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Does a clip in CLS filter (canon Dslr)

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  • shropshire lad changed the title to Does a clip in CLS filter (canon Dslr)

Are you talking about one of these kinds of filters?


For emission nebulae you will still have the 2 most important wavelengths captured, OIII at 500-ish and Ha at 656nm. This means you cut light pollution quite a lot depending on what kind of lighting you have around you (with LED lighting, not as much, since they are broader spectrum white instead of the old orange-yellow lights CLS filters are meant to block).

For stellar objects, like galaxies, some reflection nebulae, dust clouds etc you will lose up to half of the incoming signal and almost all of the orange-red components in them. The resulting image tends to be very green and difficult (impossible really) to present as a real colour image. Up to you to decide whether a real colour result is what you want in the end, but if it is then i wouldn't use a filter like this. For galaxy imaging there really is no filter that cuts just light pollution and preserves the starlight signal, since they share the same spectrum. In my opinion light pollution filters have no place in galaxy imaging as i think there are more negatives than positives with the missing colours and the arguably not helpful at all LP reduction.

In both of these cases you will need to expose longer to reach the same amount of signal as an unfiltered shot since you have less signal coming in to swamp your read noise. But if you are considering a light pollution filter im going to assume you have a lot of it and in that case you probably dont have to worry about the exposure length thing too much. The more you have light pollution the shorter your subs can be. No harm in longer subs of course, but also no need to.

Here is a recent thread discussing the exposure length thing in detail (gets technical and math-y, not sure i understand half of it):

In short: Yes, you might need to expose longer.

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Personally I would say that unless imaging narrowband, try not to us LP filters unless absolutely necessary. Just get a good gradient removal tool. I image in Bortle 5 to 6 and don't use filters for anything in RGB. To be honest most of the lighting is LED so the benefit is pretty minimal anyway.

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