Focal plane shutter
Shutters are designed to allow the time to be changed by a factor of
2. That is, each change of shutter speed will alter the exposure time by
either doubling it or halving it. It is no coincidence that shutter speeds
are designed this way. Do you suppose that it has anything to do with the
fact that f/numbers also work by doubling and halving? There are two common
sequences of shutter speeds, depending on the type of shutter.
plane shutter sequence is shown in Table 1-3, and the leaf shutter speed
sequence in Table 1-4. See a shutter speed scale for a focal plane shutter
in Figure 1-9, and for a leaf shutter lens in Figure 1-10.
A focal plane shutter speed sequence
Figure 1-9. Top of a 35 mm camera showing the shutter
speed scale for a focal plane shutter