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Discussion Starter · #1 ·
OK, I thought I knew how to do this...


If I have a projector with a F1.7-2.2 on it's zoom lens... I thought you took

(1.7 / 2.2) squared, and end up with 59%. However the typical projector calculators, show 79% lumen output at max zoom, vs min zoom, not 59%. (assuming the exact same size screen is filled, and the only thing that changes is zoom, and distance from projector to screen)


what do I have wrong?


I'm trying to calculate the loss of lumens from going from a standard lens at F1.7-2.2 to a long throw at F2.0-3.5
 

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Discussion Starter · #3 ·
yea, I'd used search, and seen your posts...


HOWEVER, I've used several calculators, and they all show the same results that don't line up with the F/stop formula.


you are saying they are all wrong? somehow that's what I'm having problems with....
 
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