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EOS AF lens that doesn't AF

 
 
eug k
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      04-05-2004

hi,

I sold a 28-105mm f3.5 lens recently, and the buyer says it
doesn't autofocus.

In his words:

"I used the lens this weekend to take pictures from a
performance. It appears that the camera works well with
short distances, but when the object is at a a distance
of more than 15 meters the automatic focussing keeps
going in and out , it does not find a proper position. This
I think is a malfuction from the lens.The macro also palys up."


I further clarified that he can get a good focus if he focuses
manually. In AF mode, the lens just seeks from end to end.
Isn't AF handled by the camera and not the lens, searching
for best contrast? It's an EOS300D.


thanks



--

 
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Randall Ainsworth
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Posts: n/a
 
      04-05-2004
> "I used the lens this weekend to take pictures from a
> performance. It appears that the camera works well with
> short distances, but when the object is at a a distance
> of more than 15 meters the automatic focussing keeps
> going in and out , it does not find a proper position. This
> I think is a malfuction from the lens.The macro also palys up."


What kind of performance. Nobody's autofocus works well in low light
conditions.
 
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cole
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      04-05-2004
Well I don't know how a macro can "play up" - that's just a close focusing
distance


 
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Dave
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      04-05-2004
I have the Digital Rebel (300D) and I experience was he described
with every lens that I use if there isn't enough available light. I would
suggest that the auto focus be tested in a situation with plenty of light.
i.e.@ ISO 100 & F8, shutter speed would be faster then 1/60th.
-Dave

"eug k" <(E-Mail Removed)> wrote in message
news:c4sjoh$p6k$(E-Mail Removed)...
>
> hi,
>
> I sold a 28-105mm f3.5 lens recently, and the buyer says it
> doesn't autofocus.
>
> In his words:
>
> "I used the lens this weekend to take pictures from a
> performance. It appears that the camera works well with
> short distances, but when the object is at a a distance
> of more than 15 meters the automatic focussing keeps
> going in and out , it does not find a proper position. This
> I think is a malfuction from the lens.The macro also palys up."
>
>
> I further clarified that he can get a good focus if he focuses
> manually. In AF mode, the lens just seeks from end to end.
> Isn't AF handled by the camera and not the lens, searching
> for best contrast? It's an EOS300D.
>
>
> thanks
>
>
>
> --
>



 
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[BnH]
Guest
Posts: n/a
 
      04-05-2004
Eugene,

It does happen.
Last time I bought a used Nikkor 24-85 f/ 2.8-4, it does not want to focus
in 3 of my bodies.
Somehow the problem it does not focus @ infinity .. the focus always runs.
There is a fix for it .. but might be costly [CLA-ing them for quick fix]
Too bad it has a dent in the filter thread, if not I dun mind sending it to
maxwell to be fixed.
Hell it was a sharp lens

=bob=




"eug k" <(E-Mail Removed)> wrote in message
news:c4sjoh$p6k$(E-Mail Removed)...
>
> hi,
>
> I sold a 28-105mm f3.5 lens recently, and the buyer says it
> doesn't autofocus.
>
> In his words:
>
> "I used the lens this weekend to take pictures from a
> performance. It appears that the camera works well with
> short distances, but when the object is at a a distance
> of more than 15 meters the automatic focussing keeps
> going in and out , it does not find a proper position. This
> I think is a malfuction from the lens.The macro also palys up."
>
>
> I further clarified that he can get a good focus if he focuses
> manually. In AF mode, the lens just seeks from end to end.
> Isn't AF handled by the camera and not the lens, searching
> for best contrast? It's an EOS300D.
>
>
> thanks
>
>
>
> --
>



 
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Quaoar
Guest
Posts: n/a
 
      04-06-2004
eug k wrote:
> hi,
>
> I sold a 28-105mm f3.5 lens recently, and the buyer says it
> doesn't autofocus.
>
> In his words:
>
> "I used the lens this weekend to take pictures from a
> performance. It appears that the camera works well with
> short distances, but when the object is at a a distance
> of more than 15 meters the automatic focussing keeps
> going in and out , it does not find a proper position. This
> I think is a malfuction from the lens.The macro also palys up."
>
>
> I further clarified that he can get a good focus if he focuses
> manually. In AF mode, the lens just seeks from end to end.
> Isn't AF handled by the camera and not the lens, searching
> for best contrast? It's an EOS300D.
>
>
> thanks


It is the camera that handles the control and evaluation of the
autofocus and drives the lens. EOS lenses have never been reliable
focusing in low light, against textures with little direct reflectivity
such as cat and dog fur, some tree leaves, etc. With low light or low
reflectivity, the change in the control point is flat and the control
algorith fails to converge and the lens hunts. Canon has not hidden
these characteristics of the lenses; every user manual I have (not
anything recent) discusses the limitations. IMO, it is not a defect
since manual focus is a viable alternative. The auto/manual focus
switch becomes an element of using the lenses after even a little use.

