Protar question

[Simon Benton]

I purchased a Compound 2 shutter for parts and with it came 2 B&L Protar VII cells of 8 3/4 and 11 3/16 inch length - both screw into the Compound. On the aperture scale on the shutter it has markings of 7 in/f7 and 6 1/8 in/f7.8 and 5 5/8 in/f7.

I doubt if these 2 lens cells are for this particular shutter/aperture scale but I would be grateful if any one can tell me if I can use these cells on their own (front or back)or in combination and what would the aperture and focal length be. Or perhaps point me to any links that would have this information. Thank you!

[benrains]

The focal length of the combined lenses would be just short of 5-in based on the simple formula for compound lenses: 1/F = 1/f1 + 1/f2 where f1=8 3/4 and f2=11 3/16, solve for 'F' to get the combined focal length.

I can't imagine any reason why you couldn't use the cells individually. I don't know if they'll be especially sharp on their own, but if they're labeled with focal lengths, they might have been intended to be used that way on a convertible lens. You'll still have to figure out the correct aperture settings (which is not prohibitively difficult, but it can be tedious.)

[benrains]

Of course, it might also be worth trolling through the old Zeiss or B&L catalogs on Camera Eccentric- http://www.cameraeccentric.com/

I just noticed that the 1927 Zeiss catalog lists a Double Protar combination on pg.10 for a 5 3/4" f/7 lens with a front lens of 11 1/2" and a rear one of 8 3/4"... which is pretty close to the 5 5/8". So you may just have an older or a newer version of the same with a slightly different focal length. I wouldn't be surprised if the 5 5/8" aperture scale works for you with the cells you have.

[benrains]

And... I'm now just noticing that there are other Double Protar combinations listed for lenses of 6" and 7 1/4" (close to the other aperture scales on your shutter) which include a 14" lens with the 8 3/4" and 11 1/2" respectively. So possibly, originally, there would have been a set of three cells--the two you have and a 14" as the third. Those three could then be mix and matched to get the three aperture scales you see on your shutter. All the cells individually have a maximum aperture of f/12.5.

[Simon Benton]

I have also noticed that the serial numbers of the 2 cells are in sequence - xxxx114 and xxxx115

[Jim Galli]

My 1912 B&L Catalog lists a C set just as you've described. The 2 elements present combine to make the 5 5/8 inch f7 set. You're missing a 13 3/4" single which combined with the 8 3/4 gives 6 1/8" f7.7, and when combined with the 11 3/16" gives 7" f7.7. A 13 3/4" single is not too hard to find but you'll need one in matching size and threads to fit the #2 Compound.

[Uli Mayer]

For making sure that your shutter has the proper aperture scales for your Protars, you could measure the actual iris diameters at some F-stops, and compare them with the diameters provided by Zeiss on its aperture tables:
http://www.geocities.com/westontina/protar/index.html

Uli

[john wilton]

Is the Compound anywhere near working? I just fixed one that had a loose shutter blade and jammed piston. If it is at all fixable it seems a shame to divorce it from the Protar cells!

[Simon Benton]

Compound shutter works very well and actual speeds are close to marked speeds. I was also lucky enough to locate a 13 3/4 in Protar cell thanks to Emil. Thank you everyone for your advice.