Thursday, July 15, 2010
Projector Lens and Focal Length
Yesterday I borrowed the Substation's projector and took it home to check out its specs. The model is a ViewSonic's PJ503D DLP.
Brightness: 1500 ANSI Lumens
Size: 26.42cm x 10.92cm x 21.84cm
Projection Screen Size (Diagonal): 96.52cm ~ 381cm
Throw Distance: 5ft. ~ 19.7ft. (1.52m ~ 6m)
Throw Ratio: 2:1
Vertical Keystone Correction: +/- 7 Degrees
Lens Aperture: F/2.57
Focal Length: 22.2 mm
Resolution: 800x600
Bin gave me a link to calculate the Projection Lens: Projection Lenses Questions and Answers with formulae.
Unfortunately after playing with numbers for a while I realised that my mathematics is a failure. I have to admit I didn't even take mathematics at 'A' levels. Good lord. But fortunately, there are things called calculators. So in the end I gave up fiddling about with the stupid numbers and found an online calculator:
From these calculations it seems to suggest my projector may not cover the whole surface if i want to keep it focused and I get a throw distance of 2.13. But what difference will a mirror make to the projection? I do not know... As a lot of things have already been set in motion, there is nothing to be done but to test the projector setup on Sunday.
Another link which might be helpful in understanding projectors is: HTRGroup's Projector Facts
Footnote: After testing it on 25th July, it became clear that apparently i needn't have worried as focusing the projector was a breeze, with a flick of the focusing dial on the projector. With a mirror setup as the projection throw is bound to be over 1.5m anyway due to the size of the box.
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