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Exposure calculator

This rule of thumb exposure calculator came out of a book long ago; I've no idea which book. At the time, I converted the rules into a 3-rotor cardboard calculator, which I recently found again. The following rules have been worked back from the calculator. They are intended for the UK.

Take the value from Table 1 according to the scene, then add the factors for weather from Table 2, time of day and season from Table 3, and film speed from Table 4. Look up the final sum in the body of Table 5, and read off possible aperture and shutter speeds from the headings.

Table 1

Scene Value
Groups in shade 4
Groups in open 5
Open streets 6
Landscapes with bright foregrounds 7
Distant landscapes 8

Table 2

Weather Add
Dull 0
Medium cloud 1
Light cloud 2
Clear 3

Table 3

Month Add
Time of day
07..09 09..11 11..14 14..16 16..18
Nov Dec Jan   1 2 1  
Feb Mar Sep Oct 0 2 3 2 0
Apr May Jun Jul Aug 2 3 3 3 2

Table 4

Film speed (ISO) Add
10..20 0
20..40 1
40..80 2
80..160 3
160..320 4
320..640 5
640..1280 6

Table 5

Shutter speed
(sec) 		Total
Aperture (f/)
1.4 2 2.8 4 5.6 8 11 16 22 32
1/1000 11 12 13 14 15 16 17 18 19 20
1/500 10 11 12 13 14 15 16 17 18 19
1/250 9 10 11 12 13 14 15 16 17 18
1/125 8 9 10 11 12 13 14 15 16 17
1/60 7 8 9 10 11 12 13 14 15 16
1/30 6 7 8 9 10 11 12 13 14 15
1/15 5 6 7 8 9 10 11 12 13 14
1/8 4 5 6 7 8 9 10 11 12 13
1/4   4 5 6 7 8 9 10 11 12
1/2     4 5 6 7 8 9 10 11
1       4 5 6 7 8 9 10
2         4 5 6 7 8 9
4           4 5 6 7 8

 

 

The original calculator

Views of the two sides of my original cardboard calculator, dating probably from around 1970.

side 1

side 2

nib 1996-07-14 .. 2007-12-07

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