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manuals
12
Working diagram of the exposure meter
The diagram shows the relationship
between film speed Sv (speed value) and
brightness Bv (brightness value) on the one
hand, and between shutter speed Tv (time
value) and aperture Av (aperture value) on
the other, together with the resulting
exposure value Ev. The diagram is in two
parts connected by diagonal lines that
represent the exposure values Ev. A typical
example, marked in red, shows how these
values correlate. Assuming a film speed of
ISO 400/27°, follow the vertical line to the
point where it intersects with the horizontal
line for brightness, in this case 0.5 cd/m
2
,
typical for night-time photography.
A diagonal which passes through this point
of intersection leads to the relevant
exposure value, in this case Ev 4. Various
combinations of aperture and shutter speed
can produce this value, i.e. transfer to the
camera's working range.
For correct exposure, the points of inter-
section of the vertical Av and the horizontal
Tv lines must always lie exactly on a
diagonal Ev line. In the example, three such
combinations are shown: A = stop 2 at ¼s;
B = stop 8 at 4s; and C = stop 16 at 15s.
Each corresponds to the correct exposure
value.
In the modes shutter priority and aperture
priority, one of these values is preset, the
corresponding value is set automatically; in
automatic program mode, the camera auto-
matically sets both.