If your referring to a vertical versus a horizontal type lens, they really do the same thing, but in a different manner. In both situations, you first have to scale the 2.35 image (vertically stretch) to reclaim the black bars.
The horizontal lens then takes that image, leaving the height alone, and horizontally stretches it back out to fill your 2.35 screen. In my opinion, these are best if your limited on depth of your room, and trying to achieve a big screen from a shorter throw distance.
The vertical design takes the same image and compresses(squeezes) it down from top/bottom until it fills your 2.35 screen. I think most people that use these types of lens, have a longer throw type projector, I don't think they would work that good from a short distance as your end result would be a smaller screen.
Hope this answers your question.
