12 replies to this topic

[AstronomyFred]

Hi all,

 

On the 12th there was a short period of clear skies and I took the opportunity to take an image of NGC 7789.

This star cluster has a good variety of star colours, so I decided to take exposures of 30 sec each, 134 in total.

 

Scope was a 102mm F7 meade apo on a HEQ5 Pro, guided with ETX70+ASI 120mm. 

Captured with APT, processed with APP and Photoshop.

 

One thing I am not happy with is the blue colour absence, I wanted to bring out the contrast of Blue and Red, but no such luck.

Any tips on that??

 

I used APP to do the stretching with DDP and keep as much saturation. 

Stretching in Photoshop did not work better, rather worse. I have read several threads, but they all end up with Acrsinh stretching in PI, and unfortunately I do not own PI... 

 

Edit: the thumbnail does show less colour than my full size result... Larger size on flickr.com/astronomyphoto

Attached Thumbnails

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Edited by AstronomyFred, 16 January 2021 - 07:00 AM.

[hobbyknipser]

Hi, Fredrick,

 

which Camera do you use and did you use a filter here?

Blue is the weakest color in RGB. Do you have a strong lightpollution at your site (which blocks the color blue most)?

I had the same problem as you at M38. Here is my thread in german: maybe, this can help you...

http://www.astrotref...104&whichpage=1

 

or here the same problem in the austrian forum:

https://astronomiefo...hp?f=36&t=16641

 

cheers

Andreas

Edited by hobbyknipser, 16 January 2021 - 09:43 AM.

[c2m2t]

Hi Fred!

To give me a frame of reference, I reviewed a number of images available on the internet and I have to say that I like your image the best. This is an extremely delicate cluster...a "puff of baby's breath" and is very difficult to capture honestly. I saw other images with bloated stars that helped to define the cluster boundary but it did not look very natural at all. Part of the issue for such a wide field shot for this cluster is that the field has no stars that are significantly brighter than others so there is nothing to draw your attention away from this delicate cluster. The star field appears so evenly dense. I saw one image taken with a reflector that showed subtle spikes on the brighter stars and this helped to increase the notion or sensation of blue. If you have an achromatic scope, it might be an interesting experiment to take the same image with it...it may just produce that bit of tiny fringing that will raise the blue signal. 

 

In my opinion, your first attempt is a very beautiful image of what this cluster really is. Creating drama that is not there, in my honest opinion, is a mistake. You created an excellent image...at least to my eye!!

 

Cheers, Chris.

[AstronomyFred]

Dear Andreas and Chris,

 

Thank you for your replies.

 

@ Andreas, I used a Canon EOS 7D MK II, unmodified and no filters.

Light pollution is not that strong and the object was near zenith.

 

Thanks for the links, I will read them and try to use tips on my processing (not my strong point).

 

@ Chris, Thanks for your kind words. I like your expression "puff of baby's breath", this is one of the reasons I liked the object. It is also less often photographed than other objects.

I try to process the images as natural as can be, appreciate you like it. 

The spikes... This is really funny you mention this. When I bought my refractor, proud as can be I showed it to my wife and the only thing she asked was "Can you now make pictures with spikes?" 

The fringing Idea is good. I tried to take all the fringing away with PS, but perhaps should have kept it.....

 

Clear Skies,

 

Fred

[chrysalis]

GREAT image!!

 

Always a joy visually when accessible.

[Tfer]

In Lightroom, use the ‘Vibrance’ controls.  It helps to recover the various colours. 
 

The stars in this shot were all essentially white until I hit the Vibrance - nothing like what was actually visible.  The Pleiades (at the top) were especially disappointing.

 

 

Attached Thumbnails

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Edited by Tfer, 16 January 2021 - 11:46 PM.

[chanrobi]

In Lightroom, use the ‘Vibrance’ controls.  It helps to recover the various colours. 
 

The stars in this shot were all essentially white until I hit the Vibrance - nothing like what was actually visible.  The Pleiades (at the top) were especially disappointing.

Can you link full res please.

 

Hi all,

 

On the 12th there was a short period of clear skies and I took the opportunity to take an image of NGC 7789.

This star cluster has a good variety of star colours, so I decided to take exposures of 30 sec each, 134 in total.

 

Scope was a 102mm F7 meade apo on a HEQ5 Pro, guided with ETX70+ASI 120mm. 

