How very clever but simple.

Quote Originally Posted by Steven Tribe View Post
The classic T-P design involved a thin, removable, lens board in front which was fixed to a particular lens. Later, the same curtain system with speeds of up to about 1/90 sec was mounted in a more secure box design with adjustable mounts for a range of lens hood diameters. Superb system for heavy Petzvals and big aplanats. A lot of these are of no-name manufacture.

Photos show the same front shutter on the first 3 Petzvals I fished out this morning!

External hood diameters are from 9-11.5 cm.