Quote:

Originally Posted by

The improvement is vast. A cylindrical can be designed to do almost whatever you want, given enough curved surfaces. The more the better.

Prisms respond in one way only: no matter what angles you use in the prisms themselves, there's a performance bottom line that can't be improved, only subtracted from.

Modest angles in each prism mean that they have to be counter-rotated more, leading to much more astigmatism and CA problems.

Large angles add to weight and space problems: the fatter the prism the heavier it is and the more room it takes up.

The optimum is around 30 degrees (total), plus or minus a little, for the smallest angle. All prism systems perform exactly the same as far a geometry is concerned, as do the simpler anamorphic cylindrical lenses, given astigmatism performance benchmarks are kept to the relatively "high quality" end of the scale. Whatever you add to one side of the equation, you take away from the other side of the equation. Prisms have only flat sides... no degrees of freedom in design. You can tweak prisms, add correctors etc., but there's a ceiling of maximum performance you can't penetrate.

You may think you've got a great picture (as do many HTB and other prism owners), but until you see a really GREAT picture coming off a well-designed cylindrical, you're fooling yourself.

**Aussie Bob**The improvement is vast. A cylindrical can be designed to do almost whatever you want, given enough curved surfaces. The more the better.

Prisms respond in one way only: no matter what angles you use in the prisms themselves, there's a performance bottom line that can't be improved, only subtracted from.

Modest angles in each prism mean that they have to be counter-rotated more, leading to much more astigmatism and CA problems.

Large angles add to weight and space problems: the fatter the prism the heavier it is and the more room it takes up.

The optimum is around 30 degrees (total), plus or minus a little, for the smallest angle. All prism systems perform exactly the same as far a geometry is concerned, as do the simpler anamorphic cylindrical lenses, given astigmatism performance benchmarks are kept to the relatively "high quality" end of the scale. Whatever you add to one side of the equation, you take away from the other side of the equation. Prisms have only flat sides... no degrees of freedom in design. You can tweak prisms, add correctors etc., but there's a ceiling of maximum performance you can't penetrate.

You may think you've got a great picture (as do many HTB and other prism owners), but until you see a really GREAT picture coming off a well-designed cylindrical, you're fooling yourself.

Fine.

How do cylindrical lens respond to variances in actual among different installations (and I take figures from your curve calculator, thanks):

1. 12ft throw, 40"inch height = Sagitta of 79mm, 30ft Curve

2. 15ft throw, 40"inch height = Sagitta of 65mm, 36ft Curve

Will the focus still be as good in both cases?