----- Original Message -----
From: "Adam Maas" <[EMAIL PROTECTED]>
Pal, have you shot with a USM or AF-S lens? There's no comparison in AF
performance. USM absolutely blows screw-drive AF out of the water unless
you have either an ultra-light lens (like a 50mm) or one of the very few
cameras with a truly massive AF motor like the F5. I simply could not
believe the difference in AF performance between my old *istD and Tamron
28-75 f2.8 and the EOS 3 with a 28-105 f3.5-4.5 USM lens. The EOS was so
much faster I initially didn't believe my own eyes (Although some of that
likely has to do with having the same AF unit as the EOS-1D). USM is
needed in the Pentax line, badly.
I've tried the EOS-1v with the L 35-300 lens and this combo is as "slow" as
the MZ-S with the FA* 600/4.
I'm not denying that USM spins faster through the helicoid but when a
certain combination can follow virtually any subject you can point it at
with 4fps, what then is the point with faster AF unless you shoot 8fps?
Incidentally, Andy Rouse claims that the AF of the Pentax 645NII, which uses
SAFOX V, with the FA* 300/4 give just as many keepers as the EOS-1v. USM is
needed for marketing reasons. Spinnning fast through the helicoid with lens
caps on gives bragging rights in brochures...
I don't think the post you were responding to was talking about large
aperture zooms but rather fast AF zooms. Large aperture zooms have bigger
glass and are thus more difficult to drive for AF, on the other hand, tehy
do gather more light and usually have better contrast, which helps the AF
unit.
No. Large aperture zooms have large front elements that are not used in
focusing. Besides, most such lenses has inner focussing as well making them
easier to focus than, say, a consumer lens where whole lens tubes + glass
need to be moved in order to focus. . In fact, the 77 Limited is "harder"
job on the AF system than a super telephoto IF lens.
- Re: new AF system soon (when D2 arrives)? Pål Jensen
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