Sylwester Pietrzyk wrote:
Adam Maas wrote on 12.01.06 15:39:
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.
These are still different lenses and 28-105 is undoubtely lighter with
exactly RF (Rear Focus). RF means that it only has to move rear elements,
which are very small in 3,5-4,5 zoom contrary to constant f2,8 zoom.
The 28-105 isn't RF, it's IF just like the Tamron. I have the lens in
front of me and checked, rear element's don't move, you can see the
elements behind the first group move when focusing. The elements
themselves might be heavier in the Tamron, but the overall build is much
lighter, and I'd assume that applies to whatever is holding the focusing
elements as well. The Canon lens in question is heavily built with a
metal barrel, especially for a 'consumer' zoom. You might be thinking of
the 28-105 f4-5.6 USM, which is a cheaply built lens and may be RF.
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.
Now you are talking about CAM module which has nothing to do with USM or no
USM drive. I didn't talk about AF locking speed, which depends on in-camera
AF sensors and AF microcomputer (and CAM-900 is very good here in low light
- contrary to Safox VIII), but about speed of lens drive. In this case
elements in Sigma were moved at similar speed whether it was driven by
Pentax screwdrive or by HSM motor.
Unfortunately the module does enter into the equation, unless you are
able to do a infinity-close focus test. Which is why I've made a point
to note what camera/sensor I've been using. I'm not sure of the speed of
the HSM motor in the Sigma's, it may not be up to the Canon or Nikon's.
Can't say, I haven't tried it.
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.
This particular AF-D lens is for sure not IF lens, it has to rotate big and
heavy front elements (filter 77 mm) during AF. Contrary to this AF-S is an
IF lens which has only small, light lens elements to move.
You are correct here, I forgot that all the non-AF-S 80-200's are non-IF
as well.
-Adam
