September 02, 2014, 05:25:09 AM

Author Topic: 600mm IS focus works well with close subjects and poorly with distant subjects.  (Read 1369 times)

Zenfren

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Is it possible for a lens to focus fine (high keeper rate) on close objects and have a difficult time focusing on distant objects? User error plays a huge role when focusing on distant objects but my question is mechanical.  Could a lens be defective in this way? :-[

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neuroanatomist

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Could a lens be defective in this way?

I bet it could, yes. 
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weixing

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Hi,
Is it possible for a lens to focus fine (high keeper rate) on close objects and have a difficult time focusing on distant objects? User error plays a huge role when focusing on distant objects but my question is mechanical.  Could a lens be defective in this way? :-[
    It's depend on the temperature you shoot. If the weather is hot, the further the object, the worst it is... this is basically due to rising of hot air (air mass is consider a lens element and when air is not stable, it's act as a irregular lenses) which make the image of far object blur especially obvious if you use a large diameter, long focal length lens (like the 600mm F4).

   Have a nice day.
« Last Edit: September 27, 2012, 10:15:07 AM by weixing »

bkorcel

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Yes but before you condemn the lens, perform a focus calibration with a tool like Reikan Focal.  It will not only make sure your lens focuses as good as it can at a long distance but will also show any issues with the focusing mechanism.  I typically calibrate with the target at about 30 meters.

You can post your test results here and you will get more opinions than you want on the condition of the lens.


Richard Lane

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Is it possible for a lens to focus fine (high keeper rate) on close objects and have a difficult time focusing on distant objects?

Other things to consider would be, the setting of the focus distance limiter switch on the lens, is focus search on or off in the camera, does it focus properly at long distances with manual focus?


bkorcel

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That brings up another interesting point.  You can do a quick check that's recommended by canon.  Find a high contrast target far away (more than 20 meters but farther if possible) and use Live View to focus on it at 10X magnification.  Then switch the camera to regular mode and focus on the same target.  The focus scale on top should not move at all.  Probably easier to do this on a tripod with a remote release.

Live view focuses using contrast comparison which is independent of what the AFMA value may be set in your camera.  So if the focus scale moves between one and the other focus modes, then you need to do a focus calibration.  If your camera doesn't support AFMA adjustments then you need to send the camera and lens back to Canon and have them match the lens to the camera...or upgrade to pro or semi pro camera where you can adjust the AFMA values.

Is it possible for a lens to focus fine (high keeper rate) on close objects and have a difficult time focusing on distant objects?

Other things to consider would be, the setting of the focus distance limiter switch on the lens, is focus search on or off in the camera, does it focus properly at long distances with manual focus?

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