Hey guys, working on my focusing mech. using threaded PVC. I have about 1.5 inches of movement for the lens, but I am wondering if I need to split that in two so I can move the projection lens both in and out. I know my max screen size (I would never go any larger than that). I would probably want a smaller screen on occasion so I would need to adjust focus in this circumstance.

Here is my question, is the focus adjustment linear for a constant direction? I would like to maximize the amount of focus tweaking I can do so I figured I would place my lense at one extremity and position my focus mechanism so that my picture is in focus at the largest image size I would want. This way I could get a smaller screen size in focus since I have 1.5 inches of focal tweaking but would lose adjustment for anything larger than my estimated largest screen size.

Is this assumption correct?

thanks,
colin

The short answer is yes, the relation of projection size to distance of triplet from LCD to produce a focused image is a linear function.

Great! Thanks