Another M51

[GraemeH]

Looking at lots of posts recently with spectacular images of M51 - seems that the whirlpool is very much in vogue right now.  For my part, I was fortunate to get an unexpected couple of hours of clear sky earlier this week and grabbed what is by some distance the best collection of data I have achieved so far in my short time doing DSO imaging.  I've posted this image already in the Galaxy challenge, but thought I'd share here too because I'm hoping for some constructive criticism.  I'm also sharing the unprocessed, uncropped TIF from DSS because I'd love to see if there's more to uncover in my data that requires a higher level of skill in processing than I currently have.  It would be great to see what some of you fantastic people can get from it.

Thanks for looking.

Graeme

Autosave001 (1).tif

[michael.h.f.wilkinson]

Nice one! What kit did you use?

[celestron8g8]

Very nice capture ! M51 is an awesome galaxie just by itself but in a WF such as this one you also captured it's companion . I'm on a work computer so I have no access to give the ID# but this is a big plus ! Thanks for sharing !

[feilimb]

Graeme that is simply stunning, I love the detail and colour range you have achieved there.  Absolutely love it.

I shot M51 a couple of nights ago @ 510mm (Skywatcher 80ED) on a DSLR and am hoping to process it tonight, but the scale you have here is fantastic (in my case the galaxy will be pretty tiny in the overall field of view).  What focal length / F-ratio were you at here, and how many minutes of subs were integrated?

[GraemeH]

Sorry folks - I forgot to add the acquisition details.

This is a crop from a stack of 26 lights (300", ISO1600) from my Canon 6D calibrated with flats and bias. No darks. Taken through EdgeHD8 on a wedge mounted Nexstar Evolution, guided by PHD2 using Qhy5lii-C through Celestron OAG. DSS for stacking, photoshop cc 2018 for processing.

[GraemeH]

27 minutes ago, celestron8g8 said:

Very nice capture ! M51 is an awesome galaxie just by itself but in a WF such as this one you also captured it's companion . I'm on a work computer so I have no access to give the ID# but this is a big plus ! Thanks for sharing !

Thank you.  The other galaxy to the right of the field is IC4263, and according to my astrobin platesolve, I also have IC4278 as a faint smudge at the extreme left of the field.  I had no idea of the existence of either before processing this one. 

[celestron8g8]

2 hours ago, GraemeH said:

Thank you.  The other galaxy to the right of the field is IC4263, and according to my astrobin platesolve, I also have IC4278 as a faint smudge at the extreme left of the field.  I had no idea of the existence of either before processing this one. 

Look at this image of M51 by Robert Gendler . Choose as big an format as you can and you'll see lots of smudges all around M51 . 

http://robgendlerastropics.com/M51NM.html

 

[ollypenrice]

You have a very good result. I would have two immediate priorities for taking the image further. Firstly I think it is a bit colour cold, so a bit on the blue side. I think the reds might need a slight lift.

Then the background sky is rather 'busy.' A large dither - 12 pixels or so - between subs will greatly reduce colour mottle in DSLR images. Using normal noise reduction which uses pixel-to-pixel communication will probably introduce the 'oily' look which is unattractive. Dither is the best way with DSLRs.

Rob Gendler's image is a benchmark but note the exposure time and the apertures used - and bear in mind that his processing expertise is at the top end of world class.

Olly

[GraemeH]

14 minutes ago, ollypenrice said:

You have a very good result. I would have two immediate priorities for taking the image further. Firstly I think it is a bit colour cold, so a bit on the blue side. I think the reds might need a slight lift.

Then the background sky is rather 'busy.' A large dither - 12 pixels or so - between subs will greatly reduce colour mottle in DSLR images. Using normal noise reduction which uses pixel-to-pixel communication will probably introduce the 'oily' look which is unattractive. Dither is the best way with DSLRs.

Rob Gendler's image is a benchmark but note the exposure time and the apertures used - and bear in mind that his processing expertise is at the top end of world class.

Olly

Thank you so much for the feedback Olly - some of your tips on other images have already been very helpful to me in gaining some idea about what I'm trying to achieve. 

I do use dithering, but perhaps I need to increase the scale a bit. My current settings tend to give around 4-5 pixels movement between subs so I'll certainly change that the next time there's any break in the cloud cover here in central Scotland. 

