Custom Lens or mirror system for converting 4:3 to 8:3?

[futnuh]

Okay, bizarre question of the day ... I've got a 1400x1050 DLP with 4:3 aspect ratio. I'm looking for a means of splitting the image into two equal horizontal bands and displaying these side by side. That is, I want to place the top 1400x525 pixels side-by-side with the bottom 1400x525 pixels. (Ideally a 15% overlap for blending.)

Why? Our target rear projection screen is 2m x 0.375m or 8:3 aspect ratio. Rather than double up on projectors, I wondered about a lens/mirror/prism system for the job. For a mirror solution (placed somewhere between the lens and the image plane), it would undoubtedly be necessary to throw away a few tens of rows of pixels from the bottom of the top-band and top of the bottom band.

Thoughts? Is this just plain crazy or, conversely, are there already commercial solutions available?

[cyberheater]

There is nothing available off the shelf that will do that. You'd have to have something custom made which would probably work out more expensive then getting another projector.

[Penfold73]

Doesn't 2m x 0.375m = 16:3?

You can make custom anamorphic lenses youself to stretch your 4:3 aspect ratio projector image horizontally or to compress it vertically. Then you scale the input accordingly so that the result looks correct. Probably a lot easier than splitting and recombining as mentioned above. Worth a try?

[Gary Lightfoot]

A simple anamorphic lens will convert your 4:3 pj to a 16:9 pj, or if you use just the 16:9 portion of your display (1400 x 788), you can use the lens to give you a 2.35:1 display,

Gary

[cyberheater]

Gary and Penfold. Reread what that guys trying to do. It's not a simple anamorphic squeeze.

[Penfold73]

Couldn't the result he wants also be achieved this way though?

And 2m x 0.35m is 16:3 not 8:3, is that really the aspect ratio he wants?

[Gary Lightfoot]

I know what he's trying to do, but it seems a lot simpler to use an anamorphic lens to get 2.35:1 than splitting the image and lay it side by side to get 2.6:1. With blending the image will be smaller than 2.6 and closer to 2.35:1 anyway.

Gary

[cyberheater]

Oh I see. You guys did get it.

It sounds to me that the horizontal resolution is important to him which is why he's trying to do it this way.

[Gary Lightfoot]

There are anamorphic lenses that will stretch 4:3 to 2.35:1 (X 1.75) and 2.6:1 (X 2) that will allow full use of the pjs resolution, but they tend to be for movie theaters with much longer throws, and those that are for 16mm (usually used in the home) tend to have orifices which are too small for the beam a digital pj gives out IIRC.

Ebay night be worth a look but you really need to know what the physical dimensions are of the lens as well as it's magnification.

Just thought John - you had a 16mm anamorphic lense once didn't you? It was too small to get good results with or something?

Gary

[cyberheater]

Gary. My small anamorphic was too small for useful results. Too much vignetting.

It sounds to me he would have to use a set of mirror to split the picture in the middle and then somehow build a couple of periscopes to align the images side by side.
I seriously doubt that you'd get good alignment with that arrangement. And you'd have to use first surface mirrors which aren't cheap.