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Archive 2013 · Lens not auto focusing; repair or recalibrate
  
 
kkennardis
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p.1 #1 · p.1 #1 · Lens not auto focusing; repair or recalibrate


I am considering sending out a EF 180mm f/3.5L macro USM for repair.. It will not auto focus, it just goes back and forth repeatedly. I have ruled out dirt on the contacts, changed the settings from MF and back to AF etc. I have changed the .48m to infinity to 1.5m to infinity and still have the same issue. I first noticed the issue last summer and now that i am considering putting up for sale since I do not put the lens to much use anymore. The lens is sharp as a tack so I may also just consider giving a fair "as is" price on it and declare the auto focus issue in the sale since auto focus is hardly used in macro work anyway.
I want to get a ball park idea what canon may charge for repair and also I wonder if I could just get away with sending it out for a cleaning/recalibrating and have it come back repaired. If anyone out there has some insite on this through past experience with Canon I would be gratefull.

Thank you in advance for any insite you can provide.

Ken




Jan 20, 2013 at 09:27 PM
jcolwell
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p.1 #2 · p.1 #2 · Lens not auto focusing; repair or recalibrate


Is the aperture stopped down when it's off the camera? If no, it's probably the USM.


Jan 20, 2013 at 09:44 PM
kkennardis
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p.1 #3 · p.1 #3 · Lens not auto focusing; repair or recalibrate


Not sure, when I take it off the camera the focus is past infinity both times. I even tried again, and i manualy turned the focus ring to focus much closer, then it goes back and forth then utltimately ends up past infinity. Is that what you mean?

Ken



Jan 20, 2013 at 09:56 PM
BrianO
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p.1 #4 · p.1 #4 · Lens not auto focusing; repair or recalibrate


kkennardis wrote:
Not sure, when I take it off the camera the focus is past infinity both times. I even tried again, and i manualy turned the focus ring to focus much closer, then it goes back and forth then utltimately ends up past infinity. Is that what you mean?


Nope. The aperture is the hole in the iris through which light travels. When you change from -- for example -- f/4 to f/5.6 the aperture gets smaller.

AF requires a fair amount of light to work, and so modern cameras are designed so that the aperture is at its widest during focusing and then closes down to the shooting aperture when the shutter is released.

If the aperture is stuck in a small position there won't be enough light reaching the AF sensor, so it will "hunt," trying but unable to lock focus.

One way to tell if your aperture is stopped down is to set the camera for a smaller-than-maximum aperture (smaller than f/3.5 on your camera) and -- while looking through the viewfinder -- press the Depth of Field preview button. You should see the image in the VF get a little darker. If not, it may be stuck at a smaller aperture than the one you set. Keep repeating the experiment at progressively smaller apertures until (if) you can see a change in the VF to know where it's sticking.


Edited on Jan 21, 2013 at 10:05 PM · View previous versions



Jan 21, 2013 at 02:51 AM
kkennardis
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p.1 #5 · p.1 #5 · Lens not auto focusing; repair or recalibrate


I did press the dof preview button but did not progressively go through each apertures. I will try that out today thanks.


Jan 21, 2013 at 12:13 PM





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