Glom
15-January-2006, 03:35 PM
My society recently purchased a Meade Series 4000 Light Pollution filter. When it arrived, it was labelled as a Meade Series 4000 Nebula Filter. The invoice that came with it said it was what we ordered. I also couldn't find a Nebula Filter so labelled on the website's catalogue. Is this likely the light pollution filter by another name?
ottUp
15-January-2006, 03:46 PM
My society recently purchased a Meade Series 4000 Light Pollution filter. When it arrived, it was labelled as a Meade Series 4000 Nebula Filter. The invoice that came with it said it was what we ordered. I also couldn't find a Nebula Filter so labelled on the website's catalogue. Is this likely the light pollution filter by another name?
Yes, that's a "Light Pollution Filter". There are basically 2 kinds:
"broadband" filters work by allowing most light to pass, but blocking certain frequencies -- typically the light emitted by mercury-vapour street lights. They are only marginally effective, but work for any kind of object.
"narrowband" filters, also known as nebula filters. This is what you have. They work by blocking almost all light, but allowing through the specific frequencies that are emitted by the glowing gas in nebulae (typically the frequencies emitted by charged hydrogen and/or oxygen). These are extremely effective, but only on nebulae.
Glom
15-January-2006, 04:17 PM
Ah that's good. Thanks.
Dave Mitsky
16-January-2006, 01:07 AM
You may be interested in David Knisely's excellent comparison of LPR and nebula filters.
http://pages.sbcglobal.net/raycash/filters.htm
Dave Mitsky