I have not disassembly any Canyon lenses but I bet all of them has
mechanical calibration. I found calibration point for all the lenses I have
disassembled, calibration is a necessary procedure for all MF lenses, I
doubt it is not for AF. I have seen spacers (thin rings) of different
thickness put around the rear mounting of AF lenses, they are for adjusting
the distance between the whole lens to the film plan.
For AF lenses, if you never tried to use MF and zoom without re-adjust the
focus you will never know whether your lens can maintain focus or not since
every time you 'zoom and shoot' the AF re-focus again.
All lenses were calibrated before ex-factory and they are accurate to a
certain extend, but with live view you see what is real accuracy. Since I
acquired all my lenses used and many of them are over twenty years old so
re-calibration is required due to age (use) or they have been disassembled
for cleaning by the others and without a good calibration. Among all lenses
I have purchased some do work accurate enough to skip this re-calibration.
The story I heard about purchase and sell to get the best lens is just the
famous 70-200/2.8 IS L, for cheap lenses it does not worth the effort. I'm
trying to do the same for Tamron AF24-135 as I like this range and the
quality (when it is well calibrated) but I will buy used one, unfortunately
it does not appear very frequently. The last one I bought was having very
uneven performance from left to right but I sold it at no loss. This kind of
problem is seldom seen with MF lenses.
I just re-checked the test shots I done for my friend's 17-40 L, there is
also a hint for the above problem:
http://www.accura.com.hk/temp/IMG_1759.JPG
C.H.Ling
----- Original Message -----
From: "Dawid Loubser"
> Well now, that depends on which Canon lenses you buy - from personal
> experience, every L-series lens I have used does not at all depend
> on "calibration" as to whether it is parfocal or not - it all boils down
> to mechanical engineering and precise metal helicoids. I know this is
> an Olympus list (and the fact that I sold all my Canon EF gear and
> replaced
> it with OM gear gives me, I think, a right to comment on the relative
> merits of both systems) but there is no denying that most of the L-
> series lenses
> are optically and mechanically absolutely superb.
>
> This is a completely different story to the more "modern" focus-by-wire
> designs the new Olympus lenses have which may depend on calibration,
> but the
> Canon lenses (except the few focus-by-wire lenses from the late 80s) are
> all fully mechanical.
>
> On the other hand, there is no denying that the consumer-grade canon
> lenses
> are built like toys, whereas cheap Olympus lenses are built a bit
> better (but
> not much).
>
>
> On 11 Jun 2009, at 6:06 PM, C.H.Ling wrote:
>
>> A slower lens will help a little but this is not the key. Fine
>> calibration
>> is required if you wanted to ensure no focus shift during zooming. I
>> calibrated many Zuiko zooms (and also the two Tamrons I just
>> acquired) in
>> order to ensure the focus does not change during zooming, this is more
>> critical for the wide zooms.
>>
>> I suspected the modern AF lenses are more difficult to ensure for this
>> aspect as the AF mechanism (lens element group) need some space for
>> movement
>> (can't be too tight). I see some lenses even have different
>> sharpness from
>> left to right side, this including a Tamron 28-300mm, DZ 11-22mm,
>> Tarmon
>> 24-135mm, DZ 14-42mm. I also heard some stories about the poor quality
>> control/standard of Canyon, people keep purchasing the lens until
>> they found
>> a best one, the rest just sell it out.
>>
>> C.H.Ling
--
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