EF 135 F2 L hunting around focus point

[Israeld09]

My 135mm L was starting to separate right behind the focus point, I opened it and replaced two screws that hold the Rear element in place, but now after reassembly it has a hard time confirming autofocus. It will lock onto the subject and then rack back and forth, sometimes confirming after several seconds or not at all. Manual focus works fine and I do get a focus confirm light and beep if the AF eventually does find its subject. I’ve even replaced the entire focus tube (rotor, stator, spring , compression ring, and the two ribbon cables that come with it). Exact same symptoms. I’ve cleaned the encoded glass and focus sensors as well, little to no change”.  I’m thinking I don’t have something aligned properly.  I’ve also tried the lens on two cameras. 

[Anonymous]

Sounds like it needs to be sent to Canon for repair.

[jrhoffman75]

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@Anonymous wrote:

Sounds like it needs to be sent to Canon for repair.

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Agree. And be sure you tell them exactly what you did. It will help them in diagnosing and rectifying your problems. 

[TifeVep]

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@Israeld09 wrote:

My 135mm L was starting to separate right behind the focus point, I opened it and replaced two screws that hold the Rear element in place, but now after reassembly it has a hard time confirming autofocus. It will lock onto the subject and then rack back and forth, sometimes confirming after several seconds or not at all. Manual focus works fine and I do get a focus confirm light and beep if the AF eventually does find its subject. I’ve even replaced the entire focus tube (rotor, stator, spring , compression ring, and the two ribbon cables that come with it). Exact same symptoms. I’ve cleaned the encoded glass and focus sensors as well, little to no change”.  I’m thinking I don’t have something aligned properly.  I’ve also tried the lens on two cameras. 

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Absolutely agree. It's essential to communicate precisely what actions you took. This detailed information will significantly assist them in diagnosing and effectively addressing any issues you encountered.

[ebiggs1]

Keep in mind the lens does not focus. Yes it move back and forth but the camera tells it when it is in focus. The lens doesn't know whether it is or isn't.

If you send it to Canon and tell them what you did and I absolutely think you should, they may either refuse to repair it or it will be a very costly service. They won't repair it if they can not guarantee you it is in perfect working order. If I was the service tech I wouldn't touch it.

[wq9nsc]

I agree with Ernie that there is a very good chance that Canon isn't going to touch this given an attempted customer repair.  YOU may not have caused any additional issues but additional issues are often caused by attempted customer repair and for that reason many service organizations will refuse to repair because of the risk of complex problems and resultant high cost.

If Canon refuses, you may have better luck with a third party repair house but they will likely charge a high deposit fee payable in advance with potential additional charges later.  The EF 135 f2 is a nice lens and a lot of copies were sold.  You can easily find a used one in nice operating condition in the $600 range and I would strongly consider that with respect to getting your current lens repaired.

Rodger

[Tintype_18]

Question: Were the replacement screws the same at the original?

[shadowsports]

Expert consensus in this thread. 

I cannot reiterate enough what has already been said here. Even if you are an electrical engineer, this is/was a job for a professional.  Whether you choose repair or replacement, stop now and get the lens into the hands of someone qualified to repair it.  You'll get your lens back in under 2 weeks and it will work like it did when purchased.  I'm late to this thread, but I hope it works out for you.