From: phg+@CS.CMU.EDU (Paul Gleichauf)
Newsgroups: rec.photo
Subject: Re: A FAQ
Date: 31 Aug 92 22:56:23 GMT
Distribution: usa
Organization: Carnegie Mellon University

In article <1992Aug31.200909.9909@PacBell.COM>, jpglori@srv.PacBell.COM (John P. Gloria) writes:
|> In article <1992Aug31.175701.7350@sj.nec.com> yi@tdd.sj.nec.com (Yi Zhang  x2912) writes:
...

|> >>For CANON-EOS, the auto focus motor is in the lens, 
|> >>while for NIKON the motor is in the camera body. 
|> >>
|> >>What are the advantages/disadvantages for these two different systems ? 
|> >> 
|> >>Y.Z.
|> ...
|> >The Canon lenses focus quicker.  If you hold a Canon AF camera
|> >and a Nikon AF camera, you will notice the difference
|> >immediately.
|> ...
|> Oops....I said in my earlier post if you held the both cameras
|> you would notice the difference immediately.  Of course, what
|> I meant is once you focused with them, you would notice the
|> difference.
|> -- 
|>         ---------  John Gloria - jpglori@pacbell.com	--------	
|>  		"You cannot depend on your eyes when your imagination
|> 	       is out of focus."   -     Mark Twain

	First the premise is not always true.  Not all Nikon AF lenses use
the motor that is in the camera body, not even all the more recent designs of the last decade.  All the latest generation Canon SLR equipment uses in-lens motors with one of two different technologies, linear or ultrasonic motors. The later is generally faster and more expensive. The Nikon bodies of the same vintage use several different coreless motor designs and electronic drivers with widely varying reponsiveness. There are a couple of new Nikon telephoto lenses with extremely fast built in coreless mot






ors.
	John's answer is such a gross generalization that it is wrong. Depending on the lens and motor design it may sometimes be true. There are lenses in both product lines that beat the competition on the equivalent body, when such an equivalence can be meaningfully established.  Usually this means comparing the F4 and EOS-1 focusing speeds on standard targets. Equal focal length lenses can have widely varying inertial masses for motors to work against depending on the number of elements, their groupings, and 






whether an internal focus design minimizes the moving mass. Usually a lens is designed first for optical properties and somewhere down the line AF speed is considered.  If AF speed were given a high priority, and motors were customized for the particular distribution of moving elements, it would in principle be possible to optimize the focussing speed. Canon has this as a design goal. It is very rarely done, and you pay top price for the design.  The most recent NIKON telephoto designs are a recognition of






 this fewer compromises approach. The advantage of a motor in body design is weight and cost.  You only need to buy one motor for a range of lenses, and you only have to carry one motor around and not N copies in your camera bag.  If this motor is of sufficiently high performance in conjuction with its circuits you win on efficiency, and lose on redundancy.  A quantum leap in motor design means replacing a camera body to upgrade the focusing speed of all your lenses.
	This is not to say that Nikon cameras and lenses are lighter, or that there are not other contributing factors and advantages for one design strategy over the other, but these are the most important reasons.  I do not recommend selecting current generation equipment based on one of these motor locations over the other.  Ease of use, the accessibilty of controls given the way you take pictures and use your equipment, the particular lens focal lengths you intend to use, and their combined utility, should be






 foremost. AF speeds will change tomorrow, and you can chase this rabbit incessantly without taking better pictures.

								Paul
Newsgroups: rec.photo