Sylwester Pietrzyk wrote:
Adam Maas wrote on 12.01.06 2:38:
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.
You were comparing AF performance of heavy optics of metal built non-IF f2.8
lens to light, plastic, IF-equipped f3.5-4-5 lens... In 2004 when we meet
with Dario we compared AF speed of two identical lenses in good light -
Sigma EX 70-200/2,8 - one mounted on Dario's *istD, naturally screwdriven
AF, second one with HSM motor and mounted to Nikon D70. I can assure you
that there was no significant difference in AF speed at all, I've got even
feeling that *istD was somewhat faster, but I could be under some influence
of AF motor sound in *istD :-) I hope Dario will read this and confirm my
observations. The conclusion is, that if you have two mechanically identical
lenses, than there will be little difference between USM and good classic
drive. Two main advantages of USM are its quietness and possibility to
manual tweak of focus (FTM - this is now available in new Pentax lenses as
QSF too).
The Tamron 28-75 is a light, IF equipped semi-pro zoom. The Canon 28-105
is a light, IF equipped USM consumer zoom. The Canon is the heavier
build, with more metal. They weigh about the same and should perform
similarily, actually, I'd expect the 28-75 to be faster, given it's
better contrast and larger maximum aperture and really light build.
BTW, the D70's AF unit is not a terribly good performer. I've used the
Multi-CAM900 in the past (used to own a F65 with the same unit) and I'd
say that particular sensor is distinctly inferior to the SAFOX VIII in
the D.
Having compared the 80-200 f2.8 AF-S and AF-D on the F90x (Which has
both a more powerful AF motor and a more sensitive sensor than the D70,
I distinctly saw a difference in performance in the AF-S versions favour.
-Adam
