Autofocus problems with the 17-55mm f2.8 IS lens used with the Rebel XT (EOS 350D)

My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
body. Often the focus would end up being way in front of what I
thought I was focusing on... I mean WAY in front, by maybe 50 ft...
although it varied.

My other lenses autofocus well and dependably with the Rebel, but not
the 17-55mm f2.8 IS.

I sent the lens in to Canon for them to fix the autofocus under
warranty. But they returned the lens saying that it was working fine.

So I tried the lens out on a friend's 20D, and sure enough, the lens
works fine with the 20D... but not with my Rebel XT. The lens is still
in its warranty period, but the Rebel is not. Not sure what to do now.
Does anyone else have this problem with the 17-55mm f2.8 IS lens on
the Rebel? I'm wondering if it is a design fault or a sample issue.

KS

In the Canon software that came with the camera, does it show the focus
point that was used for the focus (obviously this will be a bit irrelevant
if you focused and then recomposed before taking the shot)?

What focus point settings are selected in camera? All focus points or just
one?


"King Sardon" <ksardon@fake.com> wrote in message
news:7o40e35tfe0cn4cvea6fnhfdmtgl3h3p5m@4ax.com...
> My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
> body. Often the focus would end up being way in front of what I
> thought I was focusing on... I mean WAY in front, by maybe 50 ft...
> although it varied.
>
> My other lenses autofocus well and dependably with the Rebel, but not
> the 17-55mm f2.8 IS.
>
> I sent the lens in to Canon for them to fix the autofocus under
> warranty. But they returned the lens saying that it was working fine.
>
> So I tried the lens out on a friend's 20D, and sure enough, the lens
> works fine with the 20D... but not with my Rebel XT. The lens is still
> in its warranty period, but the Rebel is not. Not sure what to do now.
> Does anyone else have this problem with the 17-55mm f2.8 IS lens on
> the Rebel? I'm wondering if it is a design fault or a sample issue.
>
> KS

I usually use just one focus point, and usually it is the central one.
The EXIF doesn't record this... not even whether AF or manual focus
was used.

I've done a bunch of tests using focus targets like road signs. They
are contrasty and flat and should serve this purpose well.

Oddly enough, all looks normal in the viewfinder, and I get focus
confirmation on that central point. But when I examine the results
later, the focus is off.

KS


On Thu, 6 Sep 2007 18:49:59 +0100, "Gino" <me@privacy.net> wrote:

>In the Canon software that came with the camera, does it show the focus
>point that was used for the focus (obviously this will be a bit irrelevant
>if you focused and then recomposed before taking the shot)?
>
>What focus point settings are selected in camera? All focus points or just
>one?
>
>
>"King Sardon" <ksardon@fake.com> wrote in message
>news:7o40e35tfe0cn4cvea6fnhfdmtgl3h3p5m@4ax.com.. .
>> My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
>> body. Often the focus would end up being way in front of what I
>> thought I was focusing on... I mean WAY in front, by maybe 50 ft...
>> although it varied.
>>
>> My other lenses autofocus well and dependably with the Rebel, but not
>> the 17-55mm f2.8 IS.
>>
>> I sent the lens in to Canon for them to fix the autofocus under
>> warranty. But they returned the lens saying that it was working fine.
>>
>> So I tried the lens out on a friend's 20D, and sure enough, the lens
>> works fine with the 20D... but not with my Rebel XT. The lens is still
>> in its warranty period, but the Rebel is not. Not sure what to do now.
>> Does anyone else have this problem with the 17-55mm f2.8 IS lens on
>> the Rebel? I'm wondering if it is a design fault or a sample issue.
>>
>> KS

On Thu, 06 Sep 2007 18:13:55 GMT, King Sardon <ksardon@fake.com>
mentioned:

>I usually use just one focus point, and usually it is the central one.
>The EXIF doesn't record this... not even whether AF or manual focus
>was used.
>
The ZoomBrowser software will show you which focus point was used.

Brian

On Thu, 06 Sep 2007 21:17:47 +0100, Brian
<briansnewsbox-01@yahoo.co.uk> wrote:

>On Thu, 06 Sep 2007 18:13:55 GMT, King Sardon <ksardon@fake.com>
>mentioned:
>
>>I usually use just one focus point, and usually it is the central one.
>>The EXIF doesn't record this... not even whether AF or manual focus
>>was used.
>>
>The ZoomBrowser software will show you which focus point was used.
>
>Brian

I see you are correct -- thanks.

KS

King Sardon <ksardon@fake.com> wrote:
> My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
> body.
> My other lenses autofocus well and dependably with the Rebel, but not
> the 17-55mm f2.8 IS.

> I sent the lens in to Canon for them to fix the autofocus under
> warranty. But they returned the lens saying that it was working fine.

Always send in lens AND body.
You have now experienced _why_.

> So I tried the lens out on a friend's 20D, and sure enough, the lens
> works fine with the 20D... but not with my Rebel XT. The lens is still
> in its warranty period, but the Rebel is not. Not sure what to do now.

