Due to space constraints, I think the projector I'm going to (eventually) build will have to be moved from time to time. How difficult is it to refocus? If I move it an inch or so will mean hours of redoing settings and frensels? Also, what about variable distances? Would it be feasible to project a 50" image most of the time but blow it up to 120" every once in a while or is that too much of a headache? Thanks for any replies, you guys=awesome.

Chris

this is definitely possible. once you build the projector, you'll probably never move the fresnels again save for a keystoning adjustment or two. focusing is done by moving the projection lens. a general rule is to give the lens two inches of travel--one forward and one back--to allow for focusing. you'll want to read through this thread.

cabbage is correct... but for small changes (1-2') in projector location. If your changing your screen from 50" to 120", then you should be changing your lamp to rear fresnel distance to improve the light distribution.

cheers,
gs

i was unaware of this...guess you learn something every day!

basically for a given lamp and fresnel location, there is an optimal triplet location to maximize light output (or maximize light distribution... it's kind of a user preference which one is more important). If this triplet position is also the position necessary for focus for a given throw, then everything is good. The problem is that if you move the Projector you need to move the triplet for focus. This moved the triplet out of the correct position for the lamp and fresnels... meaning you can move the lamp to compensate for the change in throw, or PJ location.

gs

yeah, i wouldn't have noticed, since i tweaked my projector in and haven't moved it at all since.

Thanks for your replies, so should the lamp be able to be adjusted as well?

Chris