Canon 35mm f/1.4 L AF Problem?

Hi,

I have a Canon EF 35mm f/1.4 L that is old and very used. Sometimes the autofocus doesn’t want to work. When I take the lens off and put it on again it sometimes starts working again. When I switch to manual I can take pictures.

Do you have any tips on how I can check what’s wrong?

I think I would start by gathering a bit more data on what makes the AF start working again when it quits. For instance, does power cycling the camera do it? Flipping the AF/MF switch? As it stands, it sounds reasonable that it's a contacts issue but maybe you'll find there's more to it.

Let that info guide you as to whether it's something you can fix yourself or something you need to send the lens out for. I currently have a lens at Midwest Camera for a tune-up and I bet they could give you good advice on getting that lens working right again.

Please detail for us what the autofocus is doing. Knowing how it is not working helps diagnosing problems.

Thank you guys. I noticed earlier that the lens is loose in the middle, like it’s coming loose into two parts almost. When I saw this I taped it together with electrical tape. By doing this, the manual focus ring was disabled. I noticed now that the tape let go slightly, so that the lens had come apart 1 or 2 mm. I took off the tape and pushed it together and re taped it, and now the auto focus works again. I haven’t tried it so much yet to be sure, but maybe this was the whole problem.

It is quite easy for the manual focus ring to disengage the AF motor if parts of the body are loose. With what you said, I would worry about screws coming loose and possibly jamming the focusing. Since this is a prime, it is easier to take apart than a zoom. You will need a good set of JIS screwdrivers, a parts catalog for the lens and some knowledge of removing connectors properly. I can't recall but I think you will also need a lens spanner to take off the front ring to get access to the other side of the lens (disassembly from the rear only takes you so far and then you have to start at the front). Check the front filter ring to make sure there are no dents as this would hinder getting access. I would start from the rear since it will be much easier and see if that remedies the problem.

You should be able to re-tighten it and get more life out of it. You won't need to mess with any glass elements nor take off any parts like the AF motor. Also don't over tighten the screws, just snug them up. That way you don't risk damaging the screw heads which is the kiss of death for the lens. Lastly when loosening the screws, make sure to put force into the screw to keep the screwdriver seated into the screw as you turn it slowly to make sure it is loosening, again you don't want to go too fast and ruin the screw head.

Let me know if you need further details.