|View camera lens set to f/8+1/2|
OT: Set the camera to 8-and-1/2
NB: (thinking to self) Hmm, my options are f/8, f/9, f/10, and f/11 (1/3 stop increments). I'll set it to f/9.
OT: Looks like we're slightly overerexposed. Are you really at 8-and-1/2?
NB: I don't see an 8.5, should I be at f/8 or f/9?
OT: 9? Where did that come from? I want it set halfway between 8 and 11.
NB: OK, I can set the camera to give me 1/2 stop increments. But then I'm at F/9.5. Is that what you want?
NB: Then why did you ask for 8.5?
OT: I didn't ask for 8.5, I asked for 8-and-1/2
NB: Isn't 8-and-1/2 equal to 8.5?
OT: No, 8-and-1/2 is equal to 9.5.
And they go back and forth for an hour or so.
|Canon FD lens set to f/8+1/2|
|Canon EOS camera set to f/8+1/2|
Here are three charts of aperture values:
1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32
1.7, 2.46, 3.4, 4.8, 6.7, 9.5, 13.5, 19.6, 27
1.6, 1.8, 2.2, 2.5, 3.2, 3.5, 4.5, 5, 6.3, 7, 9, 10, 12.5, 14, 18, 20, 25, 28
In "old timer terms" the progression in half-stops is:
1.4, 1.4+1/2, 2, 2+1/2, 2.8, 2.8+1/2, 4, 4+1/2, 5.6, 5.6+1/2, 8, 8+1/2, 11, 11+1/2, 16, 16+1/2, 22
Newer photographers using electronic cameras (film or digital) might refer to the same progression as:
1.4, 1.7, 2, 2.46, 2.8, 3.4, 4, 4.8, 5.6, 6.7, 8, 9.5, 11, 13.5, 16, 19.6, 22
You need to know which "language" each is speaking in when telling one another to set an aperture on a lens.
Another place this comes into play is in using hand-held meters. My old Minolta Flash Meter III read in 1/10th stops. So, in the same scenario as above, the flash meter might read f/8-and-5/10s which you could read out as f/8+1/2, but which translates to f/9.5. 8-and-7/10s would translate to f/10.
With most cameras now allowing you to set your aperture via a dial on the body instead of on the lens this may seem a bit pedantic. But with the resurgence in interest in film cameras or in modifying lens mounts to allow old lenses to be mounted on a digital camera so you have to set the aperture on the lens itself, it is worth knowing about.
More about aperture numbers in an earlier blog post.
*many older lenses had 1/2 stop indents so that you could set the lens between two full stop settings. And some camera repair shops could modify lenses to have 1/3 stop detents.