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

See this post (http://www.avsforum.com/avs-vb/showthread.php?p=10260206#post10260206).

And this one (http://www.avsforum.com/avs-vb/showthread.php?p=10262255#post10262255).

In fact, read that whole thread. ;)

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....