Polarising filter with high transmission?

[acey]

Are there any polarising filters available that transmit more than 50% of light?

[acey]

From a web search I find that Hoya HD filters appear to offer highest transmission, but they're made for cameras (in various standard sizes).

Are there adapters available that enable camera filters to be used with a telescope eyepiece?

[haitch]

I think by the very nature of polarisation you won't get one that transmits more than 50% unless the light is already polarised to a degree.

[acey]

Yes, I realise that how the transmission figure is quoted depends on whether it refers to polarised or unpolarised incident light. The variable (paired) polarisers sold as astro filters are typically quoted as having transmission ranging from 30 or 40% down to 1 or 2%, but it's not stated whether that is for unpolarised or polarised incident light.

My interest in this arises from the following paper which says that skyglow caused by moonlight can to some extent be filtered, because of its polarisation:

http://arxiv.org/PS_cache/astro-ph/pdf/0011/0011005v1.pdf

According to the paper, "Normal polarisers [as used by professional astronomers] are notoriously lossy with typical transmissions of 0.70 (one polarisation state). However, thin polarisers made by 'bleaching' can have transmissions as high as 0.96."

I'm interested in seeing if a polarising filter could be used to assist deep-sky viewing during moonlit nights - hence the desire for minimum light loss.

[haitch]

That's an interesting idea. Too much wine inbibed to read the paper but I think I get the general jist. Sounds strangely plausible.