B&L Tessar F-Stop Discovery process?

[Christiaan Phleger]

Aloha all. I have recently aquired a neat little B&L Zeiss Tessar 3 1/2 x5 1/ 2 2c in barrel with no iris nor waterhouse stops. With a bit of tinkering, I discovered that the cells screw directly in to a Aphax shutter I had sitting about, and the cell spacing seems the same, and the ground glass of the Graphic displays a lovely image that I can't wait to try. However, the f-stop range of the shutter starts at 4.7 and of course goes up. With a bit of Apugging and a recent thread I've kinda determined that the starting F-stop is 6.3, I just now need to figure out the rest of them. I'm thinking of mounting the lens, putting it against a evenly lit wall, then adjusting the meter at wide open to display 6.3 (5.6 and 4/10s?) and then stopping the lens down until I hit 8 then 11 and mark the shutter. Is this a good method? Anybody have any ideas if I'm on the right track? Much thanks, and ALoha!

 

[Ole]

Is the max aperture of the lens f:6.3? And does that correspond to f:4.7 on the shutter?

Assuming I've understood you correctly, I would just assume that everything is !about a stop" offset. So f:11 on the shutter would be "about f:16". That'll be closer than the expected accuracy of the shutter speeds!

 

[Helen B]

If, with the lens focussed at infinity, you substitute a piece of card with a small central hole for a filmholder - ie the hole is under the ground glass, where the film would be - and illuminate the ground glass, you can project an image of the entrance pupil. Then you can measure its diameter with relative ease as long as the image is visible. However, as the shutter already has an f-number scale, couldn't you just renumber it? (edit - as Ole has already suggested)

How were you going to meter? Flat (cosine) incident?

Best,
Helen

 

[Christiaan Phleger]

Hmm, Ole idea seems so simple, that might just work. Helen, I was trying to avoid as much Photo-Math as possible, but I was going to place the meter cell flat and close. Since the shutter has a scale already I think I'll do the easy thing and shift the f-stops over.

 

[David A. Goldfarb]

If you are using the scale on the shutter, it may be that "wide open" on the shutter for whatever lens was in it before is not "wide open" for the new lens.

 

[phfitz]

Hi there,

If it is a B&L Tessar Ic it's f/4.5 and the scale should work as is. If it's a Tessar IIb than it's f/6.3 and 1 stop off as Ole suggested.

Have fun with it.

 

[Dan Fromm]

Um, er, ah, per the B&L catalogs conveniently posted on www.cameraeccentric.com, ain't no 3.5" x 5.5" B&L Tessar IIb. There are a couple of 3.25" x 5.5" IIbs listed, with focal lengths that differ minorly. 1906, 6 7/8". 1919, 6 11/16". 1920, 7 1/16".

Also ain't no 2c. Ic or IIb. f/4.5 or f/6.3, respectively. That's what B&L made in the Tessar line.

Any idea which you have? If you don't know the focal length with good precision, Helen's suggestion will get you close but not exact. Close is probably good enough.

Try Ole's suggestion.

And enjoy the lens. I have one of 'em (focal length around 7") and it isn't bad at all.

Cheers,

Dan

 

[Christiaan Phleger]

Two B or Not Two B....
Its a 2b, 3 1/4 x 5 1/2. Sorry, was drinking the first cuppa' as well as monitoring the Germany/Italy skirmish when I wrote that. My consensus is to shoot it one stop off and test it with some Provia, with notes, to fine tune it. Many thanks!