Re: [photo-3d] Re: Projector Brightness

["John A. Rupkalvis" <stereoscope@xxxxxxxxxxxxx>]

I'm going to check the polarizers on the
> Realist to see if they've faded or something.
>
> Don Parks

This is good practice for any stereo projector.  Projectors that receive a
lot of use, such as club projectors, should be checked for polarizer fading
at least twice a year, at least until it is determined how long they last in
a specific projector.  Polarizers will last longer in some projectors than
others, depending upon their position, the amount of UV emitted by the
bulbs, the cooling system, etc.  There are many advantages to halogen cycle
type bulbs, but one of the few downsides is that they will fade polarizers
faster, both because of a higher UV output and a higher normal operating
temperature.

Polarizers come in several different densities.  The darker the polarizer,
the more efficient.  Depending on where the particular polarizer density is
on the light transmission curve, this can be significant.  In some cases,
doubling the density of a polarizer can increase the cross-cancellation
capability 10 times.

The best polarizer for a specific projector depends on several factors.  In
general, the brighter the lamp, the more density required for effective
cross-cancellation.  Since only a slight increase in density effects a
considerable improvement in cross-cancellation performance, it still makes
sense to go for brighter lamps, as this gain is only slightly compromised by
a slightly denser polarizer.

Although built-in polarizers are a convenience, if you find that your
polarizer life is too short you may be better off mounting them externally.
Also, this is more efficient, as polarization is not reduced by going
through the glass of the lenses.  This is a relatively small factor, but it
is there nevertheless.

JR


 

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