The colour of my moon filter

ThunderChild (Chris) · #1 07-02-2006, 09:18 AM

Hey all,

I don't know what colour most moon filters are, but my one is green.
Seems to work Ok to my eye (ie - I don't get the glare of a million light bulbs when I look away :-), but I started wondering why the colour green was chosen.

We go to lots of effort to avoid light and use red light to preserve our night vision. Why aren't moon filters made red to keep our night vision going?

Chris

rmcpb (Rob) · #2 07-02-2006, 09:42 AM

I can't comment on the green colour, mine appears to be greyish to me but the colour does not really matter as the filter is just to reduce the amount of light getting to your eye, on a nearly full moon I combine my red filter with my moon filter to further reduce the light. The light bouncing off the moon would be most of the spectrum, its just reflected sunlight afterall so by reducing this light to a relatively narrow colour band the amount getting to your eye is reduced. It does not matter what colour that is as the levels are at the "ambient" level and not an artificial level produced by a torch or light bulb which would completely wreck your night vision.

After saying that, looking at the moon will wreck your night vision for DSOs as the light level is soooooo much higher. So a good rule of thumb is to do your lunar observing last, if possible, otherwise lunar observing, then doubles and clusters, then onto the nebulae by which time your eyes should have recovered from the bright moon

Cheers

barees63 · #3 07-02-2006, 10:32 AM

My understanding of standard Moon Filters is they are a combination of a Neutral Density filter to reduce glare with a green hue to increase contrast. The other option for a moon filter is a polarising filter which are basically an adjustable Neutral Density filter (rotating two polarising filter elements progressively reduces light transmission) .. not a bad idea since I still find the moon brighter than it needs to be be thru my ordinary Moon Filter..

toetoe (Peter) · #4 07-02-2006, 10:33 AM

Just wondering if one did use a Red type of filter for viewing the moon, would the detail be less than using a Green type or Grey for that matter. I have 2 moon filters, 1 being the green type and the other is a grey type and find very little diff between the two of them.

janoskiss (Steve H) · #5 07-02-2006, 10:51 AM

Red light has longer wavelength, so you would get less resolution; although for large-ish scopes seeing is the limiting factor more often than not. You'd get the best resolution with blue or violet light (double that of red), but our eyes (and brains) are most sensitive to green. So green is a good compromise I guess.

I use an ND (neutral density) filter combined with a blue filter (80A) on the Moon, and find it much more agreeable than the green Moon filter.

I would like to try through a polariser. It should highlight different features as you rotate the polarisation angle, depending on the angle of reflection of the sunlight. Whether it does or not depends on how specular the Moon's surface is, I guess.

Anyone notice the view change when rotating a polariser (or the eyepiece with the polariser attached)?

Now, why don't I just try with my polaroid sunnies?

ThunderChild (Chris) · #6 07-02-2006, 11:07 AM

Quote:

Originally Posted by janoskiss

I use an ND (neutral density) filter combined with a blue filter (80A) on the Moon, and find it much more agreeable than the green Moon filter.

I notice that bintel are selling those two filters (GSO 80A and GSO ND-96) for $15 each. Before I go and get anything, what are people's opinions on the essentials in filters for beginners? I don't want to buy stuff which I really do not need or will only give marginal improvements. Currently most interested in planets, moon and nebula - but that will change no doubt as I get into things more and more.

Without going overboard into expensive land, are there any basic filters which you'd recommend I get for various things which would make a big difference to what I see?

Cheers,
Chris

rmcpb (Rob) · #7 07-02-2006, 11:33 AM

Chris,

Why don't you just try one coloured filter, either red or blue, to go with your existing moon filter and just go one step at a time. I prefer the red filter when the moon is really bright as it tends to preserve some of your night vision.

Cheers

janoskiss (Steve H) · #8 07-02-2006, 11:47 AM

You won't get much out of most filters, Chris. They are of limited use even on large aperture scopes. The ND by itself should make a good Moon filter for your 6" scope, if you don't like the green colour of the standard Moon filter. Colour filters are pretty useless IMO. You will use them once or twice and that's it. A narrowband nebula filter might be of some use for cutting down light pollution around gaseous nebulae. I have the DGM NBP filter (which is said to be one of the best of its kind) you can try in your scope and see what you think.

ThunderChild (Chris) · #9 07-02-2006, 12:16 PM

Quote:

Originally Posted by janoskiss

The ND by itself should make a good Moon filter for your 6" scope, if you don't like the green colour of the standard Moon filter.

You said you like to use the ND in combo with a blue (80A). In the looking around I've done, I've read comments saying that the 80A is good for getting detail out of Saturn, Jupiter and Lunar. In fact, some comments I've read suggest that one filter as the one to get if you only get one.
Thoughts?

Quote:

Originally Posted by janoskiss

A narrowband nebula filter might be of some use for cutting down light pollution around gaseous nebulae. I have the DGM NBP filter (which is said to be one of the best of its kind) you can try in your scope and see what you think.

That would great - would love to take a sneak peak through it. If there's one which will help me get better nebulae views from my light polluted backyard (and it isn't insanely expensive), I would love one. BTW, what is a DGN NBP and how much does one cost?

From what I've heard, I'm forming the view that I'll probably look for two filters - maybe three.
My first priority is : GSO 80A (blue - $15 from bintel)
Perhaps a ND (also $15) as well (or should I swap this for the 80A?).

Finally, if that filter which will definitely assist with nebulae (DGM NBP) in my situation, that is on the list.

janoskiss (Steve H) · #10 07-02-2006, 12:32 PM

I said ND only for you because your scope is a 6", so the Moon won't be as bright as in my 8".

Edit: Another thing. As you crank up the power the image gets dimmer, so in good seeing, for looking at fine surface details at high magnification, you might not even need a filter.

Merlin66 (Ken) · #11 07-02-2006, 12:47 PM

Softly softly. The 80A will probably (??) get some use, but the ND ( unless there's some imaging down the track) will ONLY be used on the moon.
IMHO don't spend too much money at the moment, just enjoy!!!

ThunderChild (Chris) · #12 07-02-2006, 01:02 PM

Quote:

Originally Posted by janoskiss

I said ND only for you because your scope is a 6", so the Moon won't be as bright as in my 8".

Of course.

What about the DGN NBP? What is it? What does it filter?

Quote:

Originally Posted by Merlin66

IMHO don't spend too much money at the moment, just enjoy!!!

Yep - good advice - I certainly don't intend to go out and spend big. But one or two well selected $15 filters would be a cautious way of trying a couple of things.

mickoking · #13 07-02-2006, 09:36 PM

My Moon filter is grey, the moon is still too bright. Sometimes I use the filter on doubles.