Originally Posted by mark haflich
Thanks Mike. I couldn't remember torus. I edited my post.
So let's sum it up. If you add a horizontal stretch anamorphic and do a vertical scaling stretch on wide screen material, you get about 25% extra brightness to light up your screen. This will increase the brightness to your eyes about 6%.. That's about the total positive.
The negatives some of which can be ameliorated by ideal set up and a curved screen but not eliminated are:
A 5% loss in ANSI contrast
The negatives effect of scaling vertically with a non simple scale ratio
An almost complete loss of depth of field with consequent effects on screen focus as one moves away from screen center
Geometric pin cushioning.
Standard screen radiuses are not curved enough for most throws.
Pin cushioning will be ameliorated with a curve screen but to hide all pin cushioning the image will have to be over scanned eliminating part of that precious extra light the anamorphic gives you.
Spherical or rather circular anamorphics perform best when the entry image is small and this optimized requires set up at long throw.
If you starts with a projector that does not have a really good lens, the deterioration caused by the anamorphic glass is I suppose tolerable. With a great projector lens, an anamorphic will throw away some of the lens performance you are paying for.
To minimize this, one should use an expensive ISCO anamorphic and use optimum set up (long throw) and a curved screen although the ideal curved screen with need a custom curvature rather than one of the two off the shelf available.
I am sure I am missing other things.
If you decide to use an anamorphic for whatever reason, If you are starting with a 4K projector, you need a really expensive anamorphic rated at 4K and horizontally stretching at 1.25 instead of 1.33. Regardless of display resolution, one should use a curved screen and use as long as throw as one has available and the projector permits. If brightness is a problem employ screen gain in moderation (I would not exceed 1.3) and as necessary reduce screen size.
Please feel free to modify this list and correct any errors I may have stated.
In my day I have sold many anamorphics and have installed many. Most have been ISCO's and all have been at close to longest throw with and with out a curved screen. The results have been good but with compromised set up, I don't know.