What does the note “19/65 21/90 22/130” on a Zenit 12XP mean?

Question

I found an old Zenit 12XP with a HELIOS-44M-4 58mm f/2 lens. The camera has a film speed scale marked ГОСТ/ASA with settings like 16, 32, 65, 130, 250, 500. A note stuck on the back reads: “19/65 21/90 22/130”.

What do these numbers mean, and how would they have been used when setting up the camera?

user89902 · Accepted Answer

Those look like DIN speeds that match values on the GOST meter dial.

GOST was the Soviet film speed standard; it was on the same scale as ASA speed, but 90% the value (so GOST 360 was equivalent to ASA 400).

DIN works like dB, in that each change by 3 doubles or halves the value; that means DIN 24 is ASA 200, 21 is ASA 100, and so forth -- so those figures give 22 as 130, 21 as 90 -- which are the GOST speeds that correspond to FP4+ and Plus-X, while 19/65 is about what you'd have for one generation Kodacolor.

What does the note “19/65 21/90 22/130” on a Zenit 12XP mean?

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