III. NEW AND IMPROVED DESIGN FEATURES 10
E-TTL II Flash System
As
with the EOS-1D Mark II, the AF CPU of the 1Ds Mark II is a 33 MHz, 32-bit RISC
(r
educed instruction set) microcomputer that handles area AF detection and auto AF
point
selection. The 1Ds Mark II camera CPU is a 32 MHz, 32-bit RISC microcomputer
th
at controls lens communications, lens driving control and predictive AF statistical
c
alculations. As a result, all the processing is faster than with the EOS 1D and 1Ds. One-
Shot
AF speed is faster; AI SERVO AF focusing precision is the same for the 1D Mark II
and the 1D
s Mark II and appreciably greater than that of their predecessors.
Because the AF unit is capable of operating at 8.5 frames-per-second and the 1Ds Mark
II has a maximum speed of 4 fps, the AI Servo AF algorithm has been optimized for 4 fps
operation. “C-Fn 21 AI SERVO AF continuous shooting and shutter speed priority” of the
EOS-1D Mark II is deleted for the 1Ds Mark II for the same reason. The 1Ds Mark II can
track a moving subject easily and shoot at 4 fps, so without setting C-Fn 21, it can
operate at the maximum continuous shooting speed.
Since the first photographer set a house on fire with blitzlichtpulver (flash powder) more
than a hundred years ago, low-light shooters have waited patiently for E-TTL II, the
complete solution to flash control.
The EOS-1Ds Mark II shares the new E-TTL II algorithm with the EOS-1D Mark II. The
system enables uncanny E-TTL flash accuracy and reliability. In previous cameras,
evaluative flash metering was based on the assumption that an autofocus point would
cover the subject. When this is not the case, inaccurate flash exposures result. The
EOS-1Ds Mark II’s evaluative flash metering is not dependent on the active AF point.
In the new al
gorithm, ambient light is measured when the shutter button is pressed.
Next, a pre-flash is fired and the metering sensor takes readings at the central 17
metering zones. The ambient and pre-flash readings are compared. The metering areas
having a small difference are selected as the flash exposure metering areas. (Areas with
very big differences between ambient and pre-flash readings are excluded or down
weighted because they are assumed to contain a highly reflective object or that the
subject is not in that part of the frame. The algorithm avoids chronic underexposure
problems in such situations.) These readings are weighted, averaged and compared
with the ambient light reading, and the main flash output is then set and stored in
memory. E-TTL II weights and averages the flash metering for the subject and all other
objects at the same distance as the subject. Even if the subject’s position, reflectance or
size changes, the flash output will not change radically. The flash exposure will be highly
accurate and stable.
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