Just got a "new" lens today and was completely thrilled until I looked at the f-stop scale. I already searched through some books, but haven't found anything yet, so I thought I'd ask here if someone knew before I can find the right book....

Anyway, the problem is the numbers and here they are:

(wait, had to find reading glasses)

6.8 9 12.5 18 25 36 50

Now the 6.8 is correct for this lens in standard f-stop. After that, I don't know? The 25-36-50 seem to be maybe the old system (which I can't find in a book right now...), but I thought 50 would have been a fairly low-open stop compared to the at least f-45 it should be on this shutter? Maybe it's really f-50 in the current system? I doubt it...

This is an _old_ CP Goerz Compur dial set shutter by the way, and aparently not for export as the decimal seperator is a comma and not a peroid. So it's apparently a home-toen German shutter...

Okay, did a lot of searching.

It's NOT the old American system, or even the old Goerz system...

So, I measured the exit pupil, divided into the focal length... Turns out they are the real f-stops.... Who ever hear of f-50?

I suppose I'll be doing a lot of guessing whenever I use this lens

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On 2005-03-10 11:08, RichS wrote: Just got a "new" lens today and was completely thrilled until I looked at the f-stop scale. I already searched through some books, but haven't found anything yet, so I thought I'd ask here if someone knew before I can find the right book.... Anyway, the problem is the numbers and here they are: (wait, had to find reading glasses) 6.8 9 12.5 18 25 36 50 Now the 6.8 is correct for this lens in standard f-stop. After that, I don't know? The 25-36-50 seem to be maybe the old system (which I can't find in a book right now...), but I thought 50 would have been a fairly low-open stop compared to the at least f-45 it should be on this shutter? Maybe it's really f-50 in the current system? I doubt it... This is an _old_ CP Goerz Compur dial set shutter by the way, and aparently not for export as the decimal seperator is a comma and not a peroid. So it's apparently a home-toen German shutter...

They are at one stop intervals, starting from f/6.8, which is one half stop below f/5.6.

Quite a few prewar German lenses (and American ones made under license) use that aperture sequence. I have several "Protars" of various ages; the extra-wide ones have a maximum aperture of f:18, the others, of f:12.5.

BTW, the next full stop wider than f:6.8 under this system is f:4.5...

...should have said, "f:4.5, f:6.3, f:9..." I don't think f:6.8 is linear within this system, but maximum apertures often are not.

Starnge... Don't think I've ever run into this before? Who ever knew there were stops between

So I just have to figure between these stops, or make a new dial for my meter

Gotta give 'em credit though. After measuring the stops, I measured the speeds... Right on! Not bad. The lens is pre 1918 according to the serial number and I'd bet the shutter is original to it. Bet it outlasts me (which may not be saying much )

Thanks for all the info!

I once had a Schneider "Xenar" 135mm. f:4.5 lens in an old "Prontor" self-cocking shutter with its entire aperture scale in that system: f:4.5, f:6.3, f:9, f:12.5 (sometimes "f:12.7"), f:18 and so forth.

I also have seen a B&L "Velostigmat" 180mm. f:4.5 lens in dial-set "Compur" shutter with an f:6.3 index between f:5.6 and f:8, but no further deviation from the usual Anglo-American scale.

Many light meters have two ticks (one-third stops) intermediate between the marked focal ratios. I think splitting the difference between them would put you well into the pickle-barrel in terms of exposure.

I'm sure this system was common at some point. And I guess I've just been lucky to get my old lenses with newer system scales.

You're right about the ticks between stops. Unfortunately, between work and an old truck that doesn't want to work, I haven't had the time to figure out where these stops fall. I'm sure I've seen a chart that had all the stops listed once? But I suppose between 8 & 11, there must be a '9' (what about 10??)

Maybe from a collector's viewpoint, this adds to the len's value? Like I'll ever sell anything...

And now I have to find out if it really does cover 8x10. If not, it may well be the first thing I wind up selling

<font size=-1>[ This Message was edited by: 45PSS on 2005-12-24 21:54 ]</font>

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On 2005-03-10 18:50, 45PSS wrote: When you hear it as 8&1/3 (f9);11&1/3(f12.5); 16&1/3 (f18);22&1/3 (f25); f32&1/3 (f36); and last but not least f45&1/3 (f50) its not so strange. The caculator at 8,16,32 fraction is .33something while f11,22,45 it is .289 something but close enough to state as a fraction for pratical purposes. If you do not have Fcalc you(anyone) should. http://www.tangentsoft.net/ _________________ While a picture may be worth a thousand words, a quality photograph is worth a million. <font size=-1>[ This Message was edited by: 45PSS on 2005-03-10 18:52 ]</font>

Ya see... _That's_ why I have so much trouble with my brain... I never have to use it!

Thanks... If I could just get a minute to sit here and think about it, the 1/3 stop over makes a lot of sense. There's a lot of room from 16 to 22 and 18 just doesn't quite make it half way there...

Between the tiny numbers on the shutter, being worn with age (including my eyes) and having to remember that these stops are 1/3 over 'standard' stops, this lens should be a lot of fun to use!

And oddly enough, I do have fCalc somewhere around here. I never seem to remember it though... Great program...

And now that I have 5 minutes to do nothing, it's all figured out for me, luckily

And in case anyone was wondering, it's a 21cm Dagor, and it does cover 8x10, but not much more...
Now I have to run again.....

<font size=-1>[ This Message was edited by: 45PSS on 2005-12-24 21:54 ]</font>

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On 2005-03-11 18:51, 45PSS wrote: If you don't like it you can always give it to me.

No problem, just send me your address

I'll admit that there is no sense behind this whole deal.

It all started with my fascination (obsession) with the 8x10 Century Universal. A long road of searching for info about the camera led me to Berenice Abbot and the fantastic "Changing New York" book shot in the 30's. She used a Century Universal, and of course, Dagor lenses. So I was no longer happy with my T&R's, I had to have at least one Dagor to go with the camera... I ran across a beautiful 12 inch a few weeks ago at a 'fair' price that I couldn't resist. Then I just found this 21cm at what I thought was a great price, plus the focal lengths all complemented each other... Now I'm happy, and I'm sorry to say that neither the Century Universal nor the Dagors will ever leave my posession, voluntarily anyway... And there's the whole boring story...

In the 30s there were two f-number systems competing. The Continental System and the English System.

Goerz, being on the continent, went with that system.

Kodak and a few others, not being on the (right) continent, went with the English system and won.
and Dan is right, f6.8 is not a whole stop, f6.3 is.

This according to The Handbook of Photography.

Thanks for the info Les.

Gees, you'd think these lens designers would at least design their lenses to be at a full stop when wide open. Sure can't be that hard

Luckily, my other Goerz is from approx 1935 and has the current f-stop scale. I guessing that shutter is original also...

The fun and learning never end. But it must have been a whole lot more fun back then before the "standards", between f-stops, film speeds, bulb ratings, etc... How did they ever make photographs?

There were actually more than two f stop systems. If you can get your hands on a copy of Graphic Graflex Photography, 1947 edition, in there somewhere is a table that gives the relationship between the different systems. If I get time, I'll look for it in my copy. For all practical purposes, if you use f:18 as 16, then progress either way from there using modern equivelents, you will be just fine.