Why moon filters ?

[John]

I see loads of posts recently recommending moon filters for scope apertures of 6" and above. They seem to be considered almost essential equipment now.

I've owned 20+ scopes of apertures ranging from 60mm to 305mm but I've never felt the need to use a moon filter.

Yes, the fully illuminated lunar disk is bright with a larger aperture scope, but I find my eye quickly adjusts and there is no danger of eye damage from lunar illumination as far as I know.

As my eye adjusts, I find that I can see subtle contrasts in lunar surface colour and texture "unfiltered" and I can see 4 of the Plato cratelets with my 4" refractor when the illumination is right, more with my larger aperture scopes.

I'm wary of putting anything in the optical train that does not serve an essential purpose so what am I missing by not using a moon filter of some sort

[nicnac]

if find it a must to be honest John but thats because my eyes are overly sensitive, i tried viewing the full disk a few times before i got the filter in the hopes i would get used to the brightness but it just fealt as if somebody had blown pepper in my eyes every time.

i purchased the variable, which is just that, just to cut the burn some, i have noticed that it sharpens the views some too i have had some great detail when using the filter, which is not bad considering i could barley look at the full Moon before.

do you think you could borrow one for your own testing?, see if you can see any difference yourself, i think you may be happy with what you see in difference

[Shibby]

I personally find the moon extremely bright too - it hurts for a couple of minutes until my eyes eventually adapt and put up with it, but then your night vision is shot for a while.

Saying that, I can never be bothered to attach my moon filter!

[Doc]

I have often viewd the moon, even a full moon through my 16" before with no filter, my eyes seem to adapt very quickly and I find it alright.

I only observe Lunar when the moons out so don't require dark adaption anyway.

I do have a neodydium filter which I sometimes use which does dim it down but I think at the expense of some contrast.

[twotter]

I use a moon filter because I prefer to. The unfiltered view is bright enough to be uncomfortable, for both my wife and for me. Using the filter makes observing easier for us, whilst still allowing us views of the Moon which make use go 'wow'

Anyway, if I didn't use a filter I'd have to wear sunglasses

[Merlin]

I've found that the best time to view the Moon ( and the brightest planets ) is while the sky is still light, i.e. in twilight conditions. The lighter sky reduces the glare of the Moon, making a filter unnecessary.

[BinocularSky]

Never use the things -- just something else to get dropped, dirty, lost, etc. The Moon is no brighter in a dark sky than it is in a light sky, so I don't see any reason for a filter -- the eye soon adapts.

there is no danger of eye damage from lunar illumination as far as I know.

Exactly correct.

so what am I missing by not using a moon filter of some sort

Something else to scrabble about in the grass for before treading it into the ground.

[johninderby]

I've never used a regular moon filter as I've never had any trouble adapting to the brightness of the moon. I do however use the Baader Moon & Skyglow filter as I find it gives the moon a nice neutral grey colour and seems to improve contrast a little bit.

I do realise though that some people do have light sensitivity problems that might require them to use a Moon filter. This link explains the subject of light sensitivity pretty well.

http://www.allaboutvision.com/conditions/lightsensitive.htm

John

[John]

Interesting range of views and experience folks - thanks for posting .

My conclusion is that the advice to newbies should perhaps be you may find you need a moon filter rather than listing it as a "must have".

[smudgeball]

Thanks for an interesting post.

After last night I'm considering purchasing a moon filter.

I was trying out my new hyperion 13mm and the contrast and detail of the moon was far better than my "kit" EPs.

Although, more comfortable, I still found it a little bright so will most likely get a filter.

But nice to see some differing views.

Neil

[Luke]

I don't always use a moon filter for the moon but when I do it's for two reasons mainly:

1) In the big dob the full moon can be painful to look at for me at first, I guess because my eyes have adapted to the dark. Even a bright laptop screen can hurt my dark adapted eyes!

2) Looking at a bright moon can mess with my eye's dark adaption! When it is really bright in the dob, after I've been looking for a while then walk away with both eyes open, it is really weird, it feels like I am wearing a pirate eyepatch for several mintues! If I was only observing the moon that's not so bad I guess but if I want to shoot off to look at some DSOs it does KO my viewing eye for a while!

[bish]

I tried one once but didn't like it so never use one. As with others my eyes get used to the brightness almost straight away

[Mak One]

Interesing thread. With the 150 MAK and the SW 28mm 2" e/p the full disc of the moon just fits the FOV. When the Moon's full it is extraordinarily bright in this set-up. I find viewing like this is possible (if uncomfortable) but leaves me with a persistent bright image in my open or closed viewing eye for many minutes afterwards (akin to the "pirates eye patch" feeling mentioned above).

I get about the same FOV with a 1.25" 32mm e/p as well, but I can fit the moon filter to this and look at the Moon for extended periods, studying fine details in higher power e/p's, without significant detriment to dark-adapted eyesight.

