I have a set of 68mm diameter 90mm focal length (f/1.35) semi-apochromatic lenses purchased from Paul Rini Optics (http://proptics.ieasysite.com/paul_rini_optics_002.htm, bottom of page).

While Paul is selling the set for around $30, the lenses originally cost $350.00. Being "semi-apochromatic", there will be very little lens induced color divergence and should also provide a superior flat image. Even better, with a 90mm focal length, it should be possible to construct a reasonably shallow RPTV without having to resort to an expensive first surface mirror. Before committing the resources, I wanted to see if anyone else here had experimented with such short FL, highly corrected lenses. Even if not, I thought I'd gather opinions before venturing out.

My ideas: It seems high quality, short FL lenses like this would be ideal for a medium-sized RPTV in a box (60"-72") with a smaller LCD panel (7" to 8"), or a really large hanging screen RPTV where you have maybe 3 feet behind the screen to project the image. At 90mm FL, you don't need much space to get a large image.

I thought a lens set like this would be ideal where you wanted to commit maybe 3 or 4 feet at the end of a room to the rear projector and screen and built or erected shelving to the left and right to hold your equipment.

-coma

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