Focus issues with DIY prisms | Thread profile

Hi all, So I took delivery of 2 trophy prisms from Crystal Factory a couple of weeks ago. I took the ptae1000u off the ceiling and set it up on a table the same distance as my ceiling mount and projected it on my 2.37 BOC screen. I put the prisms in front of the lens and fooled with it for about an hour or so. It really was quite a simple process to get the stretch correct. The problem ...

A couple of things to consider - These prisms are trophies and were never intended to be used as a optical component. Granted they are smooth and appear flawless to the eye and may even be finished to a "comercial optical grade", but they are far from the true optical correctness needed for a lens. Your projector's smoothscreen is by default a softening filter, and the displaced prisms ...

Thanks for your reply Mark. I didn't expect perfection from these prisms, but I dont hear anyone talking about major focus shifts when using them, so I thought I was doing something wrong. It is likely as you say, the stretch is accentuating the smoothscreen. When trying to focus a stretched image I can get vertical lines (on a focus chart) close, but any horizontal lines are brutal. ...

Quote: Originally Posted by darryldh Thanks for your reply Mark. I didn't expect perfection from these prisms, but I dont hear anyone talking about major focus shifts when using them, so I thought I was doing something wrong. The concept works and it is quite an experience to project Scope the way it was meant to...

Quote: Originally Posted by CAVX Not to sound negative, but there is way more to good optics... Agreed. But even back in the day when you guys first discovered these prisms, I never read anything that would make me pause because of comments about debilitating focus. I guess I will test on the cheap lcd, just...

Quote: Originally Posted by darryldh I guess I will test on the cheap lcd, just for kicks, but the reality is I have a decision to make. Live with the poor focus (in live action, it isnt as noticable as on the focus chart) or go back to zooming. Thanks for your help Mark Darryl Not a hard one though Darryl...

Quote: Originally Posted by CAVX Not a hard one though Darryl. Use the full panel or throw away 25% of the vertical rez? I'll take the softened image thanks Mark I can't believe CAVX is serious about that last statement. What he is saying is that even though sticking two pieces of trophy glass in front...

Quote: Originally Posted by taffman I can't believe CAVX is serious about that last statement. taffman, given Marks history and contribution to this subject, I chose to drop the subject (and the prisms) rather than push any buttons, but he was right about one thing though... the decision was easy. Darryl

Two raw prisms will never focus a converging beam in both horizontal and vertical directions. You may as well give up, as it'll never happen. You can have one or the other perfectly sharp, but not both. You have to settle on a compromise focus in between ideals for both. And then you'll notice that your "best" focus is only "best" for one area on the screen. This didn't really become ...

Quote: Originally Posted by darryldh Thanks for your reply Mark. I didn't expect perfection from these prisms, but I dont hear anyone talking about major focus shifts when using them, so I thought I was doing something wrong. It is likely as you say, the stretch is accentuating the smoothscreen. When trying to focus a ...