The
Nikon F4
by
J. Ramón Palacios tell
a friend about this article
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THE
EXPOSURE METERING SYSTEM
As
said before, in the Nikon purist engineering tradition it took
a decade to perfect a flagship, but it was finally here, exactly
30 years after the first Nikon F (1959-1989).
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The
author and his son under
bright sunlight and harsh shadows in the high mountains
of Keystone Colorado. Nikon F4s with Nikkor 35-135mm f/3.5-4.5,
TTL fill flash from a SB-25 on self-timer.
.
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The DP-20,
the standard finder on the F4, not only offers 100% of the
picture field and -for the first time- a diopter correction
knob, but also performs the metering modes, Matrix, Center-Weighted,
and the third, Spot, to cope with any type of lighting situation.
Furthermore, the F4 does not require a lens to have a CPU
to be able to function in the matrix metering mode, therefore
allowing for full use of all pre-AI, AI and AI-S lenses, and
of course those that have a CPU. To do this, it has 4 integrated
circuits including a 8 bit microcomputer.
Contrary
to general belief, matrix metering is ideally suited for difficult
lighting and manual exposure compensation becomes unneeded,
even when there are strongly different areas of brightness in
a scene. To make it work, the F4 has two photo diodes, each
consisting of three sensors which meter the frame divided into
five segments. Once the measurements of brightness and contrast
are made, they are transmitted to the high capacity computer
which in turn, using Nikon proprietary software, evaluates such
brightness and contrast patterns, arranging the information
according to 25 matrix boxes, each of which contains one or
more algorithms. After analyzing the light patterns of the scene
it goes on to determine the appropriate computation method averaging
the extremes of light and contrast and in the end deciding what
should be the recommended exposure, after comparing the scene
to the 100,000 brightness and contrast range combinations stored
in its data bank. The speed at which it performs this task is
-of course- instantaneous!
Center
Weighted metering works with 60% of the meter's sensitivity
on the 12mm circle in the center of the screen; the other 40%
of the information required to compute an exposure is derived
from the rest of the screen.
Spot
metering, best suited for very precise and selective metering
of smaller subjects within the frame, is performed within the
confines of a 5mm diameter circle in the viewfinder.
When
fill flash is required -like in the picture above- metering
data combines to balance the exposure on both the subject and
the background. Based on data stored for general brightness
and contrast scenes, the meter and the microcomputer perform
a five methods computation to decide whether the picture should
be taken as low brightness weighted, average, center weighted
or high brightness weighted.
In
the hope that I have not confused you much, let me just say
that it works like nothing before. It is not until the advent
of the F5, with its RGB matrix metering (a meter that also sees
color) that a camera meter could be said to have improved upon
that of the F4. |
