Re: Polarizing filters questions

[P3D Michael Kersenbrock <michaelk@xxxxxxxxxxx>]

> 1. Commercial grade w/25% transmission and
> 2. Tech Spec w/38% transmission.

Yes, the Tech Spec stuff looks pretty good.  One of those things
I've been meaning to order when I have the time to do something
with it after it arrives.... :-)

It looks better for more reasons than just transmission percentage,
the other specs that it gives looks pretty good too.  Fortunately
the "sample size" seems big enough, a full sheet is a bit spendy and
a LOT more than needed.  Wish they had some heat/reliability related specs
to go with those other specs.

> Finally, does it make any difference if the filters are placed before or
> after the slide?  If it does not make any difference in terms of light
> extinction then they might as well be placed before the slide to reduce the
> energy hitting the slide.

As someone in our local club discovered, some slides (and/or mounts) 
depolarize the light.  So when his slides were shown at the club meeting
with a TDC projector, it didn't work (you see both pictures with both
eyes).  With a projector like the Compco Triad which has the filters
screen-side of the slides, they would have projected fine.  True, not
a common problem for most people, but it's definitely a problem if
you're that person who has those slides.  Or in a club where there is
a large variety of slide sources.


> To optimize projection condition one has to take into account all the steps
> involved:  Light bulbs, condenser system, polarizing filters, lenses,
> screen, polarizing glasses.  It makes no sense to optimize one and ignore
> the rest.

I agree because this is generally true for most anything in any field, 
however incremental improvements are often possible because the total
performance is often the accumulation of each piece's performance (as
opposed to a chain where the weakest link dominates).


Mike K.


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