What can i do. - Moon - filters????

[NewToStars (Jase)]

Was looking at the moon last night in my 8" dob.... but damn it was bright. i had to put sunglasses on or i'm sure i'd be blind by now.

i don't view the moon often, but thought i'd give it a go as i haven't done so in my new scope.

is there anything i can get to drop the bright intensity down.. it is just rediculously bright.

thanks

[vindictive666 (John)]

Originally Posted by NewToStars

Was looking at the moon last night in my 8" dob.... but damn it was bright. i had to put sunglasses on or i'm sure i'd be blind by now.

i don't view the moon often, but thought i'd give it a go as i haven't done so in my new scope.

is there anything i can get to drop the bright intensity down.. it is just rediculously bright.

thanks

yep you can buy some moon filters they sell them for the 2 inch and the smaller size ep's

[rmcpb (Rob)]

I look at the moon very often and use a variable polarising filter, available from all suppliers, as it gives me the ability to set the birghtness to a level that suits me.

Cheers

[acropolite (Phil)]

I have a moon filter and still find it too bright, Rob's suggestion of a polarising filter sounds the go. I have also used my DGM optics NPB filter, normally used to bring out the detail on Nebulas and it imparts a nice soft orange colour, removing the glow and leaving the detail.

[neB]

You can block off some of your aperture too.

Stick a piece of card with appropriately (offset for reflector) hole in it over the end of your scope.

I was mooning last night also, with a moon fliter and I was still snow-blind at the end of it (in one eye). Think I'll be trying the cover-up method next time. My scope cover has an insert built into it, so I might try that first.

Good luck.

[janoskiss (Steve H)]

Don't worry about going blind. The Moon is no brighter at night than during the day. If you observed it in daylight you would not think it was blinding. It is just the contrast between the night sky and the Moon that gets you.

Filters are better than aperture masks. The latter robs your scope of resolution so you will not be able to see fine detail that you could without it. Neutral density filters are good and inexpensive (they come in several different shades), or crossed polarisers that Rob suggested.

[rmcpb (Rob)]

Steve is right, if you want the best resolution possible then you need the maximum aperture. There is actually an astro law about this but I cannot remember the formula or the name of the law but basically the larger the aperture the finer the resolution. Masks are handy to ensure you have a fine focus but not for observing.

[robagar]

angular resolution of a lens or mirror is given by

theta = 1.22 * lambda / D

where theta = angular resolution, lambda = wavelength of light, D = aperture

[robagar]

(this basically gives you the angular size of the central disk of a the diffraction pattern of a star I think)

[OneOfOne (Trevor)]

I second the variable polarizer, I have one and it works well. A single Moon filter is only good until around a quarter moon, then you need something more.

As Janoskiss says the Moon is only as bright as during the day, it's the contrast that blows your mind. It's like looking at car headlights during the day versus at night.

[rmcpb (Rob)]

A hint, if you only have a basic moon filter and its still too bright then put a red filter on as well and things will be better, but still not as good as a variable polarising filter. Otherwise, up the magnification and you will notice the brightness to reduce.

[astro_nutt]

I use a #80A blue filter at the moment but I might get a variable polarizer now!!..thanks rob!

[neB]

Dang. I read the aperture reduction thing in an Astro book a while ago. Lies, all lies.

[janoskiss (Steve H)]

the aperture reduction (masking) does work, and for low powers it works just as well as a filter.