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02-22-2016, 02:43 AM - 1 Like   #1
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Sigma 17-50mm F2.8 Ex Dc Disassembly DIY Repair ?

Hello Ladies and Gents,

I just purchased a broken Sigma 17-50 2.8. It has no zoom as the ring simply rotates and nothing happens. It's also upside down from where it should be.
The AF does appear to work though.
Aside from that there's a concerning amount of dust inside the front lens. Silly seller sent a very dirty lens. It had some crap on the outside too. Anyway he said the lens simply broke and he did nothing as far as repair. He just bought a new one.

I've had one other lens repaired before but it was seriously messed up.
This problem is nothing like that and I appear to have the tools to open this bad boy up.
I found one video that appears to be helpful here:

While my problem is different I could use some tips about whether I should try this or not.

Anywho I paid 60 Euros. Maybe it's a truly lost cause. I guess I'm going to find out soon. If you can find these lenses on the used market they easily go for 250+ Euros.

Many thanks for any help and tips!
You're all wunderbar!!
John

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Last edited by Iksobarg; 02-22-2016 at 03:00 AM.
02-22-2016, 04:37 AM   #2
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The first thing to do is pull the rubber grip off the ring and see if any of the guide screws/pegs visible underneath have fallen out or come loose. Based on how loose it is. it looks like someone might have done this already.
02-22-2016, 04:46 AM   #3
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QuoteOriginally posted by dcshooter Quote
The first thing to do is pull the rubber grip off the ring and see if any of the guide screws/pegs visible underneath have fallen out or come loose. Based on how loose it is. it looks like someone might have done this already.
Hi Boss,
There's no loose screws however there are loose taped on brass/copper plates.
Something small sounds loose and floating inside.
Awaiting your orders o/
Many thanks!
John
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02-22-2016, 05:08 AM - 1 Like   #4
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Those copper plates are merely dust covers. If you can spin the ring around and look through the little windows under the plates, you might be able to get the loose piece out (possibly a screw/screws with a delrin busing to make it a peg) and see if there is a visible screw hole where you can put it back in so it pushes the internal zoom as the outer zoom turns. It might be a deeper slot that you can see at some point as you spin the outer ring around. Also, there appear to be conductive zoom information strips on the inner barrel under the copper plates. When you take off one of them, there might be a small fork-shaped relay underneath that makes contact with the strips. If you remove this be very careful, since they tend to be quite easy to damage.

If you don't have enough access to fix your problem via the little windows, then you will probably have to remove the mount and rear section from the lens and the screws you see on the grip in order to slide the whole zoom ring off. Depending on the design, it might get quite complicated and fiddly, so be careful .

EDIT: while looking for info on taking off the rear, I just found this thread, which might help you:
DIY fix stuck zoom of Sigma 17-50 F2.8 EX: Third Party Lens Talk Forum: Digital Photography Review

It will also show you where the three screws are holding the front barrel so you can clean the dust out should you decide to do so. Depending on the barrel design, the element might be accessible from the front as well.

---------- Post added 02-22-16 at 05:20 AM ----------

Just saw this in the comments on the DPR thread:

"Well I managed to clean the oil off the back of my front element, the front label just peels off and 6 screws underneath hold the front element in place. Note the order you take the screws out, they are not all the same size."

02-22-2016, 05:35 AM   #5
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I'm sure you can disassemble it but can you reassemble it? Are you feeling lucky today, well do ya punk?
02-22-2016, 07:52 AM   #6
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QuoteOriginally posted by southlander Quote
I'm sure you can disassemble it but can you reassemble it? Are you feeling lucky today, well do ya punk?
Hi Again,
I sorta hit a wall here...
This lens does not match the one at dpreview or the youtube vid... between the two I have made some decent progress but....
there's two screws underneath the dustcovers. I've removed one but am concerned about removing the other as it looks to me like that little silver colored flange or whatever is just going to fall...
The zoom ring won't come off without the electric board there and I've unscrewed many but it's not yet loose.
Also I managed to right the zoom back to it's proper position.
and the little brass pin next to the lens is what fell out from the inside.
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02-22-2016, 08:25 AM   #7
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That's the contact fork I had mentioned, and it unfortunately looks like it's already been damaged. Underneath the fork, you can see a flange with a cylindrical projection. That is the lever to turn the zoom ring.

What you need to do is first remove the two screws on the fork. The fork will then be removable. Take it out, then rotate the zoom ring until you see a circular hole or slot that matches up with the lever. The brass cylinder will then drop into that hole, and there should be a screw that goes through the cylinder and into the lever, allowing the external focus ring to push the lever back and forth. If it fell out or is missing, you might have to scrounge up something else that will fit. Note that if this was caused by the user trying to force the ring when it was jammed, then there might be more disassembly required to unjam it as shown in the DPR artile.

