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I have a Canon T3i (600d) and two lenses: EF-S 18-135mm and EF 50mm f/1.8.

While working with manual focus, I can shoot out of focus (on purpose) with the 18-135 (as expected). But with the EF 50mm, it will only trigger when the subject is in focus, otherwise it tries to "focus" (I hear and feel the focus motor, but as the focus-ring is deattached, nothing happens).

It's weird, it's supposed to let me shoot at any focus (as with the 18-135). I don't think it's a camera problem.

Is it a problem or a specification of the EF 50mm f/1.8? It works perfectly with autofocus.

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I'd take it back in to get it serviced. –  Chinmay Kanchi Apr 12 '13 at 23:19
    
Yes, I thought. The weird thing is that in AF, it works OK. The fact that it shoots only when it's in focus makes me think in an software/controller issue, not in a hardware one :-/ –  Marcelo Pascual Apr 13 '13 at 0:40

1 Answer 1

In order to fire the shutter when any of the variants of the EF 50mm f/1.8 is out of focus, the switch on the lens must be set to M (manual) rather than AF (auto focus). Attempting to manually focus those lenses with AF engaged can damage the focusing motor and mechanism. If the motor is still trying to engage when the lens is set to M it needs to be serviced.

There are two variants of the Canon 18-135 lens. The older EF 18-135mm f/3.5-5.6 IS behaves the same as the 50mm f/1.8 series with regard to focus. You should not attempt to manually focus the lens when the switch is set to AF. For the newer EF 18-135mm f/2.5-5.6 IS STM, Full Time Manual focusing (manual focusing when the switch is set to AF) is available, but only after AF completes in One Shot mode with the shutter release remaining half-pressed. I was under the impression this only worked with the newer T4i and newer bodies, but based on your experience described in your question the T3i is compatible with this feature as well.

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Yes, of course the focus switch is set to Manual (for both lens) :) –  Marcelo Pascual Apr 13 '13 at 2:55
    
I've searched to see if there are any widespread reports of the firmware on the T3i causing this behavior. I can't find any. The first update of the T3i firmware following its release did have to do with a focus issue related to a specific shoe mounted flash, but that has been a while back. Do you know anyone else with an EOS camera that you can try the lens on to see if the focus motor engages when the switch is set to M? –  Michael Clark Apr 13 '13 at 5:42
    
Good idea, I'll try to reach someone with an EOS camera and test the lens. I'm almost sure that the problem is on the lens. Thanks for your reply :) –  Marcelo Pascual Apr 14 '13 at 22:24

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