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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 16 Jun 2012 (Saturday) 08:16
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70-300 DO, cannot focus distant objects at 300 (70 OK)

 
bacma
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Joined Dec 2007
Location: New England, USA
     
Jun 16, 2012 08:16 |  #1

Hi Folks,

I have a 70-300 DO that I bought 2 years ago used with a known focus seeking problem. I sent it in to Canon in NJ and they fixed the seeking problem. I thoght is was pretty good. Only after looking at some pictures taken at distance did i discover that the lens was terrible at 300mm and distant objects (maybe a 15 pixel blur?). (sorry no examples) I did the testing at 1/1000s.

Summary :

at 70 AOK close and far at 1:1 good

at 300 close focus is good, distant focus is terrible.

I've tried manual focusing on either side of the auto focus infinity point but no improvement.

Is there a name for this defect? Is it fixable?

Anybody with similar experience?

Thanks!




  
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Skul
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Joined Oct 2011
Location: SE Texas
     
Jun 16, 2012 10:08 |  #2

That's a hard one to call without examples.
If the unit is still under the repair facilities warranty, they may address it for free.
Trouble being, if you didn't mention the problem in the first repair request, they may not.
Best of luck.




  
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rick_reno
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Jun 16, 2012 11:38 |  #3

sounds like an alignment problem in the glass, get it fixed.




  
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amfoto1
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Jun 16, 2012 13:39 |  #4

Before you go to too much trouble... Does the lens have a filter on it? If so, have you tried it without any filter?


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Wilt
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Jun 16, 2012 13:58 |  #5

photozone.de concludes, in its evaluation of this lens on 8MPixel APS-C body, "The performance is generally pretty even across the zoom range except maybe at the weakest spot which is surprisingly at 70mm f/4.5 rather than at the long end where we would typically expect this. " So your issues at 300mm sound atypical of expectations for this lens. OTOH, its resolution MTF values seem quite modest at about 1900 line-pairs per picture height, which is less than the 50mm f/1.8 and the considerably maligned original 17-85mm zoom, both tested on the same 8 Mpixel body.

Post some examples.


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macroimage
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Jun 16, 2012 19:59 |  #6

I have this lens and generally it is excellent. The only weak area is near the close focus limit at 300mm. At longer distances, it is very sharp. One of the things that makes this lens seem so sharp is that it has almost no chromatic aberration.

As others have said, if you have a filter on it, remove it. If that doesn't help, then get it serviced as there is clearly something wrong with it.


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70-300 DO, cannot focus distant objects at 300 (70 OK)
FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
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