is a permanent part of your imaging train. What I mean is this

https://www.firstlightoptics.com/coma-correctors.html

Your telescope may need collimation, which can correct (some of) the tilt. You can easily check if it does in the following way.

Centre your scope on a fairly bright star (Polaris will do). Focus the telescope and make sure that the star is properly centred. Defocus the star untill you see the doughnut shape. Take an image that is not over exposed, ie the star should not be blown out. Move the focuser past best focus and defocus an equal amount "on the other side" of best focus. Take a new image. If the doughnut ring is even and symmetric in both images, the optics are aligned. If the dark centre of the doughnut is more on one side, alignment is off, and you will need to collimate. Collimating an f/5 Newtonian is a bit fiddly first time you do it, but it's not too difficult. There are many guides online. You only need a few tools.

Edited May 29, 2023 by wimvb

[Lexi]

17 hours ago, wimvb said:

What you write about here are more likely collimators or collimator caps. Those are needed to align the optical elements in your telescope (tube, primary and secondary mirror, and focuser). Collimation is what you do once every season (unless you move your scope around a lot). A coma corrector is a permanent part of your imaging train. What I mean is this

https://www.firstlightoptics.com/coma-correctors.html

Your telescope may need collimation, which can correct (some of) the tilt. You can easily check if it does in the following way.

Centre your scope on a fairly bright star (Polaris will do). Focus the telescope and make sure that the star is properly centred. Defocus the star untill you see the doughnut shape. Take an image that is not over exposed, ie the star should not be blown out. Move the focuser past best focus and defocus an equal amount "on the other side" of best focus. Take a new image. If the doughnut ring is even and symmetric in both images, the optics are aligned. If the dark centre of the doughnut is more on one side, alignment is off, and you will need to collimate. Collimating an f/5 Newtonian is a bit fiddly first time you do it, but it's not too difficult. There are many guides online. You only need a few tools.

Thanks a lot for the clarification.

[Lexi]

Hi again,

So I downloaded a free trial of Pixinsight and followed some tutorials. It took me a couple of days of trial and error to come up with the following result. I also ended up discarding a lot of the pictures I took, leaving me with 45min of stacking. Definitely not on same level as you guys but it's a start.

I must say I really like the work flow process in Pixinsight  I find it more intuitive than Photoshop. I might get a license when my trial period expires.

Regarding the line that looks like a "satellite": I actually found this line on each of the shots. I have no idea what it is...

But I will definitely get out there again,  this time make sure I get those flats.

[wimvb]

4 minutes ago, Lexi said:

I might get a license when my trial period expires

You won't regret it.

On my handheld screen the background looks a bit green. Try scnr (processes >> noise reduction) with standard settings.

[Budgie1]

For your first exploration into PixInsight, I'd say you've done well. Compare this new image with your first one!

As Wim says, a little SCNR green removal would help with the background, I would probably go with 0.70, rather than the default 1.00, just so you don't remove all the green in the image.

You can also have play with the CloneStamp tool (Processes > Painting) to remove that line and the dust mote. Go with a good size radius, softness at 0.70 & opacity at about 0.50 and just take your time.

[Lexi]

Thanks for the tips guys. I think I got rid of the greenish tinge. I also attempted to use the clone stamp tool so remove the line and the dust mote. I definitely need more practice. But overall I'm satisfied,

I really appreciate all your help. My eyes have been opened to the power of pixinsight. Hopefully I can get out there soon and image again.