Contax AX Instruction Manual page 58

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Set the exposure mode selector lever to "Av." r)
Set the aperture and shoot.
a. When setting the aperture with the lens' aperture
ring, the camera will automatically set the shutter speed
suited for it.
In the viewfinder, the aperture you have set and the
shutter speed automatically set by the camera will turn
on.
It does not matter where the shutter speed dial is set.
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