French Aperture System on Hermagis WA lens

[cwe001]

Here i got a Hermagis Wideangle Aplanat about 6 1/4 inch focus.

The wheel stop read 4,8,16,32,64 changing in factor of 2.

It is like US system at first sight but at largest apeture 4, the apeture hole on the stop is only about 8mm, which makes 4 corresponds to somewhere at f16~f20

Any enlightment from here? What is French f:1 ?

Lens is even smaller than cook ViiB o_o

 

[Ole]

The old French aperture 1 is f:10. So your WA Aplanat is f:20.

 

[cwe001]

f/20 sounds quite appropriate for the size of aperture hole.

I wonder it may have 110+ degree coverage....en, coverage for wide lens seems f8<f12.5<f18<f20

Baought it for $70,
a black white polaroid image from this tiny lens is very crisp and feels 'contrasty',better than one uncoated cooke Viib I sold for $400

 

[Ole]

Some of those WA Aplanats were sold as 100 to 110 degrees coverage, yes.

My little 150mm Busch Weitwinkel Aplanat ser.C no 2 just about covers 24x30cm, or 9.5x12". That's an image circle of 380mm, so just a fraction more than 100 degrees.