Someone please correct me if I'm wrong here, but the focal length on the 6x9 isn't what makes them so hot... although anything placed at the focal point 9 inches out is going to burn!
Didn't the old instruments produce more heat in the light path due to the fact that they have a metal
reflector. Meaning they reflect all the Infrared forward into the gate. The newer instruments have
dichroic glass reflectors which pass a large percentage of the I.R. into the body of the
instrument, reflecting mostly just the visible light forward into the gate. Thus they are cooler out front.
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