Re: preliminary summary on ghosting2

[P3D Steve Spicer <s.spicer@xxxxxxxxxxxxxxxxxx>]

>From: P3D Peter Abrahams  <telscope@xxxxxxxxxx>
>There has been a good amount of input on ghosting, and this is a first
>attempt at summarizing it for the archives.  Comments and additions are
>solicited.


Thanks Peter

Your posting was timely as I just been playing around with shifting the
polarisers in my projector, and trying out some HN38 polarising sheet I got
from Polaroid. (HN38 - that's 38% transmission when parallel).

I have got some data sheets from Polaroid on linear polarisers, and was
surprised at the large number of types available. I have scanned some
graphs published by Polaroid and put them on my Web page at:

http://werple.net.au/~kiewavly/polariser.html

One effect I did notice when making the frame to hold the 0.7mm thick
plastic polariser was that the polarisation degraded near the screw-hole
that fixes the polariser in position, and it was worse if I did the screw
up tight. It doesn't really affect the on-screen polarisation as it only
affect a very samll area of the polariser, and this was outside the main
light path.

When I first built my projector I had the polariser as the last item in the
light path (outside the projector casing), but have recently moved it
between the condenser and slide (because in doing so I can remove one of
the two heat filters in each condenser system giving about 1/3 stop more
brightness, and over-run the lamp voltage to get about another 1/3 stop
brightness.) That adds up to 2/3 of a stop, although I think I am not
getting quite as good extinction now.


>
>--anybody tried 'research grade Polaroid', or is there such a thing?
>

It could be the HN42HE product described in the graphs.

Steve Spicer





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