Prewar Lens f-stops

naql

naql

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I recently got a prewar FED NKVD with its original lens from FEDKA and I noticed the lens has the old style aperture numbers on it (3.5, 4.5, 6.3, 9, 12.5, and 18.) Does anyone know how these match up to the modern f numbers? Idid a google search and it pulled up a chart from 1899 and that wouldn't seem to fit with the newer system.

Thanks!
 
See the attached table.

Meaning f3.5 is about half stop (56%) slower than f2.8, f4.5 about a quarter (27%) slower than f4, etc.

Hope this helps,

Roland.
 
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It's not really different from the modern system at all. It's just that a different set of points on the same scale is marked. You still get twice / half the amount of light from one stop to the next. (Factor of sqrt 2 = 1.41 between numbers.)

Simply meter for the stops you have, or if you prefer, eyeball your 4 - 5.6 - 8 - 11 - 16. (I assume there are no click stops on this lens.)
 
Thanks guys that all makes sense. I didn't know that they had marked off different f stops on the scale than they do now.

I can't wait to see what I get out of this lens. I've never had the opportunity to try out an uncoated lens before.
 
Gee, I just looked at Fedka's write-up of this type -- a sobering story BTW -- and aren't you going to have "fun" with that speed series. 20 - 30 - 40 - 60 - 100 - 200 - 500? If there's any logic to that, it's lost on me.

I guess I'd forget about the 1/40 and hope that, in the real world, the others are near enough half from one to the next.
 
Stephen S. Mack said:
They DO take a little getting used to, but the cameras and lenses kind of grow on you, don't ya know?:cool:

With best regards.

Stephen
Click to expand...

Yeah it is a lot different from what I'm used to. It took me almost an hour to load my first roll of film. I guess I should've looked up the instructions first.

I was kind of disappointed to read that the lens is pretty much married to the camera because of the 28.5mm back focus instead of the 28.8 on post war FSU cameras and lenses.
 
naql said:
I was kind of disappointed to read that the lens is pretty much married to the camera because of the 28.5mm back focus instead of the 28.8 on post war FSU cameras and lenses.
Click to expand...

That's what you get for buying prewar. You can either hunt down the corresponding prewar lenses now, or get a FED-S or a postwar Zorki 1d or something - it basically handles the same, except that it uses the standard lens thread.
 
1/3 stop different in most cases.

f/2 - f/2.2, f/2.8 - f/3.2, f/4 - f/4.5, f/5.6 - f/6.3, f/8 - f/9, f/11 - f/12.5, f/16 - f/18

f/3.5 is out of sequence, 1/3 stop faster than f/4, 2/3 stop slower than f/2.8, just to give a 'fast' maximum aperture (it was in the 1930s).

Speeds are easy enough too, again in 1/3 stop steps:

1/4 (1/5, 1/6) 1/8 (1/10, 1/12) 1/15 (1/20, 1/25) 1/30 (1/40, 1/50) 1/60 (1/80, 1/100) 1/125 (1/160, 1/200) 1/250. Obviously there's a certain amount of rounding.

Additional slow speeds were offered mostly because they could, but also because at long hand-held speeds with slow films, even 1/3 stop is often worth having, let alone 2/3 stop.

Cheers,

R.
 
Roger Hicks said:
...
f/3.5 is out of sequence, 1/3 stop faster than f/4, 2/3 stop slower than f/2.8, just to give a 'fast' maximum aperture (it was in the 1930s). ...
Click to expand...

Just as lenses are marked today. The maximum aperture is frequently "out of sequence" with the conventionally marked apertures (e.g. f/1.8 which is 1/3 stop faster than the "conventionally marked" f/2.0).

There was an older aperture numbering system sometimes seen on old Kodak cameras and a few other American models. This was called the "uniform system" and doubling the number resulted in half the exposure. It wasn't very popular.
 
batterytypehah! said:
... and aren't you going to have "fun" with that speed series. 20 - 30 - 40 - 60 - 100 - 200 - 500? If there's any logic to that, it's lost on me.

I guess I'd forget about the 1/40 and hope that, in the real world, the others are near enough half from one to the next...
Click to expand...

I've taken apart and serviced several types of old shutters, both leaf and focal plane. Pretty amazing stuff. Once you see how they work, you realize that (on the best of days) the performance varies from wishful thinking to ingenious rough approximations. Letting film latitude cover the difference between one stop this way or that helps me enjoy the clicking and whirring sounds when I push the little button.
 
Proteus617 said:
I've taken apart and serviced several types of old shutters, both leaf and focal plane. Pretty amazing stuff. Once you see how they work, you realize that (on the best of days) the performance varies from wishful thinking to ingenious rough approximations. Letting film latitude cover the difference between one stop this way or that helps me enjoy the clicking and whirring sounds when I push the little button.
Click to expand...

You are quite right. We are not dealing with precision technology. That's why you don't need to worry about the difference between GOST and ASA or fret about finding a distant target to calibrate a rangefinder ( a couple of hundred yards is fine).
 
Roger Hicks said:
1/3 stop different in most cases.

f/2 - f/2.2, f/2.8 - f/3.2, f/4 - f/4.5, f/5.6 - f/6.3, f/8 - f/9, f/11 - f/12.5, f/16 - f/18

f/3.5 is out of sequence, 1/3 stop faster than f/4, 2/3 stop slower than f/2.8, just to give a 'fast' maximum aperture (it was in the 1930s).

Speeds are easy enough too, again in 1/3 stop steps:

1/4 (1/5, 1/6) 1/8 (1/10, 1/12) 1/15 (1/20, 1/25) 1/30 (1/40, 1/50) 1/60 (1/80, 1/100) 1/125 (1/160, 1/200) 1/250. Obviously there's a certain amount of rounding.

Additional slow speeds were offered mostly because they could, but also because at long hand-held speeds with slow films, even 1/3 stop is often worth having, let alone 2/3 stop.

Cheers,

R.
Click to expand...

Roger,

Stops are a logarithmic progression if I remember right, no?

B2 (;->
 
BillBingham2 said:
Roger,

Stops are a logarithmic progression if I remember right, no?

B2 (;->
Click to expand...

Dear Bill,

No. Square root of 2 (1.414 recurring) because stop diameter is linear and the area of the hole that the light gets through varies as the square of the linear dimension. Thus f/2 - f/4 - f/8 - f/16 each cut the light to 1/4 of its previous quantity, necessitating f/2.8 - f/5.6 - f/11 as intermediate values to halve them between the 2-4-8-16.

Cheers,

R.
 
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