Originally Posted by SHIFTTOO
Mark, Thanks for the response!
Is there any way you could elaborate on why a cylindrical A-lens would be my only option. Forgive my possible ignorance on the topic. But does a cylindrical lens produce less pincushion or other visual distortion at a low throw ratio? Or is it some other reason.
Prism lenses require the prisms to be rotated, so the wider the stretch, the more rotation. This can make the prism lens quite deep.
Short throws mean wider beam angles, so the issue is being able to pass these beams through the lens or adapter and not vignette (clip the beam).
Above is a very simple diagram of both a cylindrical lens and a prism lens. The angle is calculated to represent a TR of 1.3:1. Note that the prism adapter is quite deeper than the cylindrical lens and that the beam clips at the top of the front prism.
I realized after posting that have drawn the cylindrical lens slightly wider than the prism lens, however in a real world example, that won't give it any real advantage as the real advantage comes from the ability to change the air gap (blue arrow) between the optics. Prisms lenses are fixed and you can not change the spacing.
Rule of thumb: The shorter the TR the smaller the air gap and therefore the smaller the distance from front to back of the lens.
Hope that makes sense.