A leaf shutter speed sequence
Front of a leaf shutter lens showing
shutter speed scale
(These numbers represent fractions of a second.
When you see 250, read
a. As you can see, neither shutter sequence exactly changes the times
by two; they only approximate. The true sequence would be as in Table 1-5.
A theoretically perfect shutter speed sequence
The reason for this is that to divide the shutter times exactly would
require a very complicated set of gears. Also, as with the f/numbers, such
precision isn't really necessary.
b. The time "T", and bulb "B" settings are for shutter speeds longer
than one second. When the shutter is set to "T", two actions are required:
the shutter release is tripped once to open the shutter, then tripped again
to close it. This setting is usually found only on leaf-type shutters. The
"B" setting is a little different. Pressing the shutter release opens the
lens, and the lens stays open only so long as pressure is maintained on the
release. Letting go will cause the lens to close immediately. This setting
is almost always operated by using a cable release - a long flexible cord
which attaches to the shutter release and has a plunger which trips the
shutter (fig 1-11).