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Derbyshire Dave

Blue tinted images with CLS filter

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Derbyshire Dave

I live in a small village, and whilst the light pollution is nowhere near as bad as in a city, there are sodium street lights close to my house.

 

I recently bought a 2 inch Astronomix CLS filter, about £110, to try. Bad weather after I had bought it meant I didn't try to use it until a few weeks ago, and even now I have only had a few goes. Holding it up to the street lights seemed promising, as they disappeared (well not literaly :huh:)

 

The results I got back were encouraging in that they did not have nasty gradients which I had seen before, but, on the negative side, were very blue. Below is an example..

 

I have coped with this so far by going into Photoshop, choosing the levels menu, and then using the 'Dark' dropper to set the black point. This works quite well, but I do seem to lose a little detail.

 

I was just wondering whether there were other, more subtle techniques, either during the stacking stage in DeepSkyStacker, or during post processing, in Photoshop..

 

Thanks guys..

 

 

OrionSmall2.jpg

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Derbyshire Dave

Thanks Darren , will give that a look.

 

Ron, it's a DSLR camera

 

 

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Ron Clarke

I think Darren's link is worth reading Dave, I have a CLS fitted to my 1000d but not a full red filter removal?

 

Cheers

Ron

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Derbyshire Dave

Thanks Ron. Yes, have been looking at it this morning, and made some progress, on the Photoshop side. Will continue playing tomorrow and report back. My camera hasn't got the IR filter removed btw

 

Cheers

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Ron Clarke

Mine has but not the fully modded type! This is M42 with my set up.

130227M42Final2sm.jpg

Edited by Ron Clarke
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The Bagman

have the same problem but use per channel RGB calibration in Deep Sky Stacker (recommended Settings) which seems to correct the blue colouration

 

Chris

 

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Perkil8r

I used to use the eyedropper technique in Photoshop. The issue with your posted image is that there isn't much true "black" area to click on as there is nebulosity almost completely across that area. Stick with it though, it's well worth it.

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philjay

I only get that if I have taken the shot to early, not quite dark enough. The filter I find gets blue if there's too much ambient light around.

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Derbyshire Dave

Guys,

 Thanks for all the comments, I wouldn't have know where to start without your help.

 

 Took some time yesterday and today to have a bit more of a play. I realised in doing so that I have not enough blue images to make definitive judgement, so I need to take some more and come back and try these techniques again when I have some more blue shots, and I'll make sure I take them when it's more dark.

 

  Ron, the picture you took of M42, did that start from blue tinted shot(s)? It's really well balanced.

 

  I played with the Photoshop technique of looking at the histogram and looked at the 'levels' numbers for each of the three peaks. On the orion shot, could clearly see the very low level of red. I found it a bit difficult to interpret exactly which point I should be taking those numbers, but I made rough guesses, and used the colour balance too, I upped the red, and downed the blue, until all three were about the same. The result of this was a much more balanced picture, and then I used the black eyedropper, and got a much better picture than using the eyedropper alone. So something definitely to try again.

 

  Regarding the DSS background calibration, this is where I really struggled with lack of images, so must re-assess. In principle though, I tried two techniques. The first was to use the background RGB selection (second picture attached here). When I did this I found that when the finally produced TIFF file was loaded, the three colour peaks were co-incident.

  The second method was to use 'Per channel background calibration'. The final image here had divergent peaks for the three colours. I then used the sliders in DSS to slide the right peak to the right, and the bluwepeak to the left, until they were both on top of the green peak, then clicked 'Apply'.

  On the one set of images I have to play with, the second method appeared to give better results. I need to re-visit with more photos.

 

 

  

 

 

Capture.JPG

Capture2.JPG

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Perkil8r

you've reminded me, in dss I used to align the historgrams before saving the tif file for processing. It didn't lose any detail but did solve the blue hue. Even then though stars did tend to be quite blue so after all the processing I used to knock the cyan channel down in saturation quite a bit. That seemed to cure it nicely.

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Orion

Dave

 

I’ve just bought something called Photoshop Astronomy Tools Actions ($21.95).  It was recommended to me by my astro friend John Schnupp in USA.    Here’s the link, which shows you what it does.   It looks like actions which can be done using one click (I think) and it does several steps all in one go.  There is a list of illustrated examples of what it can do, and I think removing blue cast was one of them.  If it a series of steps can be done in a single click, it could be a big time saver because it would allow trying several things very fast.

 

http://www.prodigitalsoftware.com/Astronomy_Tools_For_Full_Version.html

 

Derek

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Derbyshire Dave

Derek,

   Thanks and good to hear from you. This looks really interesting doesn't it. I'm away on holiday at the moment, as soon as I'm back I'll look into this.

cheers

Dave

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Graham

A couple of questions.

Are you capturing in RAW mode.

Are you balancing the colours in DSS after stacking.

Edited by Graham

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Derbyshire Dave

Hi Derek,

  Decided to stay away another few days, so not back until Monday, when I'll get a chance to have a better look at this. You say you have bought them, have you had a chance to try them yet?

 

Hi Graham,

  Yes I am capturing in RAW, and am balancing the three colour graphs,

 

Cheers

Dave

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sdavsky
On 26/07/2017 at 10:51, Derbyshire Dave said:

Hi Derek,

  Decided to stay away another few days, so not back until Monday, when I'll get a chance to have a better look at this. You say you have bought them, have you had a chance to try them yet?

 

Hi Graham,

  Yes I am capturing in RAW, and am balancing the three colour graphs,

 

Cheers

Dave

Hello mate.

Blimey Dave, you've come a long way in the last few months

 

cheers

Dave

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Derbyshire Dave

Thanks Dave, Let's see what happens next .. still havent really got to the bottom of processing the CLS images though

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