What constitutes a 'stop'?

[terry.langham]

Been looking for a quick reference chart to work out the difference in highlight and shadow EV's to make selecting GND's a bit easier. Haven't had much luck, so thought I would have a go at knocking one up myself. Looking at the Jiffy calculator, are the aperture and shutter speed listed in 1/3 or 1/2 stop increments?

Cheers

[Xenedis]

Those are listed in third stops (and half-stops where appropriate).

For your convenience, here's a quick list of f/stops from f/1 to f/16, with the incremental distance noted.

1. f/1 (full-stop)
2. f/1.2 (half-stop)
3. f/1.4 (full-stop)
4. f/1.6 (third-stop)
5. f/1.8 (third-stop)
6. f/2 (full-stop)
7. f/2.2 (third-stop)
8. f/2.5 (third-stop)
9. f/2.8 (full-stop)
10. f/3.2 (third-stop)
11. f/3.5 (third-stop)
12. f/4 (full-stop)
13. f/4.5 (third-stop)
14. f/5 (third-stop)
15. f/5.6 (full-stop)
16. f/6.3 (third-stop)
17. f/7.1 (third-stop)
18. f/8 (full-stop)
19. f/9 (third-stop)
20. f/10 (third-stop)
21. f/11 (full-stop)
22. f/13 (third-stop)
23. f/14 (third-stop)
24. f/11 (full-stop)

HTH.

PS: Note that f/1.2 is the only half-stop in that range.

[etherial]

A stop put simply is the doubling or halving of light. ie f4 to f5.6 is one stop, 1/100 to 1/200 is one stop, ISO400 to ISO800 is one stop.

[Kym]

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[ameerat42]

What constitutes a 'stop'?

Well, Terry, taking your question more generally, a cessation of motion relative to an observer should fit the bill.

But back to photography, I once had an old camera (an Agfa I think) that had a continuous aperture adjustment. It had "STOP" signs marked, like f/4, f/5.6, but stopping at them was optional, and at best approximate, rather more like "Give Way" signs.