Those listed are full stops. Most cameras allow you to increment shutter speed and aperture in half-stops or one-third stops, and you can select intermediate values manually.
- If you have the camera set to half-stops, then you'll have 1/350 between 1/250 and 1/500.
- If you have 1/3 stop increments set, you'll have 1/320 and 1/400
To work these out, a full stop is double the light. A half stop then is the square root of 2 times, or 1.4 (so that if you go up a half stop, then another half stop, you multiply the 1.4 factor together, and 1.4 * 1.4 = 2, which is your full stop)
- So 250 times 1.4 = 350
- and 350 * 1.4 = 500
For 1/3 stops, it's the cube root of 2, or 1.26x
- 250 * 1.26 = 315 (rounded to 320)
- 315 * 1.26 = 396 (rounded to 400)
- 396 * 1.26 = 500
Note that numbers are rounded, considerably in some cases, for convenience. The actual shutter speeds the camera produces are probably more precise values than these.
1/2 1/3<br/>
Stops Stops
<kbd>1000</kbd><kbd>1000</kbd><br/>
<kbd>750 </kbd><kbd>800 </kbd><br/>
<kbd>500 </kbd><kbd>640 </kbd><br/>
<kbd>350 </kbd><kbd>500 </kbd><br/>
<kbd>250 </kbd><kbd>400 </kbd><br/>
<kbd>180 </kbd><kbd>320 </kbd><br/>
<kbd>125 </kbd><kbd>250 </kbd><br/>
<kbd>90 </kbd><kbd>200 </kbd><br/>
<kbd>60 </kbd><kbd>160 </kbd><br/>
<kbd>45 </kbd><kbd>125 </kbd><br/>
<kbd>30 </kbd><kbd>100 </kbd><br/>
<kbd>23 </kbd><kbd>80 </kbd><br/>
<kbd>15 </kbd><kbd>60 </kbd><br/>
<kbd>11 </kbd><kbd>50 </kbd><br/>
<kbd>8 </kbd><kbd>40 </kbd><br/>
<kbd>6 </kbd><kbd>30 </kbd><br/>
<kbd>4 </kbd><kbd>25 </kbd><br/>
<kbd>3 </kbd><kbd>20 </kbd><br/>
<kbd>2 </kbd><kbd>15 </kbd><br/>
<kbd>1.5 </kbd><kbd>13 </kbd><br/>
<kbd>1 </kbd><kbd>10 </kbd><br/>
<kbd> </kbd><kbd>8 </kbd><br/>
<kbd> </kbd><kbd>6 </kbd><br/>
<kbd> </kbd><kbd>5 </kbd><br/>
<kbd> </kbd><kbd>4 </kbd><br/>
<kbd> </kbd><kbd>3 </kbd><br/>
<kbd> </kbd><kbd>2.5 </kbd><br/>
<kbd> </kbd><kbd>2 </kbd><br/>
<kbd> </kbd><kbd>1.6 </kbd><br/>
<kbd> </kbd><kbd>1.3 </kbd><br/>
<kbd> </kbd><kbd>1 </kbd><br/>