Reply to thread

Message: <blockquote data-quote="aroy" data-source="post: 304075" data-attributes="member: 16090">Here is how the lense aperture works.. On very old lenses, you set the aperture on the lense and the iris closed to it. For focusing you pushed a lever to open the iris.. Next came the "auto mode". Here the lense has a small lever on the mount, which moves the iris blades. At one end the lever opes the iris fully. At the other end it stops it down to the aperture set on the lense. When mounted, the aperture on the lense is fully open. When exposing the lever pushes the iris to the set aperture.. With coming of AF, the camera incorporated a lot of electronics. Now the aperture lever could be used to control the aperture in a step less manner, hence the lense was left at its maximum aperture. The camera controlled at what aperture the image was taken. That is how "Shutter Priority" worked.. With CPU in lenses, the lense could now have all its characteristics encoded and report to the camera the Maximum, Minimum and the current aperture, as well as the distance at which it was focused.AF lenses have a CPU. So the camera can control the aperture settings. This is true of the AF-S, AF-D and AF lenses. The non CPU lenses, like AIS, cannot tell the camera where the aperture is set, except by the "Rabbit Ears" (which is the mechanical linkage between the lense and the body to report at what aperture the lense is set).That is why with older lenses, you have to set the aperture manually, and tell the camera that, so that it can meter. The metering is done at open aperture, when exposing the iris closes to the aperture set on the lense.</blockquote>

Verification