I have different experience, the Canyon 28-135 IS I once owned does not
maintain focus (very serious, more than 4mm on the scale from 28 to 135), I
send it to Canyon repair center and they spent two weeks to tell me this is
normal. I also had tried a Sigma 17-35 it also can't maintain focus, you
simply can't use the distance scale. The Tamron AF 70-300 was better, only
sligthly off.
I don't have experience on other Canyon, I had the 17-40 but without live
view at that time and with the lousy focusing scale I don't know if it can
maintain focus or not.
For Olympus, after getting the E-3 with live view, I found the following:
14-45 - ok
40-150 3.5-4.5- ok
11-22 - failed
50-200 - failed
C.H.Ling
----- Original Message -----
From: "Dawid Loubser"
> Ken, my experience does not agree with you on this point -
> I have used about a dozen Canon EF-series zoom lenses, and every
> single last one of them, from the cheap kit lenses, to the monstrously
> expensive 28-300mm L IS USM, maintained a constant focus distance
> regardless of focal length.
>
> On 11 Jun 2009, at 4:11 PM, Ken Norton wrote:
>> Most modern lenses are zoom lenses. Most zooms now are a form of
>> "Varifocal"
>> design. As such, you cannot zoom in on a subject, manually focus (or
>> focus
>> lock) and zoom back out and expect the focus to stay put.
--
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