Hi Bruce,

For the record :
re : light beams, I never said that the doors break the beam! You set up the beams parallel with the edge of the door & about 10cm in front of it. The trick is to offset the 2 beams to the interior, but by different amounts, & on L-shaped brackets. If you get this right, the beams will move past each other, without any interference, just before the doors close.
In any case, anyone stupid enough to be 60 feet up in the top of the observatory (did you check out the web-site yet?) leaning out that door when it closes, deserves to lose an appendage;-)

Regards,

Richard