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M67 - Third restack, think I've sussed it


jgs001

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After giving up trying to get more data on the Leo triplet, it was too windy for the needed sub length, I settled on going for M67 instead.

m67.jpg

I'm not that happy with how this has come out. I don't know why, but it came out of DSS green and I seem to have misplaced all the star colours... I'm going to restack and see if I can resolve the issues, I think it may have something to do with the Bias frames, I've posted about this in another thread.

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I've restacked this, and carried out approximately the same processing, but excluded the Bias frames form the stack. I didn't take flat darks, so it's probably not quite as it could be. The main difference in processing is I didn't have to pull the green channel downward. What do you think ?

m67restack.jpg

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Thanks Peter. I've found out what's causing it, but no clue what to do about it. It's caused by setting the black point to 0, which is a RAW setting in DSS that is needed when using bias frames...

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Thanks Jamie. Thanks Martin, I do prefer the background in the first one, but I just feel it's too green and pulling the colour back to normal by pulling down the green mucks up the colours.

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not sure I understand your green background problem. How are you processing it? If in PS use curves and the G channel to reduce the value but only at a low level near to the background. Anchor the curve above the mid point (approx) and drop it at around level 20-30. This should not affect star colour.

Dennis

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Dennis, it's not a green background. The entire image has a green cast to it, stars, the galaxies in my triplet image and the background. The only way to not get the green cast is to not set the "set black point to 0" option in DSS.

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John,

I had a quick play with the original and channel mixer can sort the cast out...

Set output channel to red and increase the "green" value to around 25% then use levels on the red and green channels to sort out the background.

When you stack in DSS are you boosting the saturation before saing the image with the changes applied or are you working on the autosaves...?

Peter...

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Peter, Thanks for that, I'll have a look into the adjustments. I've been adjusting in DSS and boosting saturation before saving and working on that image. I've been finding I get more consistent results that way. I'm going to restack and save the file without changes and have a play with that one also.

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Ok, I think I have this sussed now... It was a combination of setting the black point to 0 and letting DSS auto set the white balance... The green is now gone. What I do need to do is work out how to do a custom white balance shot at night...

m67unadj.jpg

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I thought that might be the case Peter. I'm hoping that it'll save me having to process out the colour cast of the LP filter, one less processing step for me seems to me to be a good call. It's not my strong point.

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well thinking about it a bit more... probably not...

As the LP level is going to be dependent on the depth of the atmosphere between the camera and the target...

You can use it as a guide to removing any colour cast introduced by the filters though which is a good place to start.... that image could be taken in daylight. in exactly the same way as you would a normal WB image...

Peter....

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Thanks for confirming Peter. I've set the custom WB up for the LP filter now. I'm just restacking all my images that went green and seeing how they come out... So that's the Leo Triplet and Bodes and the Cigar..

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DSS can take the camera white balance setting and use that, So as long as I set one, and remember to assign it before capturing the data, it should be ok. I think I'm going to need to draw up a cheat sheet to remember all the settings I need to make.

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The WB the camera uses is tagged into the RAW but not locked, so you can choose to ignore it completely. When I shoot clouds in the evening, I set the WB to cloudy on the camera as it captures the colours better. I could just adjust them in processing to get the same settings, but as it's only a button press, it's much easier.

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