Question about Lenses and focal lengths... in German

[Renger-Patzsch Scholar]

Hello, Friends—

I've posted a few questions in other subforums related to a book project I'm working on about the writings on photography of the early-20th century German photographer Albert Renger-Patzsch. This community has been an extremely valuable resource as I delve into some of the minutiae of early-20th century photographic technology. My latest query involves a German sentence I'm trying to decipher that demands that I have more knowledge about focal lengths and apertures than I in fact possess. Consequently, any assistance that anyone can offer will be greatly appreciated. I'm mainly looking for the correct technical vocabulary so that I can translate a sentence correctly.

Here's the context: I'm translating an essay and at one point, Renger-Patzsch addresses advances in lens technology in the late 1920s/early 1930s. In German, he writes: “Das Objektiv, als eins der wichtigsten fotografischen Hilfsmittel, ist zu grosser Vollkommenheit entwickelt worden. Es sind Lichtstärken erreicht worden von F : 1,5 und darunter, d.h. die freie Oeffnung verhält sich zur Brennweite wie 2 : 3 und nähert den maximalen Wert.” I’ve translated this sentence thusly: “As one of the most important photographic tools, the lens has been developed to a state approaching perfection. Speeds have been attained of f/1.5 and faster, that is, the free aperture relates to the focal length at 2:3 and approaches the maximal value.” But what I'm a bit confused about are 1) the term "free aperture" (freie Öeffnung) and 2) the verb "verhält sich zur Brennweite wie 2:3." What exactly would it mean to be connected to or be related to a focal length at a ratio of 2:3 (and is "be related to" or "connect to" even the right word for this?)

So again, thanks in advance—any insight anyone can offer will be greatly appreciated.

[reddesert]

He's just saying that f/1.5 means the aperture diameter is 2/3 of the focal length. It's a restatement of the definition of f-number. You could translate it as "the aperture is in a ratio of 2:3 to the focal length." The maximal value is presumably an allusion to the idea that the theoretical fastest f-number of an ordinary lens is f/0.7 (and there have only ever been a few usable lenses for photography that were f/1 or faster).

[Dan Fromm]

He's just saying that f/1.5 means the aperture diameter is 2/3 of the focal length. It's a restatement of the definition of f-number. You could translate it as "the aperture is in a ratio of 2:3 to the focal length." The maximal value is presumably an allusion to the idea that the theoretical fastest f-number of an ordinary lens is f/0.7 (and there have only ever been a few usable lenses for photography that were f/1 or faster).

f/0.5 in air, red. Oil immersion objectives can be faster.

[Renger-Patzsch Scholar]

Aha! Thank you for this. Very helpful indeed. You guys always come through with these.

[Nodda Duma]

Pardon if I nerd out on the topic a bit.

Dan, the 0.5 (in air) limit for f/#can be misleading, as the 1/2NA = f/# is a small angle approximation so it doesn’t truly indicate what the lens is doing. If you use the exact definition for Numerical Aperture and work back from an f/# of 0.5 (maximum possible), then you find the maximum effective f/# is 1/sqrt(2) ~ 0.7071. This is what reddessert is referring to. In reality, the effective or working f/# determines the light collected on the image side and is what counts.

I got to play with these nuances earlier this year, when I had to design an f/0.7 optic to get an effective ~f/0.86 lens. Personally I find it’s easier to think in terms of numerical aperture at fast f/#’s.

[Havoc]

Here's the context: I'm translating an essay and at one point, Renger-Patzsch addresses advances in lens technology in the late 1920s/early 1930s. In German, he writes: “Das Objektiv, als eins der wichtigsten fotografischen Hilfsmittel, ist zu grosser Vollkommenheit entwickelt worden. Es sind Lichtstärken erreicht worden von F : 1,5 und darunter, d.h. die freie Oeffnung verhält sich zur Brennweite wie 2 : 3 und nähert den maximalen Wert.” I’ve translated this sentence thusly: “As one of the most important photographic tools, the lens has been developed to a state approaching perfection. Speeds have been attained of f/1.5 and faster, that is, the free aperture relates to the focal length at 2:3 and approaches the maximal value.” But what I'm a bit confused about are 1) the term "free aperture" (freie Öeffnung) and 2) the verb "verhält sich zur Brennweite wie 2:3." What exactly would it mean to be connected to or be related to a focal length at a ratio of 2:3 (and is "be related to" or "connect to" even the right word for this?)

So again, thanks in advance—any insight anyone can offer will be greatly appreciated.

"freier Öffnung" is the "free opening", that which is free to pass light. So apperture is correct I'd say.

"verhält" in this case is as in a mathematical "ratio/proportion of 2 to 3".

[Renger-Patzsch Scholar]

Thank you all, this is really helpful. Greatly appreciated!

[Doremus Scudder]

Here's my translation of the sentence.

"The lens, one of the most important photographic tools, has been developed to a state approaching perfection. (this is your translations; it's perfect.) Speeds of f/1.5 and faster have been achieved, which means the ratio of aperture to focal length is at 2:3 and approaching the maximum value." (This last bit a little different than yours.)

Hope this helps,

Doremus

[Renger-Patzsch Scholar]

Here's my translation of the sentence.

"The lens, one of the most important photographic tools, has been developed to a state approaching perfection. (this is your translations; it's perfect.) Speeds of f/1.5 and faster have been achieved, which means the ratio of aperture to focal length is at 2:3 and approaching the maximum value." (This last bit a little different than yours.)

Hope this helps,

Doremus


Super helpful, absolutely. With this thread, I’ve gone from a state of absolute confusion with my hands up in the air to a point where I completely get what’s going on. Thanks to everyone for your help. This forum never disappoints.