From:             Willem-Jan Markerink 
To:               eos@avocado.pc.helsinki.fi
Date sent:        Mon, 9 Jun 1997 19:59:53 +0000
Subject:          Re: EOS: What the heck is E-M?
Send reply to:    eos@avocado.pc.Helsinki.FI

On  9 Jun 97 at 12:23, Mr. Bill wrote:

> In an earlier posting regarding Full-Time-Manual focusing, Willem-Jan
> stated...
> 
> > This one is E-M too, like all large primes, ie no focus without
> > turning the camera on.
> 
> I understand USM, FTM, TS and L, but what the heck is "E-M?"

"Electronic Manual" focus, ie the manual ring and the focusing element
inside the lens are not mechanically connected, but by means of
motion detectors, and the focusing element is only moved by the USM
ring motor, not by mechanical means.
This design allows for variable AF speed when you focus manually, for 
either fast focus or very accurate focus (most important when using 
teleconverters, not sure if they slow down automagically when using 
those).
E-M is only present on the high end primes (plus the 28-80/2.8-4.0),
and only the big white lenses offer this variable focus speed (three
speed settings). On the 28-80/2.8-4.0 AF speed is varied
automatically over the focal range, and the 50/1.0 and 85/1.2 cannot
vary AF speed at all (they only share the same USM motor because of
the large aperture).



-- 
Bye,

Willem-Jan Markerink


      The desire to understand 
is sometimes far less intelligent than
     the inability to understand



[note: 'a-one' & 'en-el'!]

If you have any question, remark, comment, want to share some philosophy or just want to express your opinion about these pages, feel free to send email to: w.j.markerink @ a1.nl