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# Thread: light and f stop

1. Originally Posted by Claire Senft
So Edward, perhaps you can give me an example of where it does not equal a fraction. Perhaps you could also give me an example where a ratio does not result in a fraction. How different is 1:12 to 1/12?
Claire,
The size of the aperture opening is a fraction/ratio, but the "f" in f-stop stands for focal length, not fraction. So it is a fraction, but not for the reason you state.

To be more accurate, it's the "/" in the more correct "f/stop" that means fraction. not the "f" itself.

allan

2. I was always under the impression that it stood for focal length, since the apperture is expressed as f 1:x. But "fraction" seems to work - so whatever allows you to understand the principle, works for me. I was taught "focal length", but if I was taught "fraction" - I would get the same results, I think.
So not a good reason for WWIII, m'thinks

3. Didn't mean to start a war!!!!

4. doesnt take much to start a war here Tom

lee\c

5. Originally Posted by bohica
Didn't mean to start a war!!!!
You didn't start a war, you started an, um, enlightening discussion.

Cheers,

6. Originally Posted by gnashings
but if I was taught "fraction" - I would get the same results, I think.
But how would you know what value to put in the numerator of the fraction? :-)

7. Want me to send you a PM telling you?

8. Yeah, well - war or no war, I still love APUG!

9. I always thought that DOF increases with the distance to the subject. If you focus on infinity you get a lot more DOF than if you focus at something close, right? So if you compose a shot with a wide angle lens and stand, say 5 meters away, you'll have to stop down to f/stop X to get the DOF you want. Shot the same composition with a tele lens and you'll have to back up quite a bit to fit it all in. You'll find that you can use a wider apreture to get the same DOF. Becouse of the distance to the subject.

10. Anyone who has done macro with a LF camera and quickly run out of DoF (as you do) and then thought: "I know, I'll use a wider lens because that will give me more DoF" has soon found out that Dan is correct. Because you need to move the camera closer to the subject in order to maintain the same image size on the ground glass (read "magnification") your DoF goes back to the same as you had with the longer lens. No free lunch there unfortunately (and no arithmetic needed - just practical experience )

Cheers, Bob.

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