Advice re: circa 1937 European camera aperture markings please

[jmccl@yahoo.com]

Hello all. I am acquiring a circa 1937 French manufactured 6X9 folder. Shutter speeds are 100, 50, 25, B, T. Aperture markings are 25 18 12,5 9 and 6,3. It is a 105mm lens. I am acustomed to the more traditional - - - 5.6, 8, 11, 16, 22 - - - aperture markings that I have on my Zeiss 105mm 6X9. Does anybody have any insight into this different scale on the French 1937 model vs the 1951 Zeiss? I plan to shoot using sunny 16 conventions so I imagine I will just interpolate on the aperture scale. It is curious to me why the difference in the scale markings. Somebody out there in APUG land probably has some insight on this. By the way, I plan to use this vintage French camera to capture some ikonic (it's not just a Zeiss word ;-}) French landmarks during my September invasion of the continent. I also have a 1941 Argus C3 (ala Tony Vaccaro) to use while in the Normandy invasion locales.

Thanks for all responses.

Jim

 

[frank]

That is an old and discontinued aperture scale. Ive heard it called the Continental scale. I have a leitz lens like that. Just interpolate like you surmised. Other old aperture scale systems require conversion charts, but not this one.

 

[AgX]

Was one invasion not enough? Do you really need to make another?

 

[IloveTLRs]

I have two pre-war Leitz lenses with non-standard aperture markings. You could have a look at this section of the Wikipedia article on F-numbers -- a "Comparative table of diaphragm numbers" which helped me.

 

[Jim Jones]

Long ago some lens apertures were marked in full stops from the largest aperture, as in the OP's example. It may seem less logical to one who uses a variety of lenses, but makes sense enough for a one-camera photographer.

 

[Ian C]

The obsolete aperture number sequence: f/6.3, f/9, f/12.5, f/18, f/25 passes 1/3 stop less light than the modern conventional sequence f/5.6, f/8, f/11, f/16, f/22.

Thus

f/6.3 passes 1/3 stop less light than f/5.6

f/9 passes 1/3 stop less light than f/8

f/12.5 passes 1/3 stop less light than f/11

f/18 passes 1/3 stop less light than f/16

f/25 passes 1/3 stop less light than f/22

 

[AgX]

So, if one started with an odd f-stop number with the largest aperture it made sense to go on with it for the smaller ones.

Unless exposure meters etc. got the even numbers...

 

[JPD]

Long ago some lens apertures were marked in full stops from the largest aperture, as in the OP's example.

This is not the case here. It's a normal and typical european aperture scale from that period. It's the same scale as the modern, just different numbers.

There's no need to interpolate on it, since the shutter speeds are slower. If your exposure meter says aperture 8 and 1/125 use aperture 9 and 1/100 sec.