PDA

View Full Version : Bausch & Lomb 12” E.F aperture

Jfnphotography
10-Jun-2010, 05:02
I picked up a Bausch & Lomb 12” E.F Projection lens.

Is 12” the Focal Length of the lens?

To fine the aperture you divide the focal length in inches by the diameter of the lens in inches?

So if the lens focal length 12” and the diameter is 1.929” then the aperture would be 6.22 wide open?

I want to put a Synchro Compur shutter in front of the lens. If my shutter highest fstop is f3.8 will that now become F6.22 and I can calculate the rest of the fstop from there?

eddie
10-Jun-2010, 10:44
yes, you are thinking of this correctly. it may be easier (math wise) to use mm. it is for me

cowanw
10-Jun-2010, 11:11
Assuming the shutter opens to 2 inches.
Regards
Bill

ic-racer
10-Jun-2010, 15:12
diameter of the lens in inches?

Actually you want to observe and measure the entrance pupil. The optics may make the aperture appear bigger or smaller than it really is.

Jfnphotography
10-Jun-2010, 18:29
"observe and measure the entrance pupil"
Is that were you shining a light threw the lens then measure the image circle that it makes. Read something about that. I think you put the light 15 inches from the center of the lens. Might try it, if the fstop is way off. Still working on mounting the shutter. Hope to test the lens soon.

Jfnphotography
10-Jun-2010, 18:43
Just did a test at 15" the lens make a circle that is 8" wide. For me to cover my 4x5 film I need to be 12" from front of lens to the film.

eddie
10-Jun-2010, 22:21
to focus at infinity you need to be 12 inches from film to "slot"

a 12 inch lens will easily cover 4x5

Jim Galli
10-Jun-2010, 22:45
Most of the ones that say 12" EF are triplets. Your shutter will be the limiter unless you've got a really big shutter. ie. if your shutter max opening was 40mm you would divide that into 305 (12") and come up with f7.6 A Packard shutter (http://tonopahpictures.0catch.com/Article_About_Packard_Shutters.html) is your friend. Find a 5" Packard with 2 3/4" openings and cobble it to the front of the lens with a 2" tape core or a piece of ABS pipe cut to size. Glue it all together and go to town. Packards can also be synced for flash fairly simply.

Jfnphotography
18-Jun-2010, 12:40
Here is the first photograph with the 12" B&L lens with the Synchro Compur shutter in front of the lens. I used F8 as my wide open stop. This is with polaroid 672 film 400ASA expired in 2006. All natural light bounced into photograph. Behind her about 5ft away was a large plant and brick wall. Going to test outside next with some film.