How is the shutter speed scale structured?

The shutter scale is structured in such a manner that each division lets in half or twice as much light depending on the direction the shutter control is moved. This corresponds in effect to the aperture scale as far as exposure is concerned, with the difference between each setting equal to what is called one stop, but rather than control the amount of light as the aperture does, the shutter controls the length of time the light exposes the emulsion for.

The scale on many cameras might run as the following sequence: Again each division is referenced as a stop.

Shutter speed	comparative units of light transmitted	differential in STOPS
1/4000	1	0
1/2000	2	1
1/1000	4	2
1/500	8	3
1/250	16	4
1/125	32	5
1/60	64	6
1/30	128	7
1/15	256	8
1/8	512	9
1/4	1024	10
1/2	2048	11
1 sec	4096	12
2 sec	8192	13
4 sec	16384	14
8 sec	32768	15
15 Sec	65536	16
30 Sec	131072	32

We see these speeds transposed onto the shutter dial of this 35mm SLR film camera -

In most digital cameras this information is illuminated in the viewfinder - not all the shutter speed numbers are visible in the viewfinder usually there is the selected setting and perhaps one either side.

Many of current digital cameras also allow 1/2 or 1/3 stop increments.

For instance a camera with 1/2 stop shutter increments would have 1/4 - 1/6 1/8 sec

1/6sec is a half stop

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