Homemade moon filter?
Posted 24 June 2013 - 11:32 PM
Posted 25 June 2013 - 10:53 AM
Posted 25 June 2013 - 11:02 AM
The Moon is *blinding* through a telescope and even a 13% filter will still result in some degree of "retina burn" after an extended moon viewing session. You would do better by cutting out some plastic polarized sunglasses. Cut two lenses and by rotating one over the other various degrees of filtration are obtained. I made a Sun filter like that only i used *three* lenses.
Posted 25 June 2013 - 01:12 PM
This is wrong; the moon is only uncomfortably bright when viewed at night because it is seen against a dark setting. You can view the moon in full daylight but it's obvious the lunar surface is only a little brighter than the daytime sky ... it won't blind you or burn your retina any more than sunlit rocks on the earth's surface will, but the bits of the moon that are projected into the eye will totally destroy dark adaptation, which will recover to its normal value over half an hour or so.
The Moon is *blinding* through a telescope and even a 13% filter will still result in some degree of "retina burn" after an extended moon viewing session.
Because magnification spreads out the light over a wider area, the surface brightness of the moon when seen in a scope is never any brighter than it is when seen with the naked eye; it's just bigger. In fact, since magnifications higher than those needed to contain the exit pupil are usually used, the surface brightness is significantly lower when seen through a scope, even if the transmission of the scope is "perfect" (which it won't be even without a filter fitted).
In my experience a moon filter with a transmission in the 13% range is far, far better than none at all (when observing against a dark sky - and for comfort rather than safety) but I do prefer something a bit denser ... I really don't like variable polarisers because of the number of surfaces and the "optical grid" inherent in the polariser scatters more light than either dye-in-glass or dichroic filters. My favourite filter for observing the moon at night is the Baader Solar Continuum filter but, if you want to preserve your night vision as much as possible, you might try a very deep red like the Wratten 29.
Posted 25 June 2013 - 03:01 PM
Posted 25 June 2013 - 06:36 PM
They do warn not to use as "sunglasses" on the package of those theater glasses.
Providing you do NOT look at the Sun with this or any type of home made filter*,I see no harm in trying this on the Moon...
* Unless the proper materiel is used...
Posted 25 June 2013 - 10:07 PM
Posted 25 June 2013 - 11:41 PM
Posted 25 June 2013 - 11:43 PM
I was perhaps guilty of hyperbolizing in my former post. What I mean by a "retina burn" is simply an overstimulated retina. If you observe the Moon for a period of time with filtration then look away at an orange mercuric streetlight you will notice that it has reddened significantly because the receptors that gather the shorter wavelengths are overstimulated and not working well.