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Re: TDC vs. Triad - Stereo Projectors


  • From: P3D Michael Kersenbrock <michaelk@xxxxxxxxxxxxxxxxxx>
  • Subject: Re: TDC vs. Triad - Stereo Projectors
  • Date: Thu, 11 Sep 1997 15:30:46 -0700

> >Was it actually concluded that "harmful radiation" falls upon the image
> >w/o having a polarizer to protect it?  I recall it being more like
> >"just in case there is a problem, having it polarized seems a safer bet".
> 
>   For the same screen brightness having the polarazers
> before the slide will expose them to less light than
> having the pol's after.
> 
>   The typical polarizer passes 38% of the light, so
> a system with the pol after the slide will expose
> it to roughly 2.5 times as much light for systems
> that have the same screen brightness.

True.  But:

	1) It wasn't clearly determined that damage to the slide was
           predominantly caused by light levels.  Dominant mechanism could 
           be something else.

	2) Brightness isn't clearly the same.

	3) Whatever the breakdown mechanism is, it might be polarization
           specific so the filtering *might* not make any difference.

	4) The energy spectra between the projectors may be different
           due to things like the glass elements being of different
           design or composition.  The dominant slide breakdown mechanism
           may occur as a function of the spectra, and the spectra may
           be different (esp. at infrared).

	5) Some TDC's also have 750W bulbs and this may add another
           factor.  There may be significant differences between
           units.

	6) It isn't clear how in *actual* typical use whether the
           longevity of a slide is primarly determined by what 
           projector is used (as opposed perhaps to just age and
           humidity being the predominant factor).

	7) All of above also probably is different for each film
           studied.

	8) For heat mechanism purposes, it also varies by mount (like
           "no glass" being "better").

This isn't to say that the Compco doesn't fry slides at ten times the
rate of the TDC, but it isn't so say it isn't the other way around either
without fully understanding the breakdown mechanisms and contributions to
the rate of each mechanism.

This is why I had only concluded from previous threads that:

"just in case there is a problem, having it polarized seems a safer bet".


Mike K.


P.S. - Of course, it could be that I just wasn't paying proper attention.  :-)


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