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Variable polarising filter


slowhand

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Just something you might find interesting.

I was watching a video on youtube by Robert Dalby of The Astronomy and Nature Centre in which he gave a tip for using the variable polarizing filter. I myself have one of these filters which I find excellent but last night was the first time I used this tip.

I have a skywatcher 127 and if you seperate the two polarizing filters and screw one into the tube end of the diagonal and the other in the EP then you only have to turn the EP to alter the density. You can also put one of the polarising filters in a Barlow instead of diagonal.

Slowhand

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  • 1 year later...

Hello all,

I was reading the mail on variable polarizing filters. I'm just curious as to the benefits. I've been experimenting with some filters.

the varialbe polarizing filter didn't ring any bells with me. I'm new on the subject.

Dennsi

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The other potential application would be to reduce scattered moonlight (or indeed sunlight) on the sky background since these are polarised. The maximum effect would be at 90 degrees from the Moon (or below-horizon sun at twilight). It was proposed in a research paper (link below) and I gave it a try, in case it might be of benefit for DSO viewing - but the polariser cuts at least half of all incoming light so you don't get left with much of a view. Hence as a "moon-light pollution filter" or "twilight filter" it has only limited value.

http://mnras.oxfordjournals.org/content/322/1/201.full.pdf

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Like BigMak, I use one for the Herschel Wedge but it is Baader's 1.25" single stacked version which has a variable transmission - by simply turning the eyepiece - between 1% to 40%. I find it absolutely essential when viewing the sun but on bright solar system objects I've had a mix bag of results.

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