For those of us who use also use Nikons. heres a little device.
(http://filmprocess.ru/images/oduvanchik/dandelion_nikons.jpg)
(http://nikonrumors.com/wp-content/uploads/2010/06/nikon-chip1.jpg)
It sticks to the Nikon adapter and informs the camera of the focal length & aperture of whatever is connected to it.
Its fully programmable. so you can use it with whatever scope / manual lens's you have.
It will also allow your camera to indicate if the image is in focus.
Write up: http://filmprocess.ru/nikon_spec_en.htm (http://filmprocess.ru/nikon_spec_en.htm)
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Mac.