An aperture question ?

[BADGER.BRAD]

This might sound like a stupid question but is an aperture (say f16) on one camera exactly the same physical size as on another ?

 

[sk66]

If the lens focal length (real, not effective) is the same then the aperture (or entrance pupil) is the same physical diameter.
Aperture is a lens characteristic, it's independent of the camera.

 

[Gaz J]

This might sound like a stupid question but is an aperture (say f16) on one camera exactly the same physical size as on another ?

Aperture size is a ratio of focal length to entrance pupil diameter.

f4 on a 100mm lens will give an aperture diameter of 25mm. f4 on a 50mm lens an aperture diameter of 12.5mm.

 

[Kodiak Qc]

Hi Brad,

there are no stupid questions… only stupid answers!

is an aperture (say f16) on one camera exactly the same physical size as on another ?

Aperture is not related to a camera but to a lens.

No, aperture is not an absolute measure like say a gram,
inch or K°. It is a relative scale applied to lenses where dif-
ferent lenses with different maximum aperture will have
different opening size at ƒ16 since it is relative to the maxi
mum.

So, the size of the opening is relative but not its value as
it expresses a ratio, a fraction in a precise way.

 

[Phil V]

It'd help if we always used the correct mathematical notation for aperture which is F/1:4 but we call it f4 or sometimes f/4

as you can see above f=focal length and the 4 is a ratio for the diameter. So for a 100mm lens the aperture diameter at f/4 is 25mm and at f/2 is 50mm

 

[StewartR]

It'd help if we always used the correct mathematical notation for aperture which is F/1:4 but we call it f4 or sometimes f/4

The trouble with using the word 'mathematical', Phil, is that it attracts the mathematicians. And we can be a pedantic lot.

Unfortunately F/1:4 is not correct. The slash indicates a ratio, and the colon indicates a ratio, but you don't need or want to use both of them together.

You could write f/4 which is interpreted as a quarter of the focal length. Personally I think that's the clearest. Unfortunately we tend to say it as f 4 without the slash, and of course slashes can't be used in filenames or URLs so we're pretty much forced to use f4 on computers. That's not so good.

Alternatively you could write 1:4 which is interpreted as a ratio; something is four times bigger than something else. Of course we all know it means the focal length is four times the aperture, but it's not explicit and therefore (to my mind) less satisfying.

Interestingly the manufacturers can't agree which is the best way to indicate aperture. Canon and Nikon both write 1:4 on the lens, but f/4 on the box the lens comes in. Sigma write 1:4 on the lens but f4 on the box. Tamron aren't consistent. Tokina are consistent and use f4 everywhere, so you might say they're consistently wrong. Sony and Zeiss seem to derive their nomenclature from a parallel universe: instead of 70-200mm f/4 they'd write 4/70-200. But they all agree that it's not f/1:4.

 

[gunnar]

Actually either of the following are correct notations:

F4 <--- upper case F but no slash (normally used to indicate the actual value a photograph was taken with)
f/4 <--- lower case f with a slash (normally used to indicate the the lenses maximum f number)
1:4

Whereas these are all incorrect:
f4
F/4
F/1:4
f/1:4

Some manufacturers also write smth like: 1.8/50
I will never understand the logic, surely it should be the other way around? i.e. 50/1.8 ?

 

[BADGER.BRAD]

Thanks everyone that now makes sense.