Steve, I have a 2-3/4" diameter hole in the box with a piece of glass held into place using 3M marine silicone. The camera lens extends to within 1/8" of the glass - it's very close. You can get this box at Home Depot in the electrical section. They are 6x6x6 and waterproof. If you drill a hole smack in the bottom center that will take a 1/4-20 bolt to hold the camera. For some lucky reason it works out just right. The camera sits on a 5/8" piece of wood to bring it up a bit inside the box.
Hmm, I edited this to say that I don't know the actual distance. I thought at first you want to make a box to hold the camera but I think you just want the distance. You can just turn on the camera and let the lens extend and then measure back from the lens to the mounting hole on the bottom of the camera and then add say 1/4" to have clearance to your window.
-Mike
Last edited by Mike_M; 10/13/09 12:25 PM. Reason: I don't think I answered your question.