Any of the zoom lenses with a focusing scale inside a window
on the lens is guaranteed to be - is the term "parfocal" ?
If the lens in question did not maintain focus when it zoomed, the
focus distance scale would move when zooming. I have not seen a single
Canon lens do this.
I am surprised that you say the 50-200 fails - I have access to one, I
will
also check it out... But I repeat, almost all modern zoom lenses do not
adjust focus distance with zooming.
On 11 Jun 2009, at 4:57 PM, C.H.Ling wrote:
> 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
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