I was reading through this forum last night and I stumbled upson some box designs that used a different fresnal lense setup. It seems they have both the lenses before the LCD, in what is refered to as the OHP style. Can someone explain this a ltitle to me ? I read it is supposed to produce a sharper picture at the cost of no keystone adjustment. Is this true ?

Thanks,
Tim

At the cost of no keystone adjustment and a very sharp dropoff in light output at the edges.

The amount of light that passes through an LCD is (unlike an overhead transparency) proportional to its collimation (how parallel the rays are). With both fresnels before the LCD, the light at the center gets fully transmitted, while the light at the edges gets mostly blocked by the LCD, since it's at a big angle.