I'll have a try at boosting reds a little bit with my next reprocess, but to be honest your comment that I have a good image has made my day. I feel a bit like a kid who's been given a gold star by the teacher! 

[ollypenrice]

7 minutes ago, GraemeH said:

Thank you so much for the feedback Olly - some of your tips on other images have already been very helpful to me in gaining some idea about what I'm trying to achieve. 

I do use dithering, but perhaps I need to increase the scale a bit. My current settings tend to give around 4-5 pixels movement between subs so I'll certainly change that the next time there's any break in the cloud cover here in central Scotland. 

I'll have a try at boosting reds a little bit with my next reprocess, but to be honest your comment that I have a good image has made my day. I feel a bit like a kid who's been given a gold star by the teacher! 

Heheh, well maybe I felt the same when Rob Gendler gave our latest M51 an 'excellent' on Facebook yesterday! This is a supportive community - which is great. 

Olly

[tooth_dr]

1 minute ago, ollypenrice said:

Heheh, well maybe I felt the same when Rob Gendler gave our latest M51 an 'excellent' on Facebook yesterday! This is a supportive community - which is great. 

Olly

Well done Olly!

Can I ask this - can you over-dither? Yes you will lose some of your imaging field but can it be detrimental in other ways if you dither say 20px? Also would you suggest random or spiral dithering?

[GraemeH]

On ‎22‎/‎03‎/‎2018 at 19:37, ollypenrice said:

You have a very good result. I would have two immediate priorities for taking the image further. Firstly I think it is a bit colour cold, so a bit on the blue side. I think the reds might need a slight lift.

Then the background sky is rather 'busy.' A large dither - 12 pixels or so - between subs will greatly reduce colour mottle in DSLR images. Using normal noise reduction which uses pixel-to-pixel communication will probably introduce the 'oily' look which is unattractive. Dither is the best way with DSLRs.

Rob Gendler's image is a benchmark but note the exposure time and the apertures used - and bear in mind that his processing expertise is at the top end of world class.

Olly

I've had another attempt at processing this one thinking specifically about your comments @ollypenrice, and I'd be very grateful if you would take a look and tell me if you think it's an improvement.  The biggest change I made was in the stacking.  I used the Bayer Drizzle algorithm in DSS this time instead of my normal choice of AHD interpolation.  I think it has made a difference to the mottling in the background.

The other thing I've done is to create a false luminance image from my OSC following Steve Richards' guide in 'Dark Art or Magic Bullet', sharpen it quite aggressively and then add it as a luminance blend layer over the RGB image with 50% opacity.  I think it's a bit better, but feedback from experienced eyes would be very much appreciated.

 

[ollypenrice]

Dither has two purposes. It stirs around the noise artefacts inherent to the chip so that they average out. I don't think you can 'over dither' in this regard. It can also support drizzle stacking in search of higher resolution. I won't pretend to understand or use this in deep sky imaging but it's an easy Google (Drizzle stacking) if you're up for it. Here I think a controlled level of dither may be important.

Olly

[GraemeH]

Another reprocessing attempt.  Think I'm beginning to understand how layer masking works in Photoshop.

[tooth_dr]

Good job! Colours looks spot on in the latest version 

[ollypenrice]

You're really getting there.

Olly

[wimvb]

On 2018-03-22 at 21:13, tooth_dr said:

Well done Olly!

Can I ask this - can you over-dither? Yes you will lose some of your imaging field but can it be detrimental in other ways if you dither say 20px? Also would you suggest random or spiral dithering?

20 px on a multimegapixel camera hardly gives a loss in fov. Random or spiral doesn't matter either. As long as you break up any pattern from the sensor, you're ok. Dithering also helps to get rid of "walking noise", streaks that are sometimes left in the background after calibration and stacking.

[tooth_dr]

41 minutes ago, wimvb said:

20 px on a multimegapixel camera hardly gives a loss in fov. Random or spiral doesn't matter either. As long as you break up any pattern from the sensor, you're ok. Dithering also helps to get rid of "walking noise", streaks that are sometimes left in the background after calibration and stacking.

Dithering is so beneficial, I wouldn’t even bother imaging without it anymore.  When I look back at all my images from the past they all have walking noise, since dithering this is a thing of the past