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.
> 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. > 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. -- Balance is the ultimate good... Best Regards Sylwek
