Canon EOS1 Ds MARKII Design And Performance

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Canon EOS1 Ds MARKII Design And Performance Manual pdf 10 page image

III. NEW AND IMPROVED DESIGN FEATURES 10E-TTL II Flash SystemAs with the EOS-1D Mark II, the AF CPU of the 1Ds Mark II is a 33 MHz, 32-bit RISC(reduced instruction set) microcomputer that handles area AF detection and auto AFpoint selection. The 1Ds Mark II camera CPU is a 32 MHz, 32-bit RISC microcomputerthat controls lens communications, lens driving control and predictive AF statisticalcalculations. 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 IIand the 1Ds 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 MarkII has a maximum speed of 4 fps, the AI Servo AF algorithm has been optimized for 4 fpsoperation. “C-Fn 21 AI SERVO AF continuous shooting and shutter speed priority” of theEOS-1D Mark II is deleted for the 1Ds Mark II for the same reason. The 1Ds Mark II cantrack a moving subject easily and shoot at 4 fps, so without setting C-Fn 21, it canoperate at the maximum continuous shooting speed.Since the first photographer set a house on fire with blitzlichtpulver (flash powder) morethan a hundred years ago, low-light shooters have waited patiently for E-TTL II, thecomplete solution to flash control.The EOS-1Ds Mark II shares the new E-TTL II algorithm with the EOS-1D Mark II. Thesystem enables uncanny E-TTL flash accuracy and reliability. In previous cameras,evaluative flash metering was based on the assumption that an autofocus point wouldcover the subject. When this is not the case, inaccurate flash exposures result. TheEOS-1Ds Mark II’s evaluative flash metering is not dependent on the active AF point.In the new algorithm, 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 17metering zones. The ambient and pre-flash readings are compared. The metering areashaving a small difference are selected as the flash exposure metering areas. (Areas withvery big differences between ambient and pre-flash readings are excluded or downweighted because they are assumed to contain a highly reflective object or that thesubject is not in that part of the frame. The algorithm avoids chronic underexposureproblems in such situations.) These readings are weighted, averaged and comparedwith the ambient light reading, and the main flash output is then set and stored inmemory. E-TTL II weights and averages the flash metering for the subject and all otherobjects at the same distance as the subject. Even if the subject’s position, reflectance orsize changes, the flash output will not change radically. The flash exposure will be highlyaccurate and stable.