Canon EOS 1Ds Mark II Instruction Manual page 167

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If you do not change the focusing screen that came with the camera, you
need not change C.Fn-00-1 factory setting.
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To change the focusing screen, refer to the instructions that came with
the focusing screen.
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The Ec-A, Ec-B, Ec-I, and Ec-L focusing screens have a prism at the
center. A correct exposure reading cannot be obtained with evaluative
metering or spot metering based on the center area where there is a
prism. Use centerweighted averaged metering or off-center spot
metering with such focusing screens.
Ec-series Interchangeable Focusing Screens
Ec-A: Standard microprism
Ec-B: New split screen
Ec-CII: All Laser-matte
Ec-CIII: Laser-matte
Ec-D: Laser-matte with grid
Ec-H: Laser-matte with scale
Ec-I: Laser-matte with cross hair
Ec-L: Cross split screen
Ec-N: New Laser-matte
Ec-R: New Laser-matte
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