When I google "shutter speed" and explore a few first hits, there is always listed only the standard shutter speeds - 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15 etc
But, when I go looking at photos in Flickr, I sometimes see photos taken with shutter speeds like 1/320 or 1/80 and similar oddities.
Where do these odd speeds come from?
I know we are talking about electronic devices here, so naturally we are not tied to the old mechanical camera limitations. So, can a shutter speed 1/320 be manually chosen in a modern digicamera, or is it a product of camera set to Auto-mode?
Answer
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
Stops Stops
10001000
750 800
500 640
350 500
250 400
180 320
125 250
90 200
60 160
45 125
30 100
23 80
15 60
11 50
8 40
6 30
4 25
3 20
2 15
1.5 13
1 10
8
6
5
4
3
2.5
2
1.6
1.3
1
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