On February 3, 2019 at 14:44, highfigh said...
Infinity?
Yes. Most projectors throw their image onto a flat surface. A screen, that is. Just as it's silly but accurate to say that DC has a frequency of 0Hz (even this is a rounded-off value), it's accurate to say that a flat surface has a radius of infinity.
Maybe for long throw, but a 7' radius isn't going to work with that type of lens. The image is focused on a plane at some distance from the lens and just like capturing an image, the lens has a limited depth of field. Because of this, a projector that's near its inner limit of useful distance to the screen may be in focus at either the edge or center, but not at the other when projecting its image onto a flat surface. The whole reason curved screens are used is so the viewers will be able to see things in focus when they turn their head or rotate, without their eyes needing to refocus as they turn. The problem- if they're not at the correct locus for the curve, it won't be in focus as it should be and if the lens isn't right for the curve, ditto.
All that is true. And known. And irrelevant because --
You have completely forgotten that this is
art, not video. Choices have been made. Deviations have been made from the way one would focus on, say, "Die Hard." The artist has specified that the center of the image is to be in focus, and it's understood that the focus will degrade as the image gets wider.
How far from the screen is the projector to be mounted?
On the lift that worked with the last projector. The artist has purchased one of these projectors, and the same lens, and has set it up in the studio and defined where it's to go. The throw, at the center, will be about twenty feet.
Remember- the elements of a lens aren't flat, which means they naturally distort the image to some extent. They have corrective elements, but those only work when the lens assembly can focus at a specific range of distances- anything inside or outside of that and spherical aberration occurs. Also, the colors don't have the same wavelength, so it's possible that the same kind of rainbow effect may be seen that's visible with DLP TVs- the colors don't focus on the same plane.
Might I mention something at this point? It's
art. And the artist has physically installed this in the studio and is giving dimensions and instructions from there. The focus has been seen. The change (we'd correctly say "degradation") of focus has been seen. The location of the best focus has been defined.
