"US" Fstops

[N Dhananjay]

based on the fact the US number system is old you say 256=64[Then double or halve for each US number. US256=f64; 128=f45; 64=f32; 32=f22; 16=f16; 8=f11; 4=f8; 2.8=f6.8] now I have a scale that starts at 4 \\ 6 \\ 12 \\ 24 \\ 48 \\ 96\\
Now is this a US number scale or something else: thanks all:

There are a number of different systems used (US or uniform stops, Stolze, Zeiss etc). The modern system uses f=F/n where F is focal length and n is diameter the aperture. The US system uses f^2/16 (thus f/16 + US 16). The Stolze system uses f^2/10 (so f/10 = Stolze 10).

Stolze --- modern f-stop system -- US

1.6 --- 4 ---- 1
3.14 --- 5.6 --- 2
6.4 --- 8 ----- 4
12.1 --- 11 ---- 8
25.6 --- 16 --> 16
48.4 --- 22 --- 32
102.4 --- 32 --- 64
202.5 --- 45 --- 128
409.6 --- 64 --- 256

I'm guessing what you have is some other system (Zeiss used some systems devised by Rudolph) utilizing a doubling and the first one (4) is probably just the full open state (sort of like a normal system that starts at f/7.7 and then going f/8, f11 etc). Cheers, DJ