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Old Oct 29, 2010, 9:05 PM   #1
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Default Tamron 70-300 lens not focusing, DIY fix

I still can't get over it, but somehow I managed to fix a Tamron 70-300 LD-Di lens that quit focusing the other day. The focusing ring would only move an inch or two in the middle of it's range which made the lens useless. The lens cost me less than $200 and I figured a repair would likely cost that much or more, so I didn't think I had much to lose. I held my breath and went for it.

I put a few paper towels on my workspace to catch any dropped bits and a piece of white paper to put the parts on in the order they came off along with the screws that held them in. With a magnetic jeweler's screwdriver I took out the screws holding the lens contacts and then the ones holding the baffle tube and removed it. (That's the ribbed piece with the rear lens element at the bottom.)

Next I moved the ribbon cable and the lens contact board out of the way and removed the mount. Then I took out the brass focus drive shaft by tipping it slightly towards the center of the lens and pulling it out. I found a circular metal shim and 5 plastic ones underneath the mount and removed them.

There were two more parts that needed to come out next, one holds the diaphragm return spring and the other the diaphragm actuator. I removed them, carefully noting how they were assembled to the lens.

Once those were out, I took out the screws holding the circuit board and moved it to one side, exposing a small gear set underneath. I removed the screws and pulled the gear set out and right away noticed it would only turn part way because it was jammed by a tiny bit of black debris. I carefully removed the debris with a pair of tweezers, made sure the gears turned freely and then put everything back together, like they say, in reverse order of removal.

I didn't take any pics because the disassembly was pretty straight forward, and besides, I really didn't think it would work anyway. I'm surprised - REALLY surprised - that it did, and the whole thing took less than an hour. Focusing actually seems smoother and a little faster than before.

Would I try this with an expensive lens? I don't think so...
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Last edited by toshi43; Oct 29, 2010 at 11:31 PM. Reason: oops...spelling mistake
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Old Oct 30, 2010, 12:35 AM   #2
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I like the faster focussing part of the story. My lens should arrive at your location sometime tomorrow..LOL
I also own this lens, and for the money, it's hard to beat!
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Old Aug 22, 2011, 3:52 AM   #3
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OH MY GOD

i went through the process of siging up to this forum to thank you !!!
i had a little look inside with a nervous mind, but followed your instructions carefully and noted everything as i went, i have just fixed my lens, i might treat myself to some new accessories for it as i havent been able to use it for so long. i had exactly the same issue, a tiny bit of metal debris was blocking the gears from working properly

thanks again very much

BEN
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Old Aug 22, 2011, 8:25 AM   #4
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Good job! Congratulations. This is a tricky process if you haven't attempted it before. I highly recommend having a very large, clean surface, as sometimes, there are springs which tend to fly off and disappear. Also a good idea to take pictures as you disassemble, in case the lens has to sit a while before you are able to put it back together. Very easy to misremember how the parts go.

brian
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Old Aug 22, 2011, 10:35 AM   #5
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toshi43,

Congrats on fixing your lens.

Sometimes its hard to justify sending a lens out to be repaired. But rather than let it collect dust or end up in the dump, it may be worth the effort to try to see what's inside.

Take care, Glen
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Old Sep 8, 2011, 4:35 PM   #6
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You're welcome, glad I could contribute something useful. The lens is still working great, but I don't seem to be using it much since I got my HS20. Wonderful camera!
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