Next, you will need to carefully straighten the tines on the contact fork with some tweezers that have been folded back under. When the zoom ring is positioned and locked down, you will see the contact strips under the proper window, and when you reattach the straightened tines, the tips should glide over the contact strips underneath. They likely were bent under when the detached ring was rotated too far and they got caught up on the zoom lever.
02-22-2016, 11:57 AM - 1 Like   #8
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Very useful post. Thanks Iksobarg, and dcshooter.

02-22-2016, 12:36 PM   #9
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QuoteOriginally posted by dcshooter Quote
That's the contact fork I had mentioned, and it unfortunately looks like it's already been damaged. Underneath the fork, you can see a flange with a cylindrical projection. That is the lever to turn the zoom ring.

What you need to do is first remove the two screws on the fork. The fork will then be removable. Take it out, then rotate the zoom ring until you see a circular hole or slot that matches up with the lever. The brass cylinder will then drop into that hole, and there should be a screw that goes through the cylinder and into the lever, allowing the external focus ring to push the lever back and forth. If it fell out or is missing, you might have to scrounge up something else that will fit. Note that if this was caused by the user trying to force the ring when it was jammed, then there might be more disassembly required to unjam it as shown in the DPR artile.

Next, you will need to carefully straighten the tines on the contact fork with some tweezers that have been folded back under. When the zoom ring is positioned and locked down, you will see the contact strips under the proper window, and when you reattach the straightened tines, the tips should glide over the contact strips underneath. They likely were bent under when the detached ring was rotated too far and they got caught up on the zoom lever.
DC, you're so awesome for this. Thank you!
I've unfortunately hit a wall as I do not have the right screw to fasten the cylindrical projection in place. I shook the lens to see if it's still in there and maybe it is but then I'll just need to keep tearing this little guy. Seems to me it should be in there somewhere.
On the other hand I'm also looking for this screw. Is that a run to the local Optometrist/eyeglass, electronic repair shop or a contact with Sigma? I did attempt cannibalize another screw from the available screws from the lens but nothing would work.
That's probably not a good idea, I know/

Anywho, here's a pic of where I think I am stuck. Does that look right because it doesn't look right to me. I'll try and reference an exploded view of this lens. I said "exploded," heheh.
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02-22-2016, 12:45 PM - 1 Like   #10
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That's looking like it is probably correct. The missing screw is probably metric micro screw of some kind. If you can find a variety pack somewhere, you might be able to find one that fits. Or head down to the local thrift store and buy some old lenses/cameras and tear them apart until you find something in there that makes a suitable substitute. I'm not sure if Sigma still sells parts to end users, but if you have the exploded parts diagram, you might be able to give them the reference number and order one.
02-22-2016, 01:11 PM   #11
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QuoteOriginally posted by dcshooter Quote
That's looking like it is probably correct. The missing screw is probably metric micro screw of some kind. If you can find a variety pack somewhere, you might be able to find one that fits. Or head down to the local thrift store and buy some old lenses/cameras and tear them apart until you find something in there that makes a suitable substitute. I'm not sure if Sigma still sells parts to end users, but if you have the exploded parts diagram, you might be able to give them the reference number and order one.
I'm on it boss!

Since I started working on this think there's a nice 2 or 3cm hair follicle sittin on the rear lens looking at me wanting out...
I might as well tear this bad boy down. I'm certain I'm going to regret it to some degree.
I did take a lot pics of each step of the teardown with the screws next to that stage but I think that's not going to help a lot.

I need a good fitting meme about now...
someone bloody hit me.

"I'll be back"
02-22-2016, 02:23 PM   #12
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A good source for minuscule screws can be those on the hinges of glasses. Another source for tiny screws could be an old watch repair shop, though a rarity nowdays.
You could even maybe fit there a screw from another part of the lens, one that maybe is not that critical/important
02-22-2016, 02:38 PM   #13
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I have a lot of this mini screws, from a lot of lenses transformed in astro tools. I think that I will sell some, together with some parts, from different lenses, I use no more.
02-27-2016, 09:16 AM   #14
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Progress!
I located the culprit screw which had ironically fallen out and jammed the very mechanism it was a part of.

However earlier in the day (and more ironically before I encountered the original screw and apparent cause of the problem) I visited a watchmaker in town (to locate a replacement screw ) and in about the fifteen minutes that the lens was there he managed to lose another screw into the abyss.

As far as I know it might be the reason the zoom does not fully travel now. I shake the lens and hear nothing so this unfortunately probably means I have to further disassemble.

So my take away is that I should have just located the first lose screw. Arrrgh!!

Anywho, here I am:
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02-27-2016, 09:41 AM   #15
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I found nothing clearly obstructing the zoom mechanism, a screw or what not. I looked closely in the recesses. I'm thinking the interacting surfaces of the zoom mechanism need to be disassembled.

I also concurrently wondering if maybe I could get away with sending only this part in for repair... dunno...

I'm concerned about going any further.

Anyway, this is sort of fun. I've never take a lens apart.
Boy, is this going to be fun to put back together!??!? (if I ever get that far!)
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Last edited by Iksobarg; 02-27-2016 at 09:58 AM.
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