View Full Version : Aperture Scale Measurements for a Bausch & Lomb 3A (B&L copy of the Dallmeyer 3A)

Jay Decker
30-Nov-2011, 21:59
Does anyone have the aperture scale measurements for Bausch & Lomb 3A (B&L copy of the Dallmeyer 3A)? The f/ stop marks on the copy I have are worn off. All I need are the measurements so I know where the stops should be.



Steven Tribe
1-Dec-2011, 03:15
If the two screws holding the aperture indication plate are easily turned, if might be a good idea to remove it and acid etch the numbers and marks so the problem doesn't come up again in 50 years!
I am sure expertise about wax protection and acid is available here!

1-Dec-2011, 05:25
Nice looking lens. Why don't you reverse engineer your own marking spots? I've seldom seen one of these B&L Petzvals with this type of iris adjustments, so I doubt you'll find a match. But you can just divide the focal length by your apparent entrance (aperture seen from the front) width to get the F value at that setting. Fiddle with it to get the standard F range, and you'll have your marks.

1-Dec-2011, 06:26
measure it wide open then divide by the square root of 2. then adjust your aperture to that diameter opening and mark the scale.

etc etc.