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I did a direct comparison tonight of the Ring Nebula. These are straight out of the camera. I using a 2.5x televue barlow, so I'm not using the coma corrector.

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I haven't done any imaging in heavily light polluted skies, so I've had no need to use filters such as these. That having been said, I've wondered to what extent light pollution effects can be mitigated in post processing.

Your comparison images here show that the filter clearly makes the image look much better as it initially comes out of the camera. The sky background is obviously better, as is the contrast.

To make a bit more level (no pun intended) of a playing field, I took each of your images and applied a levels adjustment - just setting the grey point and the black point on each of the images. Here's the levels adjusted image without the filter:



And here's the filtered version with the same levels adjustment:



To me, the filtered version looks like it definitely has less noise, although its lost a lot of the dimmer stars (not suprisingly). Because of this, it also doesn't show the central star of the ring as well as the unfiltered image.

I like the star colors in the filtered version better, but I suspect this is just because the stars are less saturated than their unfiltered counterparts.

I'm not certain which of the two images could ultimately produce the best final result when used as part of a stack of subexposures. We wouldn't normally try to make a final image from a single 2 1/2 minute sub, so I'm not sure its fair to draw much conclusion from these single subs.

I'd be very curious to see comparison images where there was an hour or so worth of subs on an object like this (one with the filter, one without). Then, if we just applied a levels only adjustment, we might be able to draw some good conclusions as to what benefits the filter may be providing towards a final, processed image.

It also be curious to see the same type of comparison on other types of DSOs - emission nebulae, galaxies, etc. I think that would be quite useful in answering the subject question (do lpr filters really help).

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I can only say that I have to use the filter from my home. Nebulae, galaxies, comets... whatever I shoot. I'm usually limited to 4 minutes on the better nights at f/4 800ISO with the CLS Filter. Without it I'm down around 1.5 minutes. The darker your sky is, the less you will need it.

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Whether you have something to complain about or not is not fully clear According to my calibration here if you get to mid histogram with 1.5 minutes at f4 and ISO 800 then you have a reasonably decent sky, Visual Limiting Mag 4.5 or thereabouts. In the summer you should be able to just make out the Milky Way in Sagittarius. I suspect that very many people here would love such a "dark" site Now, if that 1.5 minutes gets you a fully saturated sky (like for my home) then you have my sympathy...

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Scott, there is no doubt in my mind that LPR filters improve images of narrowband objects (Ha and/or OIII rich), with M57 being on of them. My point was that LPR filters do not necessarily improve images of wide-band objects like galaxies or reflection nebulae like M45 or M78.

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