If the Moon is a thin crescent, or in twilight/daylight, I don't bother.

The filter also helps when imaging the Moon as it tones down the very bright areas around the terminator. This allows more detail to come through, otherwise I found I was turning the capture settings down so low to avoid the worst of the over-exposure that I'd miss the detail.

So I'd say a filter is a good thing, but maybe not a "must-have". Each to their own...

[brianb]

Well it's not necessary to protect the eyes from damage but the moon certainly can be uncomfortably bright when viewed in a dark sky. A deep red (Wratten #29) filter makes it much more comfortable when the sky is dark, increases the contrast against a twilit sky (even when the sun is above the horizon), preserves most of your dark adaptation and the seeing is steadier at long wavelengths ... win, win, win ... can't imagine why anyone would want to be without. The moon is essentially colourless so there is little to be lost by using a deeply coloured filter; some people prefer green but red works better for me.

[Mak One]

Brian

So would a #25A red do the trick? (the red from the Rev Astro set?)

[brianb]

would a #25A red do the trick?

Better than nothing, for sure, but the #29 is far superior in retaining dark adaptation & enhancing daytime contrast.

[calibos]

No one is arguing that viewing the moon in a big dob is dangerous or that its any brighter when viewed against a black sky or blue but surely anyone can understand that even partially dark adapted its going to be painful for a while without a filter. Think about waking up in the night and switching on the light in the room. Is looking anywhere near the lightbulb dangerous? Of course not. Is it painful/irritating? Yes!

Has no one experienced moon blindness? After getting dark adapted and then looking at the moon unfiltered I can't see a thing with bright coloured blobs in my vision for a few minutes afterwards

[ollypenrice]

20 inch Dob with enough field for the full disc is not a pleasure, unfiltered! It does not feel good and the body is usually competent at telling you what is and is not a good idea.

If nothing else you might, duly de-adapted, walk into a prickly rose bush or stand in some canine calling card!

I must try the red instead of ND though. I can see the logic.

Olly

Sorry Calibos, we crossed there. Didn't see you though, had the 35 inch on the moon last week...

[nicnac]

some say "your eyes adjust" and some will, mine do not adjust enough so im on the filters

[tomw28]

For me the filter is essential. Without it is both uncomfortable on my eyes, as well as giving me a headache after a while. While I agree that the view isn't quite as nice, the comfort is worth the slight loss of image quality in my opinion.

[BinocularSky]

A deep red (Wratten #29) filter makes it much more comfortable when the sky is dark, increases the contrast against a twilit sky (even when the sun is above the horizon), preserves most of your dark adaptation and the seeing is steadier at long wavelengths

Interesting -- I must try it. Just one thing -- do you have red goggles as well? because just looking at a bright Moon with the unaided eye is sufficient to hammer my rhodopsin...

[johninderby]

After reading up more on Photophobia (light sensitivity) it seems that people with light coloured eyes are more susceptible. I wonder if there is any correlation between those that have reported needing to use moon filters and those that haven't?

There are other causes for Photophobia of course but it made me wonder.

John

[nicnac]

interesting John, i have pale blue/grey irises (if your taking a tally )

[Hypernova]

I tend to experience sensitivity to bright sunlight, it doesn't have to looking near the sun but usually into a bright blue summer sky is enough t cause me discomfort and my eyes to squint and water a little. And saying this I do tend to suffer some discomfort when viewing the moon through the 8" dob because it is so bright, it is worse at lower magnifications when I have more of the disk in view but I have felt a pain when using my 7mm ortho on Sunday night.

I do tend to use a moon filter when observing the moon because it tones down the brightness to a level I can comfortably tolerate, I haven't noticed any loss of contrast when using one, probably because I am not a big lunar observer and don't necessarily go looking for the fine details. The filter I use is an Antares ND 13 if that is any help.

BTW I have brown eyes so I don't really all into the "most at risk" category for photo sensitivity

[great_bear]

Interesting -- I must try it. Just one thing -- do you have red goggles as well? because just looking at a bright Moon with the unaided eye is sufficient to hammer my rhodopsin...

I've been using a #29 red filter on the moon since BrianB recommended it to me on [*ahem*] a certain "other" astro forum we know, some 18 months ago.

When seeing is poor (or probably more accurately the scope is too warm) the red filter cuts right through it and provides solid views. Even when used in good conditions the monochromatic, long-wavelength view seems to have more fine detail than the unfiltered view.

Of course, a red moon is not to everyone's taste.

If I'm brutally honest with myself, although I've got various filters to "experiment" with, only the

• #29 Dark Red (for moon), and
  
• Orion Ultrablock (for nebs)
  

- get regular serious usage as working tools. The other filters that I have are just superfluous "theoretical" toys, and their lack of daily use would indicate that they're really not needed.

I have red goggles too - these are for when I go back into the house for tea

I'd certainly not want to be without my #29 Dark Red for the moon!

(even though I don't always use it)