Captured with APT, processed with APP and Photoshop.

 

One thing I am not happy with is the blue colour absence, I wanted to bring out the contrast of Blue and Red, but no such luck.

Any tips on that??

 

I used APP to do the stretching with DDP and keep as much saturation. 

Stretching in Photoshop did not work better, rather worse. I have read several threads, but they all end up with Acrsinh stretching in PI, and unfortunately I do not own PI... 

 

Edit: the thumbnail does show less colour than my full size result... Larger size on flickr.com/astronomyphoto

https://stargazerslo...olour-in-stars/
 

[Tfer]

Can you link full res please.

 

https://stargazerslo...olour-in-stars/
 

Full Rez is on my computer...

 

It’s a 7.6MB JPEG.  This is as big as I can upload:

Attached Thumbnails

• 

[Tfer]

The compression algorithm is wiping out some of the colours. On my computer, the Pleiades are almost royal blue with Aldebaran and Betelgeuse a pale orange. 

Edited by Tfer, 17 January 2021 - 02:44 AM.

[AstronomyFred]

Thanks everyone for all your contributions.

 

I have read the threads sent with great interest.

 

First of all, I took 30 sec subs with ISO 400, so the raw data will not be filled with saturated stars already (this was the aim of taking 30 sec subs).

So that part of the discussions I could confirm to have followed.

 

Further to the image processing, one day I will own PI, but not today.

The idea behind most processing step seem to be one of the following:

 

1) Stretch in such a way that colours are preserved, mostly by increasing saturation prior to stretching. 

 

2) Take a stretched image and make a star mask to *gently* feather your way down to the center of stars. 

 

I tried to combine both methods a bit. 

 

My issue is that when making the star masks I loose resolution bit by bit. I am also not sure which overlay function to use with Photoshop layers. Lighten seems to do nothing, so I went with luminosity. Not sure if that was the best way.

 

I add below as short animation. 

Three frames with 2 seconds each.

Order of animation is:

- Original Edit

- New Edit

- Stack stretched only once with levels adjusted.

 

 

 

I think the star masks are the best methods, but which overlay to choose and how to deal with the reduced sharpness?

I have tried adding a L channel to RGB, but without a good result..

 

Tips welcome..

[c2m2t]

Hi Fred!

I am looking forward to a side by side comparison when you have maxed out your second processing regimen!! 

 

Cheers, Chris.

[DantheSpaceMan]

What was your white balance on the camera? And did you use Camera as shot or Adobe Daylight for raw converter? 

 

If you'd like, you can link the stacked image to dropbox (PM if needed) and I can stretch with rnc-color-stretch to see if any of the blue's come out. Just an experiment. You'd have to read up on Roger Clark's process and philosophy if you like the result and want to retain it. Or, if it doesn't come out to your liking, at least you know.

 

In any event, have you tried using RawTherapee for the RAW image converter, as opposed to photoshop? Star structure and color of course subjective can come out better using this program rather than PS. 

[AstronomyFred]

sorry for the delayed response... I sometimes have to pretend I am working... 

 

What was your white balance on the camera? And did you use Camera as shot or Adobe Daylight for raw converter? 

 

If you'd like, you can link the stacked image to dropbox (PM if needed) and I can stretch with rnc-color-stretch to see if any of the blue's come out. Just an experiment. You'd have to read up on Roger Clark's process and philosophy if you like the result and want to retain it. Or, if it doesn't come out to your liking, at least you know.

 

In any event, have you tried using RawTherapee for the RAW image converter, as opposed to photoshop? Star structure and color of course subjective can come out better using this program rather than PS. 

The white balance was on Auto, but the Raw images were processed without the white balance settings during calibration and stacking.

I loaded the raw images into the stacking software (APP).

 

I did look at Rawtherapee (I actually used to be a Nebulosity user since Version 2, so am familiar with clarkvision, very informative and good site), but it seems very elaborate to me and would not fit into the workflow that I have now. Do you use Rawtherapee? I do use the align each channel separately in APP.

 

Not so sure the loss of colour is in capturing + stacking of the image, as the stacked image mildly stacked has a ton of colour.

 

Thank you for the offer, very kind of you!

But unfortunately I don't have a dropbox account (shame on me  ) ...

 

How do you do the rnc colour stretch?