View Full Version : strange fstops ... do i use them, or an equivalency

25-Apr-2004, 12:25

i recently acquired a protar lens, but the fstops aren't like the ones i am used to.

18 - 24 - 36 - 50 does this lens use a different system altogether, or are these just in between 16 - 22 - 32 - 64 :)

thanks! john

Dan Fromm
25-Apr-2004, 12:46
if it is a protar v, max aperture f/18, the numbers you see are just inbetween.

25-Apr-2004, 12:57
thanks dan!

not sure if it is a protar v. - the lens only says f-14cm, 1:18 i had a feeling they were just inbetween, but wanted to make sure. i at one point had a tiny little 58mm brass lens and the markings were in the stoltz system .. took me a while to figure that one out :) ... this one seems to be a no brainer ( now at least! )


Jason Greenberg Motamedi
25-Apr-2004, 13:12
Hi John! Funny meeting you here...

I had what I think to be the identical lens, a 14 cm f18 Protar, which also had the same markings on barrel: After some measuring and calculating I came to the conclusion that these are indeed in the "in-between" f/stops. These wide angle protars are pretty amazing lenses...

Jason Greenberg Motamedi
25-Apr-2004, 13:17
I should also say that my Protar had a little brass strip inside the barrel which, when removed, allowed the iris to open slightly wider (~f/13 or so). This made composition easier. However, be sure to focus at f/18, since there is a danger of focus shift.

25-Apr-2004, 13:17
hi jason :)

i have heard great things about this piece of old german glass and can't wait to use it !

thanks for the reassurance :)

- john

Ernest Purdum
25-Apr-2004, 13:49
Your lens is marked in the "Continental" series. It is indeed in between the modern series. Some of the other markings in the Continental series are f4.5 and f6.3, which explains why so many lenses have these as their maximum apertures.

Your 14cm lens was rated to cover 6 1/2" X 8 1/2" wide open. This would give useful movements on 5" x 7" and a lot of movement capability on 4" X 5". If using it on 4" X 5", careful lens shading would be important to avoid loss of contrast and possible flare.

Ole Tjugen
26-Apr-2004, 20:05
The German Wide-angle Protar f:18's carried no "series" designation, but were marked only with the focal length (in cm) and the maker. Yours is a Carl Zeiss Jens (Nr. #Serial Number#) Protar 1:18 f=14cm?

The marked stops (18-25-36-50) are correct. Although I wasn't aware of any "Continental" system, it fits in nicely with the majority of German lenses of that age. So a more complete (as on my very old Xenar) series would be 4.5-6.3-9-12-18-25-36-50. It's easier to think of it as one third stop offset from what we're used to, so that f:18 corresponds to f:16 and a third.

According to my contemporary literature (1910), the Protar 1:18 will cover three times the focal length. That gives this little gem an image circle of 420mm, which is more than sufficient for 8x10"! Light fall-off follows cos^4, which loses 3 1/2 stops at the edge of that circle.