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nmitsthefish
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Reged: 06/17/13

Loc: Northern Berkshires, MA
Homemade moon filter? new
      #5939006 - 06/25/13 12:32 AM Attachment (28 downloads)

Hey, I'm still super new here and to astronomy in general, has anyone heard of making a moon filter using a lens from the new age 3D glasses they give you in the theaters now? I gave it a shot tonight but I can't test it because it is stormy here. Just wondering what peoples thoughts on this were, or if anyone has tried it. Do you think itll work at all? Here's what I made, can't wait to try it.

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NeilMac
Carpal Tunnel


Reged: 09/25/10

Loc: MedHat, AB, Canada
Re: Homemade moon filter? new [Re: nmitsthefish]
      #5939597 - 06/25/13 11:53 AM

They do warne not to use as "sunglasses" on the package of those theater glasses.

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Ben Therrell
member


Reged: 10/09/12

Re: Homemade moon filter? new [Re: nmitsthefish]
      #5939613 - 06/25/13 12:02 PM

I think your suppression is going to be inadequate. The standard moon filter is 13% transmission and as far as I can tell the glass is nothing more than the Bausch and Lomb G13 sunglass that they developed for pilots during WWII.

The Moon is *blinding* through a telescope and even a 13% filter will still result in some degree of "retina burn" after an extended moon viewing session. You would do better by cutting out some plastic polarized sunglasses. Cut two lenses and by rotating one over the other various degrees of filtration are obtained. I made a Sun filter like that only i used *three* lenses.


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brianb11213
Postmaster
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Reged: 02/25/09

Loc: 55.215N 6.554W
Re: Homemade moon filter? new [Re: Ben Therrell]
      #5939863 - 06/25/13 02:12 PM

Quote:

The Moon is *blinding* through a telescope and even a 13% filter will still result in some degree of "retina burn" after an extended moon viewing session.



This is wrong; the moon is only uncomfortably bright when viewed at night because it is seen against a dark setting. You can view the moon in full daylight but it's obvious the lunar surface is only a little brighter than the daytime sky ... it won't blind you or burn your retina any more than sunlit rocks on the earth's surface will, but the bits of the moon that are projected into the eye will totally destroy dark adaptation, which will recover to its normal value over half an hour or so.

Because magnification spreads out the light over a wider area, the surface brightness of the moon when seen in a scope is never any brighter than it is when seen with the naked eye; it's just bigger. In fact, since magnifications higher than those needed to contain the exit pupil are usually used, the surface brightness is significantly lower when seen through a scope, even if the transmission of the scope is "perfect" (which it won't be even without a filter fitted).

In my experience a moon filter with a transmission in the 13% range is far, far better than none at all (when observing against a dark sky - and for comfort rather than safety) but I do prefer something a bit denser ... I really don't like variable polarisers because of the number of surfaces and the "optical grid" inherent in the polariser scatters more light than either dye-in-glass or dichroic filters. My favourite filter for observing the moon at night is the Baader Solar Continuum filter but, if you want to preserve your night vision as much as possible, you might try a very deep red like the Wratten 29.


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nmitsthefish
super member


Reged: 06/17/13

Loc: Northern Berkshires, MA
Re: Homemade moon filter? new [Re: brianb11213]
      #5940040 - 06/25/13 04:01 PM Attachment (14 downloads)

I figured out with these circularly polarized lenses (3D glasses), if you stack two lenses together, depending on which direction the quarter wave plate on each lens is facing, you can control the amount of light that gets blocked by simply rotating one lens. So now my idea is to affix one more lens on top of what I currently have that I can freely rotate and thus control the dimming "setting" of the filter.

Edited by nmitsthefish (06/25/13 04:03 PM)


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THEPLOUGH
ELEVEN Grandchildren; FIVE Ducklings
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Reged: 01/11/08

Loc: Carlisle, Cumbria, ENGLAND
Re: Homemade moon filter? new [Re: NeilMac]
      #5940356 - 06/25/13 07:36 PM

Quote:

They do warn not to use as "sunglasses" on the package of those theater glasses.





Providing you do NOT look at the Sun with this or any type of home made filter*,I see no harm in trying this on the Moon...


* Unless the proper materiel is used...


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azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: Homemade moon filter? new [Re: brianb11213]
      #5940644 - 06/25/13 11:07 PM

A 13% ND with an Orange W21 is my ideal 8" aperture moon filter for medium to higher mags. I am familiar with the polarizing issues but at the low power I use it when the moon fits in the eyepiece it doesn't hamper contrast. Higher up I don't bother with it but at 70x for example - its a super comfortable filter.

Pete


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nmitsthefish
super member


Reged: 06/17/13

Loc: Northern Berkshires, MA
Re: Homemade moon filter? new [Re: azure1961p]
      #5940749 - 06/26/13 12:41 AM Attachment (13 downloads)

So guys I just constructed an awesome little adjustable moon filter for my eyepiece with two circularly polarized lenses from 3D glasses, it should provide a range of light transmission percentages by simply rotating the top lens "dial". It isnt universal to all eyepieces, i designed it to fit my 25mm eyepiece specifically. Unfortunately it's cloudy and I'm at work so I can't test it on the actual moon but it works great looking at lights through it. (I guess I was unaware that these 3d glasses lenses scratch so easily so there's some "holes" from when I was quickly putting it together but I'm just proud that I came up with this 100% free method of making a variable polarizing filter and I hope it works!)

Edited by nmitsthefish (06/26/13 12:44 AM)


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Ben Therrell
member


Reged: 10/09/12

Re: Homemade moon filter? [Re: nmitsthefish]
      #5940750 - 06/26/13 12:43 AM

That's the formula I used to improvise my solar filter. I taped it over one barrel of a 7x50 binocular and it works very well. I observed the two recent transits of Venus with it.

I was perhaps guilty of hyperbolizing in my former post. What I mean by a "retina burn" is simply an overstimulated retina. If you observe the Moon for a period of time with filtration then look away at an orange mercuric streetlight you will notice that it has reddened significantly because the receptors that gather the shorter wavelengths are overstimulated and not working well.


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