Question on Berthiot Perigraphe 90/F14 aperture reading

[gchu1970]

I recently got a Berthiot Perigraphe 90/F14 for my 5x7 format. But I don't how to read the aperture setting. It has a dial set aperture setting with marks "14, 20, 28, 40, 56" I don't know how to convert them to normal aperture reading, such as "16, 22, 32, 45, ..." Would like to seek some help in the forum.

[Dan Fromm]

Those are f/ numbers. f/14 is roughly 1/3 stop faster than f/16, f/20 roughly 1/3 stop faster than f/22, and so on.

[gchu1970]

I took a nice shot couple of days ago with this small lens on my Sinar P 57. Amazing result was obtained. Seems that it has enough coverage but little movement.

[Dan Fromm]

That sounds about right. Berthiot claims that f/14 Perigraphes cover 100 degrees. For a 90, that means 214 mm.