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can someone pls give me a dumbed down version of the differences between Ai and Ais.

Rooz, to save some writing read the first few pages of this, always makes for interesting reading and imparts a lot of info re the early lenses

http://www.mir.com.my/rb/photography/co ... /index.htm

To a modern camera that support AI lenses, it means absolutely the same thing. They both are AI coupled through the ring on the camera to tell the body what aperture the lens is on.

For older lenses they might be slightly different when using those FA or ealier bodies.

Some more info here:
http://www.cameraquest.com/aidaiais.htm

excellent links. thanx.
this is the bit i really wanted to know...

If you plan to use manual lenses with current AF bodies, think twice before paying extra for AIS lenses. They seldom offer any benefit!