Your customer should give the lens a real workout; it costs nothing but
time to test focus against a variety of targets in different lighting.
Again, the EOS control algorithm is built into the camera; inability to
focus is a camera problem unless the lens is broken, which should be
readily obvious if it is.

Q


 
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jean
Guest
Posts: n/a
 
      04-06-2004
Also, if you let the camera decide which focus point to use it will be more
"confused" in low light situations. Tell him to select only the center AF
point, it shoud focus much better and faster.

Jean

"Quaoar" <(E-Mail Removed)> a écrit dans le message de
news:(E-Mail Removed)...
> eug k wrote:
> > hi,
> >
> > I sold a 28-105mm f3.5 lens recently, and the buyer says it
> > doesn't autofocus.
> >
> > In his words:
> >
> > "I used the lens this weekend to take pictures from a
> > performance. It appears that the camera works well with
> > short distances, but when the object is at a a distance
> > of more than 15 meters the automatic focussing keeps
> > going in and out , it does not find a proper position. This
> > I think is a malfuction from the lens.The macro also palys up."
> >
> >
> > I further clarified that he can get a good focus if he focuses
> > manually. In AF mode, the lens just seeks from end to end.
> > Isn't AF handled by the camera and not the lens, searching
> > for best contrast? It's an EOS300D.
> >
> >
> > thanks

>
> It is the camera that handles the control and evaluation of the
> autofocus and drives the lens. EOS lenses have never been reliable
> focusing in low light, against textures with little direct reflectivity
> such as cat and dog fur, some tree leaves, etc. With low light or low
> reflectivity, the change in the control point is flat and the control
> algorith fails to converge and the lens hunts. Canon has not hidden
> these characteristics of the lenses; every user manual I have (not
> anything recent) discusses the limitations. IMO, it is not a defect
> since manual focus is a viable alternative. The auto/manual focus
> switch becomes an element of using the lenses after even a little use.
>
> Your customer should give the lens a real workout; it costs nothing but
> time to test focus against a variety of targets in different lighting.
> Again, the EOS control algorithm is built into the camera; inability to
> focus is a camera problem unless the lens is broken, which should be
> readily obvious if it is.
>
> Q
>
>



 
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Cello
Guest
Posts: n/a
 
      04-06-2004
Have your buyer change his settings to a single focus point. This made all
the difference for me on my 300D when shooting in low-light conditions.


"eug k" <(E-Mail Removed)> wrote in message
news:c4sjoh$p6k$(E-Mail Removed)...
>
> hi,
>
> I sold a 28-105mm f3.5 lens recently, and the buyer says it
> doesn't autofocus.
>
> In his words:
>
> "I used the lens this weekend to take pictures from a
> performance. It appears that the camera works well with
> short distances, but when the object is at a a distance
> of more than 15 meters the automatic focussing keeps
> going in and out , it does not find a proper position. This
> I think is a malfuction from the lens.The macro also palys up."
>
>
> I further clarified that he can get a good focus if he focuses
> manually. In AF mode, the lens just seeks from end to end.
> Isn't AF handled by the camera and not the lens, searching
> for best contrast? It's an EOS300D.
>
>
> thanks
>
>
>
> --
>



 
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Paul J Gans
Guest
Posts: n/a
 
      04-08-2004
In rec.photo.digital Dave <(E-Mail Removed)> wrote:
>I have the Digital Rebel (300D) and I experience was he described
>with every lens that I use if there isn't enough available light. I would
>suggest that the auto focus be tested in a situation with plenty of light.
>i.e.@ ISO 100 & F8, shutter speed would be faster then 1/60th.
>-Dave


The ability to manually focus in such situations is one of the
reasons for buying a camera such as the 300D.

---- Paul J. Gans
 
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John Navas
Guest
Posts: n/a
 
      04-08-2004
[POSTED TO rec.photo.digital - REPLY ON USENET PLEASE]

In <c53j0i$r66$(E-Mail Removed)> on Thu, 8 Apr 2004 13:10:42 +0000 (UTC),
Paul J Gans <(E-Mail Removed)> wrote:

>In rec.photo.digital Dave <(E-Mail Removed)> wrote:
>>I have the Digital Rebel (300D) and I experience was he described
>>with every lens that I use if there isn't enough available light. I would
>>suggest that the auto focus be tested in a situation with plenty of light.
>>i.e.@ ISO 100 & F8, shutter speed would be faster then 1/60th.

>
>The ability to manually focus in such situations is one of the
>reasons for buying a camera such as the 300D.


Lots of lesser cameras can be manually focused.

--
Best regards,
John Navas
[PLEASE NOTE: Ads belong *only* in rec.photo.marketplace.digital, as per
<http://bobatkins.photo.net/info/charter.htm> <http://rpdfaq.50megs.com/>]
 
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