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  1. #1
    Join Date
    May 2019
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    Canon 85mm f1.8 AF jittery at longer focus points

    My gently used Canon EF 85mm f1.8 has suddenly started having focussing issues.

    -it focusses well up to about 4-5 m
    -beyond this, it does not lock focus, and chatters between two focus points, eg Infinity<=>5m about twice a second
    -manual focus is still perfect
    -make no difference if its on one-shot or servo focus mode
    -same behaviour on several camera bodies
    -AF/Manual switch is OK

    Has anybody had this issue? There is very little info available online. One article I have found suggest its the focus sensor at the front-end of the lens, but I'd like some opinions before I attempt to disassemble this lens, or pay to have it fixed.

  2. #2
    Join Date
    May 2007
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    Straylya - and love it.
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    Re: Canon 85mm f1.8 AF jittery at longer focus points

    ONCE all user shortcomings have been ruled out - AND - you are sure that it is the LENS and NOT the shooting conditions (i.e. low light, low contrast etc)

    THEN -

    My experience with Focus Hunting in Canon EF Lenses has always been caused by one of these three issues:

    1. Contacts - Electrical / Electronic - solution is to clean all exterior contacts and ensure battery/battery case have clean contacts and battery is fully charged, maybe dry or cracked joint to contacts inside lens on lens ribbon - the latter was a very popular issue with EF 24 to 105F/4L first release model.
    2. USM Motor is stuffed and needs replacement (not probable considering yours focuses OK at close distances)
    3. Dirty optical sensor - located inside the USM Motor, easy to get to IF you are adept at taking lenses to bits - it just needs a clean.

    WW

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