Baush and Lomb Newbie help

[Tim Layton]

Hi, I just picked up a 12" and a 10" Baush and Lomb barrel lenses which I think are projection style lenses. Both can mount in a barrel that I have and are in good working order. I've tested the 12" on my 8x10 and the 10" on my 5x7 and all seems okay.

I am just trying to learn more about what I have exactly. The vintage lenses are a new thing for me so I am sure I am not even describing them correctly. I was told they are Triplets, but I am not sure what that means or how to tell if they are in fact Triplets or not. Any help and pointers in the right direction would be appreciated. To determine the f/stop I just divided the length by the diameter and used that as a starting place.

Thanks,

Tim

[Mark Sawyer]

Hi, Tim ~

The lenses are almost certainly triplets; only the very early B&L projection lenses were Petzval designs. The Cooke Triplet is an 1893 design that used three elements in the system, a Plano-Convex at either end and a bi-concave in the middle. You can probably identify it for sure by shining a flashlight through it and counting the reflections or the lens edges to determine the number of elements.

Determine the focal length by measuring the distance from where the lens focuses an image to just behind the middle of the lens, and divide that by the diameter of the opening measured across the front of the lens. That will be approximate but close enough to figure exposures accurately.

The Cooke Triplet is a nice design, and copies were made by quite a few companies, including B&L. Shoot some film and see what they do!

[Tim Layton]

Mark, thank you for the information. I appreciate it. I shot some paper negatives today with the 12" and really liked the results so far. Based on my initial test I ended up metering at f/5.6 and that produced a good negative. I will review the lenses a lot closer now that I have more information and see what I can come up with.

Thanks