Widefield Imaage Processing Tips Needed?

[Robert_T]

Hi All,

After giving my new Canon 100mm F2.8 lens a run of imaging the other night, it became clear that for widefield images of dense star-fields that I need to use other techniques to post-process that with my prime focus shots.

With prime focus stars are usually well discriminated and objects are general easily separated. With this wide-field of Sagitarius it's more like a solid pixelated ocean of gold with darker intrusions... the stars all meld into one. The attached is from 5 x 200s at F3.2.

Do other's process widefields differently to prime focus? Any tips on processing these in images plus?

cheers,

Rob

[iceman (Mike)]

I guess the first thing is composition - the composition of your shot is not quite right. There's no real focal point. M8/M20 are good but they're off to the side. The star-field itself can be a target, but the focal length isn't quite right for that as a target on its own here. It would need to be shorter or longer.

The colour doesn't look right on this one - too yellow/green?

There is definitely a different technique and emphasis needed for widefield versus longer focal length imaging. Rich starfields don't hold up well to a lot of processing without making them hard or sharp, so lots of data and good composition are the main aspects.

[dannat (Daniel)]

Send Rob_K a message ,his results are great -only adviceisuse DSS for porcesssing. the colrs don't look right though - what wre the original subs like?

[Robert_T]

Originally Posted by iceman

I guess the first thing is composition - the composition of your shot is not quite right. There's no real focal point. M8/M20 are good but they're off to the side. The star-field itself can be a target, but the focal length isn't quite right for that as a target on its own here. It would need to be shorter or longer.

The colour doesn't look right on this one - too yellow/green?

There is definitely a different technique and emphasis needed for widefield versus longer focal length imaging. Rich starfields don't hold up well to a lot of processing without making them hard or sharp, so lots of data and good composition are the main aspects.

Thanks Mike great advice, especially the last part about the need for lots of data and less processing

[[1ponders] (Paul)]

Yep what Mike said Rob. Processing DSO whether widefield or longer FL really is very different to planetary. If you feel like spending a bit more money I can put you onto a very good book.

[Robert_T]

As for colour, don't pay too much attention with that in my original post, I was more concerned with processing for detail and was just playing with colour and came up with that below. I had another play and came up with something more different below. The subs are too light-fogged (near full moon and LP) to show much by way of colouration.

[Robert_T]

Originally Posted by [1ponders]

Yep what Mike said Rob. Processing DSO whether widefield or longer FL really is very different to planetary. If you feel like spending a bit more money I can put you onto a very good book.

<My wallet has crammed itself into my back pocket and is cowering in fear ... do tell me more

[RB (Andrew)]

Rob I can't offer any tips using IP because I only use it to register my RAWs.
I've done a quick PS adjustment to show you what can be done in PS.

Your colours just needed adjustments and the histogram was clipped.

In PS:

Open your image and go to Curves:
- with the white eyedropper choose a star that you think should be white and click on it.
- with the black eyedropper choose a section of the sky which should be black and click on it.
- with the grey eyedropper try and estimate a section where you think a neutral grey should exist (at around 18% grey) and click on that.

Now go into Hue/Saturation adjustment and do the following:

RED:
Hue = +1
Sat = +25
Lightness = +15

Yellow:
Hue = -8
Sat = +20

Cyan:
Hue = +100

Magenta:
Hue = +30
Sat = +10

You'll notice that some stars have a nice white others have a nice yellow/golden hue.
In the end it comes down to personal preference, how it looks on your monitor and lots of practice.

[[1ponders] (Paul)]

I've looked at a few books on photoshop and bought a few books on photoshop and even did two photoshop courses and while they all helped somewhat Photoshop Astronomy left them all for dead for a rank beginner like me. For me it was the ultimate cookbook.

http://www.willbell.com/ccd/photoshop_astronomy.htm

Bintel carry it as well I believe.

[Robert_T]

Originally Posted by RB

Rob I can't offer any tips using IP because I only use it to register my RAWs.
I've done a quick PS adjustment to show you what can be done in PS.

Your colours just needed adjustments and the histogram was clipped.

In PS:

Open your image and go to Curves:
- with the white eyedropper choose a star that you think should be white and click on it.
- with the black eyedropper choose a section of the sky which should be black and click on it.
- with the grey eyedropper try and estimate a section where you think a neutral grey should exist (at around 18% grey) and click on that.

Now go into Hue/Saturation adjustment and do the following:

RED:
Hue = +1
Sat = +25
Lightness = +15

Yellow:
Hue = -8
Sat = +20

Cyan:
Hue = +100

Magenta:
Hue = +30
Sat = +10

You'll notice that some stars have a nice white others have a nice yellow/golden hue.
In the end it comes down to personal preference, how it looks on your monitor and lots of practice.

Thanks Andrew, you always come up with the goods This does look more natural

[RB (Andrew)]

Yeah sorry guys, you all posted while I was composing my reply and then I got called away.

By all means check out the books available on PS for astro imaging and also maybe checkout PS books on normal terrestrial editing too.

You get good colour processing practice when you do terrestrial image editing, although astro is somewhat more challenging.

Try the eyedropper technique which is very basic but does a better job that PS's auto colour/levels/brightness - I never use these options.

Also make sure you calibrate your monitor, at the very least by using Adobe Gamma but far better by using a calibration tool like the Spyder2/3 or Huey.

I know.....more money

[Robert_T]

Originally Posted by RB

Also make sure you calibrate your monitor, at the very least by using Adobe Gamma but far better by using a calibration tool like the Spyder2/3 or Huey.

I didn't even know such a thing was possible? Can you calibrate a notebook PC screen (mine is shiny)?

[RB (Andrew)]

Originally Posted by Robert_T

I didn't even know such a thing was possible? Can you calibrate a notebook PC screen (mine is shiny)?

You can use a colourimeter to adjust your screens profile for colour accuracy.
Apparently monitor colour 'shifts' over time and regular calibration is recommended.

Here's a couple of links:
Pantone Huey
Spyder Pro