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opinion welcome on light pollution filter


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Hi,

I have been seeing a lot of topics related to light pollution filter and of course opinions are very broad.

To explain my situation: I live in a small town (20 000 habitants), in the outer edge, direction south which is very clean sky (I would say typically a visual limiting magnitude of 4,5 to 5 over 200 degrees angle direction south, above 15 degrees. Looking north, it goes down to maybe 3,0 to 4 over 150 degrees wide to 60-70 degrees up. So I would say pretty clean overall for being still in a (small) town. Few street lights around (I am checking what type) but never direct (my garden is a bit like a "hole", below street level so no direct light coming really.

Now my scope is a C8, unguidded and unmodded canon EOS1100d. I also have the FR 6.3 celestron. I manage 60-90 sec at f10 and 90-120 sec at f6.3 unguidded with good round stars which is fine to me (I am not after investing in a guide today). I use ISO1600 at f10 for those 60-90 sec without much problem, but with the FR 6.3, but I basically need to go down to ISO800 and even at this ISO, above >60 sec I start to be on the edge of histogram shifting too much (especially looking north).

In principle, I am after taking the benefit of longest sub possible unguidded, to reduce work out when processing the subs. With shorter sub of 20-45 sec, I manage well in post processing with levels, curves to go around the problem and keep good contrast, but as I am after 1-2 hours total exposure for deep sky, I am not after playing with several 100´s sub of 20-30 sec while I can manage 60-120 sec unguided (meaning maybe 60-80 subs at max to work with)

I am not for visual imprement.

I hope that gives a good idea of my situation and I would like to know what could be a right light pollution fiter in my conditions and also if this would work fine, if I would really benefit of it or that won´t bring much.

thanks in advance

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Hi,

I have been seeing a lot of topics related to light pollution filter and of course opinions are very broad.

To explain my situation: I live in a small town (20 000 habitants), in the outer edge, direction south which is very clean sky (I would say typically a visual limiting magnitude of 4,5 to 5 over 200 degrees angle direction south, above 15 degrees. Looking north, it goes down to maybe 3,0 to 4 over 150 degrees wide to 60-70 degrees up. So I would say pretty clean overall for being still in a (small) town. Few street lights around (I am checking what type) but never direct (my garden is a bit like a "hole", below street level so no direct light coming really.

Now my scope is a C8, unguidded and unmodded canon EOS1100d. I also have the FR 6.3 celestron. I manage 60-90 sec at f10 and 90-120 sec at f6.3 unguidded with good round stars which is fine to me (I am not after investing in a guide today). I use ISO1600 at f10 for those 60-90 sec without much problem, but with the FR 6.3, but I basically need to go down to ISO800 and even at this ISO, above >60 sec I start to be on the edge of histogram shifting too much (especially looking north).

In principle, I am after taking the benefit of longest sub possible unguidded, to reduce work out when processing the subs. With shorter sub of 20-45 sec, I manage well in post processing with levels, curves to go around the problem and keep good contrast, but as I am after 1-2 hours total exposure for deep sky, I am not after playing with several 100´s sub of 20-30 sec while I can manage 60-120 sec unguided (meaning maybe 60-80 subs at max to work with)

I am not for visual imprement.

I hope that gives a good idea of my situation and I would like to know what could be a right light pollution fiter in my conditions and also if this would work fine, if I would really benefit of it or that won´t bring much.

thanks in advance

Hi,

The only proper way of telling, is for someone to carry out a full spectrum analysis of the ligfht from different DSOs, in particular galaxies of different types and compare the result with and without LP filters to determine if it blocks any particular wavelenght in detriment. Then we would know for sure. BTW , for a hobby based on some really hard scientific base we seem to put a lot of faith in heresay and anecdotal evidence.

A.G

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