Help! Focus jammed

Started Dec 30, 2009 | Discussions
wenhuashi New Member • Posts: 6
Help! Focus jammed

Hi, I got a 50mm f2 SMC Pentax A lens, its focus is jammed, but aperture works. Does anyone know what's wrong with the lens? How to repair? Thanks a lot.

GPGeneralPhoto
GPGeneralPhoto Senior Member • Posts: 2,156
Re: Help! Focus jammed

I have repaired some lenses. There isn't much point in repairing THIS lens. The tools you will need to do it PROPERLY will cost more than another 50mm f2 from ebay. A good JIS screwdriver set is around $20 shipped. If you need a spanner for the rings, that's another $20 or more. I bought a Pentax A 50mm f2.0 on ebay for a little less than $20 shipped. Sell it as a jammed lens on ebay and buy a different one.

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OP wenhuashi New Member • Posts: 6
Re: Help! Focus jammed

Thanks for reply. It seems very troublesome and costly.

Any other opinion from other friends? thanks a lot.

Just1moreDave Regular Member • Posts: 421
Re: Help! Focus jammed

wenhuashi wrote:

Hi, I got a 50mm f2 SMC Pentax A lens, its focus is jammed, but aperture works. Does anyone know what's wrong with the lens? How to repair? Thanks a lot.

The lens was probably dropped. This problem is pretty common with the M50/2 and A50/2. I don't know whether it's a design flaw or just many more lenses produced.

The fix is not that hard. It'll take longer for me to type this than do it. There's a plastic beveled trim ring around the front element. It's supposed to unscrew through the filter threads, but dropped lenses often have damaged or not-round threads. It's not that hard to pry the trim ring out in this case. There are even two slots at its edges for a thin tool.

The trim ring hides three screws for the filter ring. I have a Phillips #00 that fits these screws well enough, and they aren't that tight. Remove them and the filter ring comes off. This is a good time to try and repair dents if you want.

Now there are three more screws which attach the focus ring to an aluminum track. More obvious screws hold down a brass washer that keeps the front lens group from falling out; don't bother with those. The screws you want are deeper, just inside the lettering SMC PENTAX-A 1:2 50mm. With luck they won't be hidden behind the ears for the lens mount. I was able to get my screwdriver in there anyway. Remove these screws and the focus ring comes off.

Now you see the aluminum ring. Careful inspection will reveal that it is not parallel with the plane of the lens mount. Look at the gap between its lower edge and the ring with the DOF scale. One side probably has no gap. You can use a knife blade or flat screwdriver to pop this aluminum ring back into place. Some care is required to avoid damaging the ring or DOF scale, but it shouldn't require much force. When it pops back, the aluminum ring should turn smoothly and the lens should focus again.

Move the aluminum ring so that the lens elements are as far back as they go, back towards the mount. Put the focus ring back on with the infinity symbol lined up with the orange diamond mark, and only one screw tight. Mount the lens on your camera and focus on a distant object, something that should be a few miles away. The distance scale probably reads 10 meters or so. The lens can focus "beyond infinity" now; you need to set infinity correctly or the space-time continuum will be damaged. Loosen the tight screw and move the focus ring without changing focus, until the infinity symbol again lines up with the diamond. When you're happy with that setting, tighten all the screws and continue reassembly.

OP wenhuashi New Member • Posts: 6
Re: Help! Focus jammed

Hi, Dave,

thank you so much to write such a detailed instruction. I'll try with it, and it's a good opportunity to learn how to repair lens, should be very interesting. I really appreciate your great help. I'll let you know no matter it is successful or not. thanks again.

Wish you a peaceful and prosperous New Year!

wenhua

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