Originally posted by Raybo Good suggestion Raybo. I use the Hutech IDAS 48 mm Light Pollution Filter almost all the time. It fits Telescope 2 inch eyepiece holders directly, but with adaptors will fit most lenses. For example I just mounted my IDAS to a DA Pentax 50-200 using 52-49 and 49-48 step down filter adaptors. The adaptors are cheap enough for me to acquire a collection so I can put filters on most all my lenses. If you go way down like my 19 mm Vivitar which is threaded for 62 mm down to a 48 mm IDAS you may get some vignetting, but I've done it.
Hints: The 48 mm adaptors are not common in camera stores, I have a Kalt 49-48 and use the 49 end to go to all other sizes. Be aware some companies are not consistent as to what direction Step Down is or which number appears first on their web sites. I've bought a couple that, "went the wrong way."
If you live in a city with visual MAG 3-4 sky like me, you gotta use an LPR filter.
Here is a dark site image with a filterless K110D and a Sigma Zoom at 210mm, I don't think I had the IDAS filter at the time. 30 seconds * 25 images. NGC 2024 & B 33 & NGC 1997 & M 42 & M 43 in Orion.