Conversions For your convenience, the modern shutter speed scale is printed on the face of the instrument graduated at 1/2 stop intervals. To convert any shutter speed to milliseconds, divide 1000 by the shutter speed. For example: the shutter speed of 25 is equal to 1000/25=40mS To obtain the half stop between any two full stops, take the geometric mean (square root of the product) of the two stops. For example, the half stop between 25 and 50 is (25X50)^1/2=35. Similarly, a quarter stop is obtained by taking the geometric mean of the full stop and the half stop. To convert milliseconds back to shutter speeds, divide 1000 by the millisecond. Thus when 23mS is displayed, the shutter speed is 1000/23=43.5 (half stop between 30 and 60). |
The "kink" in the shutter-speed scale The factor between the stops supposed to be 2. This, however, is not entirely true. In order to gain round numbers from start to finish on the scale, the factor between some of the stops is changed from 2 to some other value. This change in the factor places a "kink" into the smooth geometric progression. The old scale placed one severe "kink" between 2 and 5 (factor of 2.5) and another between 10 and 25 (factor of 2.5). Today, most often the "kink" occurs between 8 and 125 in either one or two steps. The progression 8, 16, 32, 64, 125 places a slight "kink" between 64 and 125 (factor of 1.95), while the progression 8, 15, 30, 60, 125 places two "kinks" in the scale that oppose each other: one between 8 and 15 (factor of 1.87) and another between 60 and 125 (factor of 2.08). Keep in mind, however, that these are just numbers printed on the dial. When the values 15, 30 and 60 are displayed the actual shutter speeds may be 16, 32 and 64. Older, mechanical shutters are not accurate enough for such nuances to make a difference, but these nuances may show up in top-of-the-line electronic shutters. |
Tolerances For older, mechanical shutters, a plus or minus half stop tolerance along the whole range is deemed to be acceptable by most technicians. A top quality mechanical shutter should be within plus or minus quarter of a stop. The best electronic metal square shutters are often accurate within plus or minus 10% of a stop. To get 10% on either side of any stop, multiply and divide the stop by the tenth root of 2, which is 1.07. Thus 10% tolerance for the shutter speed of 250 falls between 233 and 268 or in milliseconds between 4.29 and 3.73. These recommended tolerances are applicable along the whole shutter speed range and they include scatter. Individual stops may produce tighter tolerances. |
Scatter Due to friction, inertia and other mechanical or electronic factors, the time will be slightly different for each exposure. The scatter decreases as the quality of mechanism and electronics in the camera increases. Scatter is not the same as tolerance, but it should fall within the limits the tolerance sets. |
The modern scale at 1/4 stop intervals |
mS 2000 2681 1414 1189 1000 841 707 594 500 420 353 297 250 210 177 148 125 106 91 77 66 56 47 39 33 27 23 19 16.6 13.8 11.5 9.6 8.0 6.7 5.6 4.7 4.0 3.3 2.8 2.3 2.0 1.7 1.4 1.2 1.0 0.8 0.7 0.6 0.5 0.4 0.3 |
1/4 1.7sec 1.2sec 1.2 1.7 2.4 3.4 4.7 6.7 9 13 18 25 37 52 72 104 149 212 303 434 588 833 1189 1681 2378 |
1/2 1.4sec 1.4 2.8 5.6 11 21 43 87 178 357 714 1414 2828 |
stop 2sec 1sec 2 4 8 15 30 60 125 250 500 1000 2000 |
stop 8 16 32 64 125 |
mS 125 105 088 074 062 052 044 037 031 026 022 18.6 15.6 13.2 11.1 9.4 8.0 |
Alternate Scale between 8 and 125 |
1/4 9.5 13.5 19.2 27 38.5 53.7 75.7 106.3 |
1/2 11.3 22.7 45.4 90.1 |
Old Scale at 1/2 stop intervals |
mS 1000 714 500 316 200 141 100 63 40 28 20 14 10 7.0 5.0 3.5 3.3 2.5 1.7 1.2 |
1/2 1.4 3.16 7.1 16 35 71 143 285 588 |
stop 1 2 5 10 25 50 100 200 300 400 800 |
Shutter-speed Tables |
Shutter-speed Tables |
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Old Leica Scale at 1/2 stop intervals |
mS 1000 714 500 357 250 158 100 83.3 66.6 57.8 50.0 40.8 33.3 28.9 25.0 20.4 16.6 12.9 10.0 7.1 5.0 3.2 2.0 1.4 1.0 |
1/2 1.4 2.8 6.3 12 17 24 35 49 77 141 316 707 |
stop 1 2 4 10 15 20 30 40 60 100 200 500 1000 |