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CLS filter effect on exposure length

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#1 robininni

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Posted 19 April 2013 - 09:41 PM

When using an Astronomik CLS CCD filter (passes 95% of various important light), am I really only hurting my exposure length compared to non filter use by 5%?

Thanks,

Rob

#2 DaemonGPF

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Posted 19 April 2013 - 10:01 PM

Not really. I used one for a while. Didn't really have to compensate with exposure length changes in general, but I would mention the notable heavy loss in the blue part of the spectrum which was really apparent to me when shooting things like Trifid, or Rho Ophiuchi.

#3 JoseBorrero

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Posted 19 April 2013 - 10:35 PM

color balance will suffer!

#4 RedLionNJ

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Posted 20 April 2013 - 06:59 PM

If I was asking this question, I'd word it as "how much longer can I expose for, compared to not using a CLS filter?". This is because you want to expose for as long as possible (to build up S/N ratio) before sky fog becomes a dramatic nuisance.

You want to expose as long as you can (and tracking/guiding allows), while keeping the histogram away from both edges.

#5 Magellan

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Posted 20 April 2013 - 07:19 PM

I used to use a Clipin CLS filter. I cursed color issues, weird halos. I no longer use it, trusting my sky limited exposures more often now and getting great color!

#6 JoseBorrero

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Posted 20 April 2013 - 07:50 PM

choosing a DSLR exposure is easy. Is always said as: the peak histogram has to be 20% to the left side. You must do exposure samples using different times. This change on differents object for ex. Nebulas vs Galaxies vs Globular clusters vs Open Clusters, All can be different.

#7 budafuko

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Posted 21 April 2013 - 07:24 AM

What do you mean by 20% to the left side?

#8 DaemonGPF

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Posted 21 April 2013 - 09:59 AM

Getting the data peaks away from the left hand side of the histogram by about 20% of the total range is what he's suggesting. In other words, exposing long enough to get the data off the ground to give processing wiggle room. I usually shoot to get my spikes near the 1/3 mark on the histogram, but I think it's slightly subjective on this particular topic.

#9 budafuko

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Posted 21 April 2013 - 08:04 PM

OK, Thanks.

#10 Ranger Tim

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Posted 22 April 2013 - 06:47 PM

When shooting with a really slow scope it can lead to noticeably longer exposures, which in turn can lead to more chance for guiding problems. I really don't like to use it unless I'm back in a light polluted area like I had in Virginia. But out here in Idaho? WOOHOO!!! Darkness is a beautiful thing.

The color balance is touchier but can be alleviated by using custom white balance or PS trickery. Secondary reflections can be a problem but steps can be taken to minimize them too.

#11 JoseBorrero

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Posted 22 April 2013 - 07:10 PM


Thanks for ask. follow link here: http://www.astropix....TROP/QUICK2.HTM


What do you mean by 20% to the left side?



#12 jsines

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Posted 23 April 2013 - 12:43 PM

When using an Astronomik CLS CCD filter (passes 95% of various important light), am I really only hurting my exposure length compared to non filter use by 5%?

Thanks,

Rob


The better question is - how does the exposure length compare to not using one? I live in a white zone, Bortle scale 8-9, and I'm able to take 3 minute subs using my Astronomik clip-in filter in my Canon. My exposure time right now is limited by lack of guiding and accuracy of polar alignment. This would be impossible without it. I probably couldn't get longer than 30 seconds without any filter.

#13 Magellan

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Posted 23 April 2013 - 01:45 PM

I have a friend, in SQM 19 skies, actually get integrated flux nebula around M81 from 2 minute subs! just ALOT of them :) He was just using his 8" Newt with a 60Da






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