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John

Why moon filters ?

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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)

Edited by great_bear

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I have tried various moon filters and never got on with them. they shift the focus quite a lot and seem to reduce clarity slightly. I have not used one for ages, viewing the moon comfortably (after a minute or two of looking) but comments on the Baader Neodymium filter made me buy one used. I prefer the unfiltered view when the moon is 50% or less but when more illuminated I prefer it with the filter. I agree it provides a really nice neutral grey tone and seems to enhance contrast for me anyway.

I have no intentions of buying a filter for use with my 16" when this is completed but will report back if I remember!

When you finish your 16" project you could always get a pair of these for lunar observing. ;)

http://www.rapidonline.com/1/1/18511-gas-welding-goggles.html

John

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ha ha - already got a pair on order ;)

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A very interesting discussion, John. Thanks for posting. It's something I've often thought about too.

Personally, I'm in the "Why?" camp. I have never felt the need for one, even with a 16" dobsonian. It's bright, but the eye adapts. Yes, afterwards you have a blind spot for a minute or two, but for me it's not worth the hassle.

I am very sensitive to bright light with my left eye though - it often streams when I stare at a bright daytime sky.

In any case, I think it doesn't do any good to allow beginners to think it's one of the first things they should buy, as that money would be far better spent on other items: a red torch, a sky atlas, an improved eyepiece....

Andrew

Edited by Andrew*

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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".

The only time a filter is used on my scope is when I am showing the Moon to someone for the first time, as not to startle them with the brightness :o

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I don't use a moon filter even though I suffer from light sensitivity - but then I only have a 130mm Newt and mainly do imaging.

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I'm not very experienced, but have tried with and without - can't find a reason to favour either if I'm honest.

A dark red filter wouldn't bother me in the slightest and something I might try (when I get rid of my old Celestron EP set wit the filters).

The red goggles mentioned in the responses sound a blast though ... a bit X-Men ...

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Very nice!

They remind me of goggles you randomly see someone wearing in some post-apocalyptic Hollywood effort.

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There are ways round the problem for anyone with sensitive eyes without resort to a filter. You can reduce the light coming into the scope by partially covering the aperture. Some scopes have a small offset cap on the ota lid for that purpose.

Also I'm toying with the idea of magnifying the effects of the atmosphere with a naff standard issue barlow to dim the moon down a bit - deliberately spoiling the view to make it viewable appeals to me in a wierd way lol ;)

Edited by brantuk

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Filters - meh...

The whole idea of a large aperture is to get as bright and contrasty image as possible. With a filter, black is still black, white becomes grey and grey becomes dark grey. So what you have is much reduced contrast, a big 'no' when you are looking for fine detail.

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Just to go back to a point about photophobia.

It can depend on the colour of your eyes. If your eyes tend towards the blue then light is reflected far more easily within the eye which can be very uncomfortable. It's not necessarily 'photophobia' as your eyes just have those properties. So for some, filters will be necessary. Whether the views are better, I will leave up to other people ;)

Steve

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You can reduce the light coming into the scope by partially covering the aperture. Some scopes have a small offset cap on the ota lid for that purpose.
At the expense of resolution. Filtering is a much better way to reduce light intensity. Why buy (and lug around) a 8" scope and use only 2" of it? Edited by brianb

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I got an ND0.96 filter when I bought the scope as it was a 'recommended' accessory, but I found it unnecessary and irritating so never bothered with it, (I have dark brown eyes). One of Moonshane's posts in another thread talking about using Neodynium filters for the moon sounded interesting so I tried it and found the view very much improved. As others have said, the surface colour and contrast just seems to make the details pop for me.

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Fair point Brian - just an idea really for light sensitive observers - personally I rarely if ever block the aperture, and I've never felt the need to use filters on the moon - but then I only view when its half or crescent - much more interesting ;)

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This thread reminds me of other threads discussing eyepieces in that not everyone sees things the same way and what's best for one isn't necessarily the best for someone else. A lot of discussions about what is the best eyepiece, filter etc seem to overlook the fact that there can be considerable differences in peoples vision.

John

Edited by johninderby

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Well I find looking at a half moon a problem with my 8" and only using 2" of it. So I cannot fathom how some people can observe through a 16" and get on with it okay. I guess I wish I could do that but then perhaps it isn't healthy for the eye?

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I have a ND96 moon filter which I use when ever I look at the moon from half to fulll as I can't see the point of dark adapting only to spoil it.

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I rather like the thought that, as a group, we have different ways of approaching this. We're all happy with our own way of doing things, and I must say, I rather like being a bit different ;)

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Having wondered myself about the benefit of a moon filter, I found a group of filters on sale at the Meade online store a few weeks ago, while looking at 'close out' plossls. I'm sure it is the least expensive Meade version, but, I tried it over the last 2 nights with a variety of lens & Barlow combinations and was thinking of how disappointed I was with the loss of fine contrast! But, later on in the evening-after I had put most of my stuff away, I still had a 70mm refractor out & 1 pair of of 20x80 tripod mounted binoculars-I glanced through the scope with a 15mm Plossl mounted (no filter), got stuck there for a few minutes finding and observing the remains of an unbeleivable image I noticed the night before on the sun/dark edge and then stood up! Well, I hope pirates adapt better to eyepatches than my lack of vision impaired me!

Funny side note- Earlier in the evening, I grabbed my Celestron 7mm to 24mm Zoom (with moon filter mounted) from my refractor and popped it into my larger (Meade DS-2114) 'scope and thought that I had left the lens cap on! Usually pretty good at grabbing any ambient light and certainly smaller, dimmer stars in the FoV-I was dismayed, until I realized that I left the filter on!

The jury is still out on contrast, but, I never used one before this week's viewing. For now, I think I'll keep using it with various magnifications on both types of beginner 'scopes. I too, drop things and then step on them-even with the red lit headband turned on!;)

Dave

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I destroyed my eyes many years ago welding so my pupils do not dilate, so I use 2 moon filters and sunglasses to look at the moon, I even wear sunglasses to view Saturn.

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I use a variable polarising filter whilst observing the Moon . During the differing phases i find that being able to adjust the light transmission very comfy . In my opinion i don't feel that i loose any detail or contrast that spoils my enjoyment.

As a few have stated , i find that the brightness of an unfiltered Moon is uncomfortable and forcing my eyes to get use to the light intensity unnecessary . My eyes are Blue / Grey and don't yet require glasses ( unsure if that makes any difference ).

Good thread though and interesting to see peoples views.

;)(Variable filters!)

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I borrowed an 8" Dob from Cotswold AS last night to compare to the 5" refractor I normally use for observing the moon and I found something I didn't expect. While observing (no filters) the view was great, nice sharp, better contrast than I expected, really very nice. This morning my eye feels all gritty and sore for the first time ever. The only thing I can put this down to is the extra aperture...

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but comments on the Baader Neodymium filter made me buy one used. I prefer the unfiltered view when the moon is 50% or less but when more illuminated I prefer it with the filter. I agree it provides a really nice neutral grey tone and seems to enhance contrast for me anyway.

This is exactly how I use the Neodymium filter. I find using it when the moon is a small crescent there is not enough light to get a good view.

However when the moon is reaching full the filter helps to bring out detail.

The only other time is when attached to the 36mm, 2 inch eyepiece to increase contrast and reduce the light pollution glow a bit when observing from my back garden. viewing globular clusters and such seem to pop into view easier when star hoping to find things.

Edited by MjrTom

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