Mask for 8" refractor

I plan to make a mask for my 8" refractor so that I can comfortable observe the moon. I plan to make a 3.5" circular hole in a spare dew shield cap. Any opinions on whether the hole should be centered or off-axis?

There should be no reason for it to be off-center on a refractor. On a reflector, a mask might be off-center to avoid the secondary. A neutral-density filter might be a better solution, in that it would decrease the brightness without giving up the resolution that the full aperture provides.

Agree with the ND filter. I use a variable moon filter on my 14" and its great. I think I got it for $25 here on Astromart, they go for about $40 new.

Anthony,

I would not go less than 5" on the mask. I never use a mask or filter unless it is close to full moon. But I also usually use a binoviewer while viewing the moon, that reduces the light throughput just enough where it is not a problem.

DMC
Pittsboro, N.C.

There is really no need for a mask, which reduces resolution or filters. While the Moon may seem overly bright, it is not really all that bright and time and experience will allow your eyes to adjust.

I've tried both neutral density and polarizing filters on the Moon (with an 8" refractor). The Moon has some lovely bright, white areas, and very black shadows. Filters muddy the pure whites and turn the blacks somewhat gray.

An interesting read is "Some thoughts on the art of vision" on page xx of Harold Hill's "A Portfolio of Lunar Drawings."

Mr. Hill makes no mention of using filters, and the fine drawings of the Moon done by Alika Herring and published in Sky & Telescope from time to time long ago (in the 1950s and 60s, IIRC) make no mention of filters.

Clear skies, Alan

Thanks for the comments everyone. I purchased a neutral density filter and even when using it the moon was painfully bright. I've already obtained the extra dew shield cap so I'll ship it off to PreciseParts to have the hole made.

Tony