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F/Stops

Read down a column to find intermediate f/stops. For example, if you want to find out what f/stop is 1/2 of a stop between f/2.8 and f/4, find the +1/2 row at the left and then read across to the f/2.8 column and you will see f/3.4.

F# 1.4 2 2.8 4 5.6 8 11
+1/4 1.5 2.2 3.0 4.4 6.0 8.7 12
+1/3 1.6 2.24 3.2 4.5 6.4 9.0 12.8
+1/2 1.7 2.4 3.4 4.8 6.7 9.5 13.4
+2/3 1.75 2.5 3.5 5.0 7.0 10 14
+3/4 1.8 2.6 3.6 5.2 7.3 10.4 14.6
+1 2 2.8 4 5.6 8 11 16

Calculating the difference between F/Stops

To directly calculate the number of f/stops difference between two f/numbers, divide the larger by the smaller number, and read from the list below.

  • 1.09 = 1/4 stop
  • 1.12 = 1/3 stop
  • 1.19 = 1/2 stop
  • 1.25 = 2/3 stop
  • 1.29 = 3/4 stop
  • 1.41 = 1 stop

For example, how much slower is an f/3.5 lens than an f/2.8 lens?

Divide 3.5 by 2.8 = 1.25

1.25 on the list above indicates that f/3.5 is 2/3 of a stop slower than f/2.8.


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