Moon Filters

[stuffandthat (Ash)]

Hi guys, I like looking at the moon and was wondering if it was beneficial to get some moon filters? I was looking at the Bintel 1.25" ND96 moon filters but not sure what percentage of transmission to get. Are these filters any good, or is it better to spend a bit extra and get something else?

[gaseous (Patrick)]

You can get adjustable polarizing filters on Ebay for very little money - great for adjusting the amount of brightness you want.

[stuffandthat (Ash)]

That's a good idea. They seem to be about the same price as single filter too.

[Stefan Buda]

If the Moon is too bright for you, it only means that you are not using enough magnification. One should never waste photons, unless observing the sun.

[Wavytone]

As per Stefan - max the magnification. Even in my 10" its not too bright, then.

[mental4astro (Alexander)]

Yes, I agree with the notion that it depends on the magnification being used.

For low magnification I use a pair of polarizing filters. By twisting one against the other it is possible to regulate the amount of light. This the only way I am able to sketch the full Moon with an 8" scope.

Now when exploring the terminator, you are using high magnification, and then no filter is necessary. I never use a filter when pushing 200X and over.

Don't forget, when you are looking at the Moon, forget dark adaptation! There is nothing subtle about the Moon. Your eyes will be stunned like coming inside from a sunny day. You DON'T need a feeble red light. On the contrary, just use whatever white light you have, as this will actually make things safer and easier for you. When sketching the Moon, I leave the porch light on and I use a bright white headlight to illuminate my paper - your eye is stunned looking at the brilliant Moon, so it is just dumb trying to use a dim red light to shine your paper... or your way around if you are not sketching.

[Wavytone]

Optimum resolution for the Mk 1 eyeball occurs around 0.7-1.5mm aperture. Go figure.

[stuffandthat (Ash)]

I'm using an 8" Dob and usually use a 30mm 2" 68deg eyepiece or a 15mm 1.25" Plossl. I was looking at using the filter to make the view a little darker to see more of the moons character.

[mental4astro (Alexander)]

Ash,

I would suggest you go through this thread I started that deals with observing the Moon and planets:

Observing the Moon and planets - the good juice and cheats

It discusses not just things to explore on the Moon and planets, but also talks about getting the most out of your scope with understanding its limitations along with tips and tricks.

Also discussed are filters for the Moon and planets.

If you only have 30mm and 15mm eyepieces, I would also suggest you invest in a shorter focal length eyepiece right now than a filter. An 8" dob is a marvelous scope that will give you many years of good service. A 5mm or 6mm eyepiece will give you not only higher magnification, but will also be less brilliant on your eye. Look for an EP with at least a 58° apparent field of view, as this will give you a longer drift time than a plossl eyepiece for the same focal length.

If you would like a couple of eyepiece recommendations, just let me know as at this point in your thread it is beyond the scope of the thread. And you don't need to burn the Big Bucks to get a very good short focal length eyepiece.

[stuffandthat (Ash)]

I will give your guide a read!

I do have some other eyepieces. It's been a while since I've had the scope out so I can't remember what the other are!
Some eyepiece recommendations would be greatly appreciated.

[va1erian]

Originally Posted by gaseous

You can get adjustable polarizing filters on Ebay for very little money - great for adjusting the amount of brightness you want.

When I was using the Celestron 90GT WiFi Cosmos refractor, I found Moon was too bright for my eyes (at whatever magnification). I acquired a pair of polarisers, and I discovered that I did not like the decrease in resolution which they introduced (the image became a bit fuzzy).

Then I bought the cheap neutral density filters, maybe even from Bintel, and the image quality was fine. I think I got the 50% and 13% transmission, thus I was able to set 6.5% transmission, too, by combining the filters.

I was glad that I did not get the so-called "Moon" filter, as it was nothing else as the green filter, and I hate the colour tinge to the Moon image. (One could see the dark-green colour on the product picture of the filter.)

As a matter of fact, the Celestron "Moon" filter claims its transmission to be 13".