Originally Posted by archiguy
I remember some guys used to stack those Sony G-90 CRT projectors to double the light output. I think I recall one guy who did it on the Forum (Art?) had some big-shot calibrator there for a week
getting those two titanic tanks with six 9 inch guns perfectly aligned.
There's a big difference between CRTs and Digital Projectors, with a CRT you can (and I'm going to kill the terminology here) adjust the guns/geometry such that you can get two machines perfectly aligned. You can push/pull a portion of the frame (corner, side, etc) essentially independently of each other. This is necessary since no two machine have exactly the same optics/construction/alignment.
With a digital projector you don't have that option, the overall geometry of the output is fixed, you can zoom/shift the image, but it's all proportional across the picture. That means you need to resort to electronics, like here: