Re: Dissolves for 3-D projectors

[John Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Mon, 27 Nov 1995 16:29:07 -0600
>From: michaelk@xxxxxxxxxxx (Michael Kersenbrock)
>Subject: Re: Dissolves for 3-D projectors

>The fader just needs to be a "thyristor" (actually, a triac or related device)
>with a control circuit that has a decay shape that takes into account the 
>rapid brightness drop-off of a "nominal" projection lamp vs. effective RMS 
>voltage.

It may also need to take into account the hysteresis of incandescent bulbs.
At least with the wall switch dimmers, the brightness of the bulb goes like
this:

                       *
                     *
                   *
                 *
              * *
   (OFF)   *    *
      *         * (ON)
****************

>The projectors and their bulbs would probably need to have a basic match like
>the two halves of a single projector -- at least to the extent of general 
>brightness and bulb type to keep bulb color and brightness matched when 
>switching from one to another without color bias changes.  

The color balance will change at different brightness levels.

Do commercial multi-projector fader systems turn the bulbs on and off?
I'd think all that power cycling would reduce bulb life - maybe a shutter
mechanism (before a diffuser) would work better.

John R


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