Send in lens and body this time. Add shots where you demonstrate
the misfocussing.

> Does anyone else have this problem with the 17-55mm f2.8 IS lens on
> the Rebel? I'm wondering if it is a design fault or a sample issue.

Most certainly it is not a design fault, or RichA would have been
jabbering and drooling on it for years, the net would be full of
it ...

My guess is that the offset from true focus in your Rebel for
this lens is scrambled for some reason. Which is why you send
in the lens and the body, and images showing the problem.

-Wolfgang

On Sat, 8 Sep 2007 23:18:34 +0200, Wolfgang Weisselberg
<ozcvgtt02@sneakemail.com> wrote:

>King Sardon <ksardon@fake.com> wrote:
>> My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
>> body.
>> My other lenses autofocus well and dependably with the Rebel, but not
>> the 17-55mm f2.8 IS.
>
>> I sent the lens in to Canon for them to fix the autofocus under
>> warranty. But they returned the lens saying that it was working fine.
>
>Always send in lens AND body.
>You have now experienced _why_.
>
>> So I tried the lens out on a friend's 20D, and sure enough, the lens
>> works fine with the 20D... but not with my Rebel XT. The lens is still
>> in its warranty period, but the Rebel is not. Not sure what to do now.
>
>Send in lens and body this time. Add shots where you demonstrate
>the misfocussing.
>
>> Does anyone else have this problem with the 17-55mm f2.8 IS lens on
>> the Rebel? I'm wondering if it is a design fault or a sample issue.
>
>Most certainly it is not a design fault, or RichA would have been
>jabbering and drooling on it for years, the net would be full of
>it ...
>
>My guess is that the offset from true focus in your Rebel for
>this lens is scrambled for some reason. Which is why you send
>in the lens and the body, and images showing the problem.
>
>-Wolfgang

Thanks for your advice, which I followed early this morning. The store
where I bought the body has a very sagacious owner who somehow noticed
what was going on while I was discussing the problem (again) with one
of his sales guys. He came up, declared "this is a back focus
problem", "it's not the lens, it's not the body, it's the interaction
between them", "happens all the time, including with $10k cameras",
etc.

So body and lens are off to Canon for repairs under warranty.

KS

working fine.
>
> Always send in lens AND body.
> You have now experienced _why_.
>
sure
I sent my lens and camera in and am almost certain
they never checked the lens and camera together.
Anyway the same problem existed after I got them back.

On Sep 6, 11:14 am, King Sardon <ksar...@fake.com> wrote:
> My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
> body. Often the focus would end up being way in front of what I
> thought I was focusing on... I mean WAY in front, by maybe 50 ft...
> although it varied.
>
> My other lenses autofocus well and dependably with the Rebel, but not
> the 17-55mm f2.8 IS.
>
> I sent the lens in to Canon for them to fix the autofocus under
> warranty. But they returned the lens saying that it was working fine.
>
> So I tried the lens out on a friend's 20D, and sure enough, the lens
> works fine with the 20D... but not with my Rebel XT. The lens is still
> in its warranty period, but the Rebel is not. Not sure what to do now.
> Does anyone else have this problem with the 17-55mm f2.8 IS lens on
> the Rebel? I'm wondering if it is a design fault or a sample issue.
>
> KS

The lens is so heavy it is bending the body and contact is being lost
with the electrical lens contacts. Friend had the same issue with the
heavy Nikon 70-200mm f2.8 zoom and the Nikon D80. Both cameras have
plastic bodies.
No problems at all with the Nikon D200 (metal body).

On Sat, 08 Sep 2007 18:26:35 -0700, Rich <rander3127@gmail.com> wrote:

>On Sep 6, 11:14 am, King Sardon <ksar...@fake.com> wrote:
>> My 17-55mm f2.8 IS lens was not autofocusing well with my Rebel XT
>> body. Often the focus would end up being way in front of what I
>> thought I was focusing on... I mean WAY in front, by maybe 50 ft...
>> although it varied.
>>
>> My other lenses autofocus well and dependably with the Rebel, but not
>> the 17-55mm f2.8 IS.
>>
>> I sent the lens in to Canon for them to fix the autofocus under
>> warranty. But they returned the lens saying that it was working fine.
>>
>> So I tried the lens out on a friend's 20D, and sure enough, the lens
>> works fine with the 20D... but not with my Rebel XT. The lens is still
>> in its warranty period, but the Rebel is not. Not sure what to do now.
>> Does anyone else have this problem with the 17-55mm f2.8 IS lens on
>> the Rebel? I'm wondering if it is a design fault or a sample issue.
>>
>> KS
>
>The lens is so heavy it is bending the body and contact is being lost
>with the electrical lens contacts. Friend had the same issue with the
>heavy Nikon 70-200mm f2.8 zoom and the Nikon D80. Both cameras have
>plastic bodies.
>No problems at all with the Nikon D200 (metal body).

Hmm, I support the lens with my hand... also, as I have since
discovered, the problem occurs equally with manual focus.

KS