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I love the idea of trimming brightness with a polarizer. But you can't rotate a binohead like you can an eyepiece (not unless your eyes move around in your head). With aggressive tube shortening you *could* use double diagonals (sort of like a bent refractor), and rotate the wedge with respect to the other diagonal. But you might find that the correct rotation still left the binohead in an uncomfortable position.

Something like Meade's variable polarizer (with the fixed element removed) might work better, but it's 1.25"...

Any other ideas?

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Hi Jeff,

Since variable polarizers use two optically identical polarizers, typically both in threaded cells that will fit a standard threaded 1.25 inch eyepiece barrel, for my binoviewing I just add them individually to each eyepiece and rotate the eyepieces to matching brightness levels (very easy to do). This is a lot less hassel, and no extra stuff to buy...

Note the internal threads on the "fixed" polarizer on the left to accept the threaded rotating element on the right -- they are all identical to the standard 1.25 filter thread, and therefore each will fit a standard 1.25 inch eyepiece.

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Bob Yoesle

You are a child of the universe,
no less than the trees and the stars...
And whether or not it is clear to you,
no doubt the universe is unfolding as it should.

Desiderata

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OCS read glasspath compensator... T2 system chart... part number T2-03, which is different from your T2-27. T2-03 is a step-up ring (from M36,4 to T2), while T2-27 is a step-down ring (from UNC2" to T2). So the question is, does the step-down ring have internal threads (M34) for the glasspath compensator, or is it the right diameter (38mm) for the teflon centering ring that comes with the glasspath compensator? The chart only list the filter threads (M48) on the input side.... there's also T2-28, which goes from UNC2" to T-2, but doesn't have the lip in between. This one doesn't indicate if its internally threaded on either side.

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AARRRRRRGHHHHH!!!!!!
ENOUGH!!!!!

Wes

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Bob --

I thought about that, but I thought it'd be hard to keep both eyes at the same brightness. But perhaps that's not really an issue in practice?

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Actually Jeff, you may find, as I have, that the brightness sensitivity of your eyes may vary. While not as bad as the pirate above, my right eye is not as sensitive to light as my left, and the ability to individually adjust / fine-tune the brightness for each eye is of benefit for me when binoviewing. Even if both your eyes are equally sensitive, getting the brightness level equal with two polarizers is very easy - try it. Adjust the brightness for your dominant eye first, then your non-dominant eye.

I also suspect that when I observed the sun for years while a kid through a cheap eyepiece-mounted welders-glass type filter some IR or UV leaked through, and my right eye is about a magnitude less sensitive than my left (non-dominant) eye. Another reason I'm Mr. Overkill whe it comes to IR/UV protection...

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Bob Yoesle

You are a child of the universe,
no less than the trees and the stars...
And whether or not it is clear to you,
no doubt the universe is unfolding as it should.

Desiderata

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Actually Jeff, you may find, as I have, that the brightness sensitivity of your eyes may vary. While not as bad as the pirate above, my right eye is not as sensitive to light as my left, and the ability to individually adjust / fine-tune the brightness for each eye is of benefit for me when binoviewing. Even if both your eyes are equally sensitive, getting the brightness level equal with two polarizers is very easy - try it. Adjust the brightness for your dominant eye first, then your non-dominant eye.

I also suspect that when I observed the sun for years while a kid through a cheap eyepiece-mounted welders-glass type filter some IR or UV leaked through, and my right eye is about a magnitude less sensitive than my left (non-dominant) eye. Another reason I'm Mr. Overkill whe it comes to IR/UV protection...

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The etalon in a H-alpha 'scope polarizers the light also, so using a polarizing filter in the eyepiece works well to adjust the brightness and improve the contrast. I use one all the time on my PST.
Any time you have a reflection off of bare glass the light has some level of polarization. The closer the angle of reflection is to the Brewster angle the higher the level of polarization. For crown glass the Brewester angle is about 57 degrees. Antique solar prisms use two surfaces angled at the Brewster angle and one rotates one prism with respect to the other to cross polarize the light and dim the image. With both surfaces at the Brewster angle, the light is fully polarized and one can fully dim the image to full blackness.

- Dave

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