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Moon Filter

Started by mrvolvo, 04/08/2009 07:03PM
Posted 04/08/2009 07:03PM Opening Post
In the past I haven't spent much time observing the moon but I just started working on the AL Lunar Club List and discovered the need for a decent moon filter. I'm primarily using my little TV-76 for this purpose, mostly with 9mm and 5mm Naglers.

1. The Meade adjustable polarizer I've used with other scopes is too long and won't allow this scope to focus.

2. At a star party the other night, I borrowed someone else's "moon filter" but upon holding it up to the light, I could see that it was just cheap tinted plastic with severe ripples which distorted the view. I passed on that one.

3. I borrowed another person's "moon filter" (this one marked "Moon" on the metal cell) and it looked to be made of real glass, but when I installed it on my eyepiece, I found it had a distinct sickly green tint.

In an attempt to get my hands on a good quality neutral density "moon filter" to make viewing more comfortable, I ordered (but have yet to receive) a Lumicon 50% transmission neutral density filter, made of real optical glass with optical coatings on both sides. Am I on the right track or should I be looking for something else?
Posted 04/08/2009 09:13PM #1
I'm no expert. But, 50% light reduction seems like a bit much for a moon filter. It might be good for a full moon, but basically the filter is just to take the brightness down a notch so the moon isn't hurting your eyes. A 10% to 25% light reduction would seem better for most moon phases.

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I have several telescopes, but none are semi-APO, APO, or in anyway valuable.
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Posted 04/10/2009 06:53AM #2


In an attempt to get my hands on a good quality neutral density "moon filter" to make viewing more comfortable, I ordered (but have yet to receive) a Lumicon 50% transmission neutral density filter, made of real optical glass with optical coatings on both sides. Am I on the right track or should I be looking for something else?

Most Moon filters have traditionally been blue or green. That said, I don't care _pea turkey_ for any of 'em. I've rarely found the Moon too bright to observe comfortably, and when I do, I'll use a color filter, an 80A or similar. These will not only cut the light down, but, unlike a neutral density filter, will enhance various details. Which a polarizer can also do.

Uncle Rod

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Posted 04/10/2009 05:42PM #3
I've never found Moon filters either necessary or desirable. With some experience, you get used to the brightness level. Also, the Moon has nice black shadows and very bright white albedo features. Any type of Moon or polarizing filter seems to make the whites a bit muddy and the blacks a bit gray.

Clear skies, Alan
Posted 04/18/2009 05:51PM #4
I use a binoviewer, which cuts down brightness by a little over half due to the light split, and I use enough magnification to reduce the exit pupil to below 1mm. An exit pupil of about 0.5mm is ideal with a high quality refractor or Mak scope when binoviewing the moon. Planets need a bit larger exit pupil due to their lower brightness. If I ever use a filter, I forget about the moon filter and use a red or orange filter, or you can use a different filter in front of each EP, such as a red and blue, for a more 3D image. My preferred scope is a 150mm LOMO Mak-Cass and a mag of about 250X on a normal night with average seeing conditions. That's an exit pupil of 0.6mm and there is no need for a moon filter. The binoviewer greatly reduces floaters that are problematic with small exit pupils.