Brightness increase using zoom?

Ok so I was just looking at a review for my projector (ae3000) and it talks about loss of lumens when using the maximum telephoto? Does this mean for a given screen size I should have my projector mounted as far back as possible with minimum zoom to achieve max brightness or the other way round?

 

The other way around: Telephoto (least zoom) long throw means least brightness, but most contrast. Can be up to 40% difference between the extremes. My old AE3000 was in a long throw setup and I had to get rid of it as it wasn't bright enough once calibrated (effectively a 128" screen).

 

Is it not just the size of the screen? The smae lumens shared between more square inches?

 

It's this as well, but it's quite possible to have two setups with the same size screen and one could be 40% brighter than the other (imaginery identical projectors ). The one close to the screen but with more zoom applied will make the same size picture, but be brighter and have less contrast purely because of the way that most projector lenses work in changing the aperture when zooming. The one far from the screen, but with no zoom applied, but same sized picture will be darker and have more contrast.

Being aware of this effect can help you to prioritise your setup accordingly: I want to maximise contrast, I like having the projector behind me (like a real cinema) and long throw also helps with an A lens. I chose a screen with enough gain that I would still be able to hit the typically recommended 12-14fL even after lamp dimming, so for me it suits well. In a setup with a shorter room, there may not be the possiblity to do what I've done, or it may even be a temporary setup with the PJ in front on a table. Each has it's pros and cons, so more just a matter of being aware of the effect and how it might effect your setup.

For example, something like an AE3000 really struggles to light up a bigger screen especially in the more accurate modes like Cinema and Colour. Therefore it might be one of these occasions where every last lumen matters so a short throw high zoom setup will maximise the brightness.