More on projectors

[P3D Dr. George A. Themelis <DrT-3d@xxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Eric G. writes:

>different lenses often have different *speeds*. I have
>seen 50s stereo projectors with f/2.2, f/2.8, and f/3.5 lenses. These
>aperture differences do make a noticable difference in screen brightness
>(a question posed in your part III), easily as much as switching between
>500 and 750 watt lamps...

Sounds reasonable, however after a brief discussion with Colin Clay
I am not sure if the aperture ratings of the projection lenses have
the same interpretation as those of camera lenses, i.e. a f/2.8 lens
transmits twice as much light as the f/4, etc...

>George, do you know if TDC 4" and 5" lenses are of the same speed?

Yes, they are all rated f/3.5

Another interesting discovery:  The TDC and Compco Triad lenses are 
fully intercheangeable.  I used a pair of 4" lenses from a Compco 
projector in my TDC and it worked fine.

George Themelis


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