How to calculate stops?

How do you calculate stops?
say I want to know how many stops from f/1.8 to f11
I thought that a stop was double or half. But it doesnt seem to be when talking f-stops
Excuse my ignorance on the subject. I just never got it.

For aperture is 1.4x, or more precisely the square root of 2.

So f/2 -> f/2.8 is one stop, and f/2.8 -> f/4 is one more stop.

So doubling the f-number for aperture is 2 stops.

This is because its the area of the circle which counts, since this is proportional to the diameter squared, we have to increase this ratio by the square root of two to double the area.

Or just count the clicks from whatever aperture your in..?

RSMarco wrote in post #14586515
Or just count the clicks from whatever aperture your in..?

Provided you know that by default the camera clicks off 1/3 stops, changeable in the menu to 1/2 stops.

For shutter speed the number displayed is the denominator of the fraction of a second the shutter is open, so doubling the number halves the time which equals one stop.

1.8 to 2=1/3 stop
2 to 2.8=1 stop
2.8 to 4=1 stop
4 to 5.6=1 stop
5.6 to 8=1 stop
8 to 11=1 stop

Therefore 5 and 1/3 stops from f1.8 to f11

As stated above whole f-numbers are powers of the square root of 2.

nth whole f stop=1.414^n

1.414^1=1.4, 1.414^2=2, 1.414^3=2.8...

Try it with a calculator, you'll see all the familiar f-numbers(rounded to 1 decimal for single digit f-numbers, otherwise rounded to whole numbers).

multiplying by 1.4 (or the square root of 2) will get you to the next whole stop.
the cube root of that (or the 6th root of 2) will get you to the next 1/3 stop.

just wanted to add that in since I finally figured out how to calculate 1/3 of a stop w/ aperture (the multiplication w/ square roots really confused me...plus I was trying to calculate 1/3 stops like you would for ISO or shutter speed for a while).

Damnn, this feels like highschool all over again

OP is correct that a stop is a doubling or halving of the light. This is related to the area of the aperture. The only difficulty is that we report aperture as the ratio of the diameter to the focal length, and so the f/stop is a diameter term. Area is related to the square of the diameter.

In the field, the easiest way to think of whole stops is to start with two values, f/1.0 and f/1.4. Now look at two doubling sequences:

f/1.0 - f/2.0 - f/4.0 - f/8.0 - f/16.....
f/1.4 - f/2.8 - f/5.6 - f/11 - f/22.....

These two sequences of doubling give all of the whole stops in one stop increments. Just read top line, bottom line, top line, bottom line as in f/1.0 - f/1.4 - f/2.0 - f/2.8 - f/4.0 - f/5.6 etc.

JeffreyG wrote in post #14587018
OP is correct that a stop is a doubling or halving of the light. This is related to the area of the aperture. The only difficulty is that we report aperture as the ratio of the diameter to the focal length, and so the f/stop is a diameter term. Area is related to the square of the diameter.

In the field, the easiest way to think of whole stops is to start with two values, f/1.0 and f/1.4. Now look at two doubling sequences:

f/1.0 - f/2.0 - f/4.0 - f/8.0 - f/16.....
f/1.4 - f/2.8 - f/5.6 - f/11 - f/22.....

These two sequences of doubling give all of the whole stops in one stop increments. Just read top line, bottom line, top line, bottom line as in f/1.0 - f/1.4 - f/2.0 - f/2.8 - f/4.0 - f/5.6 etc.

I knew there had to be an easier way. Thanks!
No calculator needed.

There used to be a wristband going around with the f stops printed on it showing all in 1/3 stops from 1 to 32 but I just had a look on ebay and can't find it any more. Like the OP I'm getting terrible at remembering them. There used to be another band with all the shutter speeds in 1/3 stops as well, but I can't even find one of those either. Would be an easy way to remember though, if you could find one.

Agree with comment above, much easier to remember instead of calculating.
This is why I like old full manual lenses, don't have to remember or calculate

Likewise for ISO stops. 100>200>400>800>1600>3200>6400>12800... are one stop increments.