Dale J. Chatham wrote:

> The polarizers I've seen for lunar work consiste of two polarizers
> such that one can be rotated to vary the amount of light that gets
> through.
>
> Polarizers are used in photography to darken the sky, since it is
> polarized coming from the sun. I doubt it would have much effect
> looking at a single angularly small object.
>
> Bill Arnett wrote:
>
>> I've heard of a few people who use polarizers when viewing the Moon.
>> But I'm not sure if it's any better than a ND filter (and I'm not
>> sure either is better than nothing :-)
>>
>> On Nov 17, 2004, at 5:52 PM, R. A. Greiner wrote:
>>
>>>
>>> I have not seen any response as well.. I think the reason is that
>>> there is no point whatever to using a Polarizer for visual
>>> astronomy. Polarizers always have some substantial light loss. The
>>> biggest fight in visual astronomy is to gather light. As it is,
>>> even with large telescopes, say one meter and above, the light from
>>> many objects is so dim that they can only be seen by averted vision.
>>>
>>> I have never heard of anyone using polarizers. That perhaps the
>>> reason for no responses.
>>>
>>> Even in CCD astronomy you need all of the light you can possibly
>>> gather. What would be the reason to through away some light? I can
>>> think of none.
>>>
>>> Doc G
>>>
>>>
>>>
>>> ----- Original Message ----- From: "Bill Keicher"
>>> Sent: Wednesday, November 17, 2004 5:46 PM
>>> Subject: Re: [M]: Use of Polarizers In Visual and CCD Astronomy
>>>
>>>
>>>> John,
>>>>
>>>> We are still waiting for any input.
>>>>
>>>> Bill Keicher
>>>>
>>>> At 09:10 AM 11/17/2004 -0400, you wrote:
>>>>
>>>>> What response did you get for your posting. Can you share them
>>>>> with me.
>>>>>
>>>>>
>>>>> John H Fraser
>>>>> Cape Breton Astronomical Society
>>>>>
>>>>>
>>>>> ----- Original Message ----- From: "william mccarthy"
>>>>> Sent: Wednesday, November 17, 2004 6:21 AM
>>>>> Subject: Re: [M]: Use of Polarizers In Visual and CCD Astronomy
>>>>>
>>>>>
>>>>>> Linear or circular?
>>>>>>
>>>>>> Bill
>>>>>>
>>>>>>
>>>>>>
>>>>>> At 01:21 16/11/2004, Bill Keicher wrote:
>>>>>>
>>>>>>> Polarizers are used in outdoor photography to increase color
>>>>>>> saturation. Polarizers can make the clear sky look deep blue by
>>>>>>> reducing scattered light that is polarized. The magnitude of
>>>>>>> this effect depends on the relative positions of the sun, the
>>>>>>> observer and the object observed.
>>>>>>>
>>>>>>> Has anyone used this technique to reduce the sky background
>>>>>>> level caused by scattered moon light or localized city light?
>>>>>>> Even though a polarizer would reduce the light from an
>>>>>>> unpolarized source by at least half, It seems like using a
>>>>>>> polarizer would improve image contrast under certain otherwise
>>>>>>> unfavorable conditions. Seems like it would be worth trying.
>>>>>>>
>>>>>>> Clear skies!
>>>>>>>
>>>>>>> Bill Keicher
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>>
>> --
>> Bill Arnett
>> Emerald Hills CA USA 37 27 N 122 15 W
>>
>
Dale, Sorry to rain on your parade but light from the sun is NOT
polarised. How could it be? The rotating twin polarising filters you
speak of will cut out ANY light when the orientation of the two linear
polarising filters is at 90 degrees to one another.

Please try to check your facts before spreading mis-information.

regards
Gary

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