Couple of quick questions/clairifications that I haven't been able to solve myself.
Is a longer focal lengh on the fresnels better? Ie 220mm vs 660mm.
The "front" fresnel is between the lcd and the lens, correct?
Should the front fresnel have a longer focal length then the back fresnel (between the lcd and light point)? If so, what is the rule of thumb? 1.1x the back fresnel? I saw someone doing a 220mm back with a 550m front, so I'm not exactly sure what focal length would be best.
Finally, should the focal length of the front fresnel match the focal length of the lens?
The more I dig into this stuff, the less I seem to know....
Is a longer focal lengh on the fresnels better? Ie 220mm vs 660mm.
The "front" fresnel is between the lcd and the lens, correct?
Should the front fresnel have a longer focal length then the back fresnel (between the lcd and light point)? If so, what is the rule of thumb? 1.1x the back fresnel? I saw someone doing a 220mm back with a 550m front, so I'm not exactly sure what focal length would be best.
Finally, should the focal length of the front fresnel match the focal length of the lens?
The more I dig into this stuff, the less I seem to know....
Not necessarily. You want a fresnel with a focal length that matches your needs. You'll have to check your calculations to find out which focal length (FL) is right for you.
Yes. Front, field, objective (I think) are all names for the fresnel that is between the LCD and the projection lens (in a split config).
Nope, doesn't matter. People use 220mm FL in the back because the light that hits the LCD is more intense (due to the bulb being closer to the LCD). The front / field fresnel is determined by the throw, projection lens focal length, LCD to projection lens distance and whether or not you have a split or unsplit config.
Not necessarily. In fact, most often not. I have a 457mm FL projection lens and a 550mm FL field/front fresnel lens. This question has been asked before.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=72244&highlight=
Don't worry. Once you understand what's going on, it's all pretty simple.
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