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Old 11-09-2013, 09:38 PM
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Is using a light pollution filter with RGB filters a bad idea.

Hi guys,

I'm thinking of adding my cls lip to my flattener whilst imaging my RGB frames. Do you think this would work ok? I live 7ks from cbd so my light pollution is horrendous and I get really severe gradients in my images.

I really don't want to experiment as it means ill have to take and calibrate/combine all my flats again.

Thanks
Sandy
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Old 12-09-2013, 05:21 AM
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Hi Sandy,

I just did a recent thread comparing the Hutech to the CLS filters that you might want to review.

However, in a nutshell, I found that the CLS does an excellent job but at the cost of around 30% more exposure necessary compared to the Hutech IDAS. The Hutech filter increased exposure to nearly double compared to using no filter at all, and the CLS about 2.4X.

In recent correspondence with Astronomik I was told that they do not recommend that the CLS filter be used in front of RGB filters, but they do recommend it be used in place of luminance. With your heavy LP it sounds like you still need some sort of help in RGB. You may want to invest in the Hutech IDAS filter. I have used it in the way you want to (in front of all 4 filters) and I have pretty good results. But, keep in mind that I've only been imaging for a bit over a year. The Hutech does increase exposure time, but not as drastically as the CLS.

Peter
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Old 12-09-2013, 06:12 AM
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I've just about given up doing any color from the big smoke. Stick to narrow band, Ha being the easiest.
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Old 12-09-2013, 07:34 AM
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Thanks Peter.
I already have the CLS CCD filter and have used it as my Lum. I works pretty well but my RGB's are that bad that when try to a dynamic background extraction on them in pixinsight, no matter what tolerance I use it only adds very few reference points and I'm unable to extract the gradients from the image.

Marc, I'm beginning to think along those lines as well.

Maybe I'll give it a shot and see what the out come is. I guess I have nothing to loose at this stage.

Thanks guys.
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Old 12-09-2013, 07:50 AM
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Quote:
Originally Posted by White Rabbit View Post

Marc, I'm beginning to think along those lines as well.

Maybe I'll give it a shot and see what the out come is. I guess I have nothing to loose at this stage.

Thanks guys.
Pros: it teaches you good calibration, flat fielding in particular and processing techniques to remove color casts and gradients.

Cons: you never get the proper colors. Shots are noisy due to sky glow and color cast changes with altitude and where you're pointing in the sky.

In the end all the color shots I got were crap when I compared them to single subs under dark skies so I figured the end result was really not worth the effort.

I originally spent a bit of money in LP filters, UHC-S, Nebulosity/Contrast enhancers and what not. They're all collecting dust now.
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Old 12-09-2013, 07:52 AM
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I found this thread on a uk forum, this guys seem to get pretty decent results imaging RGB with a CLS CCD filter in the mix.

http://stargazerslounge.com/topic/18...-final-image/#

That's it, I'm giving it a go....

Stand by, all though you may be standing by for a while it looks as though the weather is about to roll in, bboooooo.
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Old 12-09-2013, 07:57 AM
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Quote:
Originally Posted by White Rabbit View Post
I found this thread on a uk forum, this guys seem to get pretty decent results imaging RGB with a CLS CCD filter in the mix.

http://stargazerslounge.com/topic/18...-final-image/#

That's it, I'm giving it a go....

Stand by, all though you may be standing by for a while it looks as though the weather is about to roll in, bboooooo.
Keep in mind that's a galaxy picture with a black background shot at the zenith from his location.
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Old 12-09-2013, 08:08 AM
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Looks like we were posting at the same time.

Good points about the black back ground, I'll give it a crack anyway just satisfy my own curiosity. At least it might be a viable approach for certain targets, and at this stage my standards are probably quite a bit lower than yours

Thanks
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Old 12-09-2013, 08:15 AM
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I don't think it is a waste of time doing RGB in moderate LP. I have had decent results using the Hutech IDAS. The colour has worked well and has not been difficult to balance. I don't believe that will be the case with the Astronomik CLS due to the extreme blocking. If you compare the transmission spectra of the two filters they are quite different; the Hutech passes energy in each channel...the CLS does not.

However, that M51 image is quite nice, so obviously colour calibration is possible. Did you notice the length of the R subs? Your guiding will need to be super!

Peter
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Old 12-09-2013, 05:21 PM
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Hi Peter.

The guy on the the web sit I linked to was using a a CLS CCD filter with RGB filters and they looked pretty good.

If I get a break in the clouds tonight ill fire off a few frames and see how I go.

Cheers.
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