From the Pentax FAQ at
http://www.sm.luth.se/~jem/foto/pfaq/cameras/c35m.html
What is ME-F ?
ME-F is an early attempt of Pentax on autofocusing. It is claimed to be
the first autofocus SLR employing a TTL autofocus sensor. It was
introduced in the early 80s with a 35-70 autofocus lens. The lens has an
internal motor inside just like F3AF and the modern Canon EOS. At that
time, the internal motor is big and heavy, the autofocusing of the
camera leaves something to be desired (it was tested to be as poor as
F3AF). As a result, the ME-F had the same fate of Nikon F3AF and Canon
T80 of the same era.
However, the ME-F employs the standard K-mount. The significance of ME-F
nowadays is that you get an ME-super with a so-so quality electronic
in-focus indicator. The 35-70 AF lens for ME-F will not
autofocus on the SF/Z/PZ series of bodies. The current F and FA lenses
will not autofocus on ME-F either.
--
Bo-Ming Tong 唐寶明