Constant Image Height Projection - No Zooming

Having replaced my trusty old Sony 1271QM CRT projector with a shiny new JVC X500R digital model, I wanted to display a range of movie formats on my 139" Seymour AT based DIY 2.35:1 aspect screen with minimum of fuss.

Typically, this is achieved either by using a costly and cumbersome anamorphic lens or by setting up lens memories on the projector which are recalled manually based on the input resolution.