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100mm f/2 Canon lens, not focussing at distance

Stuart-MStuart-M Registered Users Posts: 157 Major grins
edited June 10, 2012 in Cameras
Hi,

I've started experiencing a strange problem with my Canon 100mm f/2 EF lens. It's fine most of the time, but will not autofocus on things more than around 15 feet away. Instead, the focus 'bounces up and down' without settling, I've recorded a short video of it doing this so you can see what I mean:

http://youtu.be/s6tYVluZY2s

Has anybody experienced a problem like this, and is it fixable without having to send the lens for a service?

Much appreciated.
Liverpool Wedding & Event Photographer

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    ziggy53ziggy53 Super Moderators Posts: 23,911 moderator
    edited June 7, 2012
    What happens if you switch the lens to manual focus? Does focus confirmation work in manual mode?

    Do you feel anything odd as you manually focus?

    Any rattle internal to the lens as you gently shake the lens?

    With the lens off the camera and the lens still in manual mode, look through the lens and see if the focus jumps at all as you manually rack the focus.
    ziggy53
    Moderator of the Cameras and Accessories forums
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    Stuart-MStuart-M Registered Users Posts: 157 Major grins
    edited June 7, 2012
    ziggy53 wrote: »
    What happens if you switch the lens to manual focus? Does focus confirmation work in manual mode?

    Do you feel anything odd as you manually focus?

    Any rattle internal to the lens as you gently shake the lens?

    With the lens off the camera and the lens still in manual mode, look through the lens and see if the focus jumps at all as you manually rack the focus.

    Hi Ziggy,

    Thanks for the reply. Just tried what you suggested, no sign of any rattle or anything strange when manually focussing. BTW, it happens on various cameras as well.

    Just found a thread about a similar sounding problem on a 17-85 that was apparently due to a faulty USM, so I guess it could be that?
    Liverpool Wedding & Event Photographer
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    ziggy53ziggy53 Super Moderators Posts: 23,911 moderator
    edited June 7, 2012
    Stuart-M wrote: »
    ... Just found a thread about a similar sounding problem on a 17-85 that was apparently due to a faulty USM, so I guess it could be that?

    The tests I had you perform could (potentially, maybe) help to rule out issues with the helicoid and guides. It could still be a few different things, but it does sound like a lens disassembly is going to be required.

    I recommend sending the lens to Canon service for repairs. I would not recommend continued use of the lens because the problem will likely get worse and potentially cause further damage.
    ziggy53
    Moderator of the Cameras and Accessories forums
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    Brett1000Brett1000 Registered Users Posts: 819 Major grins
    edited June 10, 2012
    Stuart-M wrote: »
    Hi,

    I've started experiencing a strange problem with my Canon 100mm f/2 EF lens. It's fine most of the time, but will not autofocus on things more than around 15 feet away. Instead, the focus 'bounces up and down' without settling, I've recorded a short video of it doing this so you can see what I mean:

    http://youtu.be/s6tYVluZY2s

    Has anybody experienced a problem like this, and is it fixable without having to send the lens for a service?

    Much appreciated.

    USM or something else, doesn't sound good. Unfortunately a trip to Canon for diagnosis
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