It calculates the difference in f/ stops between two stops you enter or you can enter in one f/ and the amount in f/ stops and it will calculate the difference second one for you.
F-Stop Calculator
F-Stop Calculator
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Here is a handy little site I just found
- Thread starter STM
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Fred Kingston_RIP
Senior Member
You need a calculator for that?????? 
You need a calculator for that??????
I do. I never seem to remember the f/stop sequence. It's easy to calculate ISO and shutter speed stops.
Sometimes you need a calculator, but that one is suspect.
Enter 6.1 and 7.2 and you get this:
Mine at Photographic Tables, Aperture f-stop, Shutter Speed, ISO and EV gives this:
EDIT: Oops! Hasty. I see now, it was adding to a f/stop value, but I was computing difference between two.
FWIW, you can use the same calculator
to enter two distances for direct flash, and it computes stops difference for the inverse square law.
That is at Four Flash Photography Basics we must know - Inverse Square Law
or enter two Flash Guide Numbers, and it computes stops difference (to be meaningful, of course both GN have to be for the same zoom or coverage, or at least the real numbers actually used).
It is at Compare Power Rating of Flashes with Guide Numbers
Or the f/stops.
Photographic Tables, Aperture f-stop, Shutter Speed, ISO and EV
But it is the same calculator (same formula).
Enter 6.1 and 7.2 and you get this:
Mine at Photographic Tables, Aperture f-stop, Shutter Speed, ISO and EV gives this:
EDIT: Oops! Hasty. I see now, it was adding to a f/stop value, but I was computing difference between two.
FWIW, you can use the same calculator
to enter two distances for direct flash, and it computes stops difference for the inverse square law.
That is at Four Flash Photography Basics we must know - Inverse Square Law
or enter two Flash Guide Numbers, and it computes stops difference (to be meaningful, of course both GN have to be for the same zoom or coverage, or at least the real numbers actually used).
It is at Compare Power Rating of Flashes with Guide Numbers
Or the f/stops.
Photographic Tables, Aperture f-stop, Shutter Speed, ISO and EV
But it is the same calculator (same formula).
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Fred Kingston_RIP
Senior Member
Here's a tip... Most of the Nikon cameras allow you to set/increment the light meter in 1/2, or 1/3 stop increments.... Turn that off so your camera increments the aperture in full 1 stop increments, then it becomes a simple 1-click turn of the aperture dial... or you can memorize the range from F2.8 to F22...
You really want exposures to only the nearest full stop precision? Each exposure could be off up to 1/2 stop? Just set it to 1/3 stop.
I pity the poor photographer who can't even remember those seven numbers. I was thinking, like, those numbers are on every lens. But I guess they are not anymore.
All that seems obvious, but the very best tip is if you meter your flashes with an incident meter, set it to 1/10 stops.
Then it reads like f/8 plus 0.7 stop or f/5.6 plus 0.2 stop. Then you can trivially know the difference in your head (obviously 1.5 stop here). And this bypasses the issue that what we round off and call f/11 is technically f/11.3, which matters in calculations.
I pity the poor photographer who can't even remember those seven numbers.
I was thinking, like, those numbers are on every lens. But I guess they are not anymore. All that seems obvious, but the very best tip is if you meter your flashes with an incident meter, set it to 1/10 stops.
Then it reads like f/8 plus 0.7 stop or f/5.6 plus 0.2 stop. Then you can trivially know the difference in your head (obviously 1.5 stop here). And this bypasses the issue that what we round off and call f/11 is technically f/11.3, which matters in calculations.
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