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When looking for lens bargains on eBay, I often come across lenses that have something like this in their description:

Lens will not focus automatically or manually. For parts or repair only.

Such lenses seem to be surprisingly common, every time I check eBay, there are 10 or so Canon lenses listed that have this problem.

What could be wrong internally with such lenses? And how easy would it be for a good third-party shop to fix? Some of these lenses are ridiculous bargains (I wonder why :P), and I can't help but be tempted to try.

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Will be interesting to read an answer to this, if there's any experience in broken lens repairs behind the answer. Otherwise it will turn out only uncertainties and speculation. –  Esa Paulasto Apr 17 '13 at 21:48
1  
Depends, there are a lot of very experienced photographers here that might want to chime in. –  Chinmay Kanchi Apr 17 '13 at 22:01

3 Answers 3

up vote 2 down vote accepted

What could be wrong internally with such lenses? And how easy would it be for a good third-party shop to fix? Some of these lenses are ridiculous bargains (I wonder why :P), and I can't help but be tempted to try.

Common things that break with lenses:

  • a belt or loop is used to couple focus elements, the belt or loop has slipped off and thus no longer couples, resulting in loss of AF and/or loss of MF. This can be corrected by replacing the belt or re-engaging the belt onto the respective places.

  • a lens element has shifted sufficiently to prevent proper focusing. Determine the element that has shifted out of focus and re-set it. Having a manual or a VERY adventurous spirit helps.

  • a component has become jammed. a tiny screw, a bit of broken metal, someone dropping something into a gap between the rear lens element and the lens body... dissassemble and remove the problem item, reassemble.

  • focus components sticking... grease/oil/etc. requires cleaning... after a complete strip down of the lens.

There are quite a few causes for lens AF/MF failure. Sometimes, it's something simple and can be easily fixed, netting you a cheap and usable lens. Other times, it is something that looks easy, but turns out to be pretty severe... in which case, you've spent some monies on a nice paperweight.

So long as you view the money you spend on the "as-is" lens as disposable and not an investment, sure, go for it. You can even find maintenance manuals for lenses if you search for them.

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A third party shop should be able to fix 2, 3 and 4 fairly easily, and maybe 1 (if it doesn't require specific parts)? If parts are required, I assume it will be nearly as expensive as manufacturer service, which in the case of Canon, can be nearly as much as a new lens... –  Chinmay Kanchi Apr 17 '13 at 22:52
    
Very true. Yes, sending the lens off to get fixed, can be excessively expensive, since the lens is most likely not under any coverage anymore. So you foot the whole bill. :( I've got a small drawer full of disassembled lenses that I've bought in various forms and shapes. Some for spare parts, others to test changing mounts, and still others, just to learn how the lens works. But yeah, unless you have the knowledge and tools/materials to fix it yourself, sending to the service centers can be expensive. –  Wing Tang Wong Apr 17 '13 at 22:58
  1. Some lenses implement fly-by-wire focusing, using a motor for both manual focus AF. Certain high end Canon lenses like the 50 f/1.0, 85 f/1.2 and 200 f/1.8 use this approach. This means if the motor fails you can no longer manually focus. You can usually get a spare motor from a donor lens with different defect. Any competent repair centre of skilled amateur could replace the motor.

  2. Most lenses use a helicoid to convert rotational motion of the focus ring into linear motion of the focussing group of lenses. A lack of lubrication, corrosion or a foreign object jamming the helicoid could prevent both manual and autofocus. This should be relatively easy to fix for anyone competent to dissemble a lens and put it back together. Alternatively eh lens barrel of helicoid could be bent or deformed in some way. This would be a much harder fix.

  3. Some lenses *cough* Canon 50 f/1.4 *cough* use a delicate clutch mechanism to enable full time manual focus which is very prone to breakage. I don't know what's involved in a repair, but there are enough examples of this floating about that someone will have figured it out.

  4. Other optical defects (e.g. lose or missing elements in the rear, broken floating element mechanisms) could prevent a focussed image being formed at any distance. Technically this is not a failure of the focus system. I wouldn't go near a lens if this was the case.

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Lenses are usually high tech pieces of technology that are made out of a lot of different types of components; optic-related components, electrical components, mechanical components, etc. The photography sector is nowadays a very big sector and firms have to produce 'better' (more zoom, fast autofocus, image stabilizer, big aperture, etc.) lenses to maintain a good position in the business.

BUT, at the same time, those lenses usually do not have to be very big, heavy and (probably mainly) expensive, at least not for the majority of the targeted audience; normal people with a photography hobby.

Lenses usually are already a compromise between different aspects like durability, image quality, price, weight, etc. But due to the constraints (lenses have to be light, small, cheap) some parts of the lens cannot be built with the ‘ideal’ specifications: strong, durable, quality feeling, etc.; the strength of certain components could be less than ideal, the connections (with glue, welding, screws, whatever) between parts could be less strong or durable, the internal wear could become an issue after time, etc.

So, lenses in general are already quite fragile instruments, compared to furniture and cutlery for example. When a lens is used intensively the wear increases and besides that, after a period of time the chance of breaking or jamming just increases. Abusing lenses/ focus mechanisms (turning when it is not possible, very wild turning) will make the probability of failure higher. Dropping a lens (or letting the front end of the lens hit other objects) is for the same reason quite dangerous. On internet forums and youtube for example there are a lot of individuals who give tutorials about fixing specific issues; tightening screws inside a lens are an example of one of those issues(tamron 17-50) ,but tutorials of fixing broken autofocus mechanisms are there as well. After searching a bit on the internet I have found some opinions about repairing like:

I don't think anyone without the proper training and tools have ever attempted to repair a lens and ended up with anything other than a pile of useless parts. Either replace it or have it professionally repaired.

,

Anything is possible, but I doubt it's wise.

(Both from forums.popphoto.com)

And:

The safest way would be to send it to Canon Service Centre or a repair shop and ask for a quote on the repairs.

(From photo.stackexchange.com)

So at least you have to be attentive when you want to fix a lens yourself, there is a reason why repairing at 'pro centers' is often expensive.

But still there are enough people who fix the problems without doing even more damage to the lens and have a lot of fun/profit of it. Of course is not every lens problem the same, but when you face an issue it seems smart to me to look on the internet if it is an often occurring problem with a known treatment. When you have decided to do it on your own you have to work well structured; in a clean, well lit room and you have to know exactly every step you take, because you have to do all those steps 'in reverse' after the fix.

Tl;dr: A lens (and so is the focus mechanism) is often made out of a lot of relatively fragile, small parts which could break quite easily. When you want to fix it on your own you have to do research and you have to have a certain amount of knowledge and skill. There are never guarantees.

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This doesn't answer my question. I didn't ask about how to repair a lens, it was a question about what specific technical problems could cause the (manual) focus mechanism to jam and whether a third party repair shop is likely to be able to fix these problems. –  Chinmay Kanchi Apr 17 '13 at 22:48
    
Bending of an inside part. (seen at canon 50 1.4). Breaking of cables (in general). Breaking of parts due to physical forces(bumping, hitting, falling). There are a lot of possible causes, some can be repaired, some not (at least not for a good price). So it depends on the lens and the problem. –  FW. Apr 17 '13 at 22:51
    
I sort of knew the 50 f/1.4 would come up... That lens is a bit of an oddball, and notoriously fragile. That one shows up on eBay a lot. I wouldn't touch a broken one even if it was free. Canon's quotes tend to be particularly high for that lens as well, nearly as much as a good used one. –  Chinmay Kanchi Apr 17 '13 at 22:57

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