Originally Posted by bud16415
You can try it yourself. Take a piece of white paper and hold it to your screen and it will be in focus. Notice the pixel grid as a focus indicator. Now move the paper 3-4’ closer to the projector and see what you get.
Yes that is a quick method to test this to see the Depth of field (DOF)
for the projector setup.
Know from the good old days with CRT projectors that the DOF when focusing the optic can be real narrow 2-3cm, and often used a paper to check the center, corner and Scheimpflug adjustments.
These two projectors (HD1 vs G90) will for example react quite differently to the white paper test (not taking the CRT convergence problems into the equation).
Think Different digital projectors with different resolution Chip/pixel size, throw distance use of lens focal length and Aperture f-number will have different DOF properties. A native 4K projector with almost the same lens and setup like the NX5 vs X7900 will have a quite different size on the pixels and circle of confusion, and that again will be the case between the new JVC 4K models where the NX9 with that great lens will get an even a smaller DOF than the N5/N7 models due to its higher light/aperture setting.
So all of these factors will come to play if the projector is moved or how much the white paper cold be moved before the pixel grid get out of focus.
Actually the focus plane where the projector screen get to be at "100%" (if that exist for a 3chip projector) in focus is only at one particular focus distance, but because of the DOF where the circle of confusion still is small enough to still show the pixel grid correctly there is an usable sliding area where the focus still seems to be ok.
Just tested with a "white paper" on my [email protected]
throw from the 2.35:1 format 120" screen now with and without the A-lens, and can with optimal focus on the screen get about 1' (~30cm) of A4 paper movement shorter throw before it gets out of focus. Switching the A-lens in and out of the light path only reminded me how good and razor sharp that ISCO 4XL realy is...
The "rule" for DOF is that you will get a bigger usable distance further behind the focus plane than in front, (it's about 1/3 in front vs 2/3 behind) so I guess with a slight refocus with this in mind, the total distance cold be about 2' +-1' for that RS520 setup.
If i had to go for a similar variable projector throw setup, I wold try to make it a remote controlled one, maybe build around a slightly modified carport opener or something.
Think a variable projector throw setup is a great idea if the correct projector, zoom and throw distance is used, and it sounds to me like you have a nice one bud16415.
One idea I have played with a little, is to use a shorter throw distance (with or without a necessary lens memory refocus) , is to add a good tab tension remote controlled 16:9 projector screen to my setup.
This is to get the best out of those great movies where there is some variable AR between parts filmed with imax and 2.35:1. So if the screen is situated a little closer to the viewing position, and is large enough, that relay will get that big "imax" feeling, and will be fun to try out.