Chromatic Aberration Shift by Throw Ratio?

[Person99]

Obviously, all simple 2 element lenses introduce CA. And the shorter the throw, the worse it is since the greater the angle the light enters the lens assembly, the more change in angle you get when the 33% stretch is applied.

My question is, has anyone plotted the relationship between CA and throw ratio either as a percentage of shift in say blue or as a measurement in something like pixels (i.e. at throw xxx blue is shifted one half pixel at the edge).

So, an example of the application of this would be something like "at 1.6 throw the blue shift is 50% worse than at 2.0 throw." With this, you could then determine things like: at 2.0 throw blue shift is 1 pixel, therefore at 1.6 throw it would be 1.5 pixels.

With all the big brains playing around with this stuff, surely someone has calculated this? :)

[CAVX]

I don't think anyone bothered as most lenses have CA corrective elements in their design, so are more concerned with pincushion and vignetting than CA for shorter throws.

The idea is a good one though, but then again, how many very short throw projectors are there? Then again how many lenses can work at TR of just 1.3:1 - I can think of just two :D

I am about to enter 1080P via a BenqW5000, and it required at least a 4m throw for the same size image I have now. That alone will reduce both CA and pincusion significantly for my system.

Currently my TR (using that Horrid Sony) is [2100mm / (960mm x 1.78) 1708mm = 1.23:1, but that will extend out to 4000mm / 1708 = 2.34:1...

Mark

[syncguy]

Yes, my main concern is pincushioning rather than CA. Also, CA depends on the lens. In contrast, pincushioning could be more generic in most cases (if there is no correction for this).