There are Horizontal and Vertical Stretch lens designs. Mine is a Horizontal design, so first my theatetek software vertically stretches the 2.35 image to get rid of the black bars, then I turn my knobs on the lens which horizontally reformats the image to fill the 2.35 screen. The nice thing about a Horizontal design is that you can get a pretty big image from a relatively shorter throw distance.
A vertical lens actualy squeezes the image down to form the same 2.35 image but the end result is a smaller size from the same throw distance. Most people with vertical lens have longer throw projectors.
