danilo wrote:
Hi all,
I've personally tried only one USM lens, the canon 70-200 f/4 L one.
you know focus is not only QUITE (you don't hear nothing other than a
"zzz" - and sometimes only a "z") it's also faaaaast.
but this is not the best thing, as for many photographer the focus
speed w/o USM is just bearable.
the best thing, IMO, is the Full Time Manual Focus!!
(don't know how the pentax AF lens work, with the Tamron one I have
(17-34 2.8-4) I must switch the AF off every time I put it back in the
bag, otherwise I risk to break the AF system by accidentally turning
the focus ring doing it)
by,
Danilo.
The Pentax DA and D-FA lenses all have full-time manual focusing via a
clutch system. I'm given to understand that a couple of FA* lenses might
have it too, but I'm not sure. Pentax is the only company doing this
with screw-drive AF and it's a BIG win. Nikon could learn a thing or two
from Pentax here (As could Canon, I'm not paying $800CDN for a lens
without FTM, IS or no IS).
Note that not all USM lenses have this feature, the cheap micro-motor
type USM lenses lack it (Except the Canon 50mm f1.4 USM, which has a
Pentax-style clutch system in it to give FTM despite being micro-motor
USM).
-Adam
