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Hi peter,

I tried searching and couldn't find the posts.

My concern with using two polarising filters is that the UV may behave
differently and not be polarised, so although the optical light is
diminished, the UV comes through just as before!

One solution I'm considering is using solar filters for astronomy and
I quote (http://www.greenwich-observatory.co.uk/acatalog/
Solar_Filte.html): "BAADER AstroSolar film has become the natural
first choice for white-light solar observation. It's optical qualities
are excellent, enabling you to see high-resolution images with a
natural colour."

Only problem is that it doesn't say how much the light is attenuated
and although it ought to be suitable, I've no way of checking out
before hand.

The other alternative I'm considering is buying some sheets of optical
filters - unfortunately with no guarantee on UV transmission so only
for lunar work (is there any significant UV in moonlight?).

Mike

On Nov 21, 8:10 am, "Peter Fogg"  wrote:
> Greg R
>
> Check out the List archives for discussion on using polarising filters. If
> you use two in series they can be rotated for increasing combined density,
> right up to total.
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