reddtekk Offline Upload & Sell: Off
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Hello folks, I finally found a price that I could swallow for the 17-55 2.8 IS USM Canon lens. I got it with a hood, a pretty good gouge in the front element and a bunch of dust in it for $300 on eBay. Although the dust and gouge don't cause any significant issues with IQ that I can notice (granted, this is my only experience with the lens...), I still plan on repairing it (since I can't leave well enough alone and I suspect it may be taking away from contrast a little bit and/or cause flaring) so I felt that it would be good to start a forum thread on this subject. These get a lot of use and get banged up and full of dust, so maybe someone else can benefit from my experiences.
Repair items:
1. Zoom binding - can't zoom when the lens is facing even slightly upwards.
2. Scratch in front element
3. Significant amount of dust visible inside the lens
I'll start with #1 because I already fixed it!
FOLLOW THESE RECOMMENDATIONS ENTIRELY AT YOUR OWN RISK!!!!!!! I am not the best of the best, but I posses a fairly high level of mechanical aptitude. Lens repair is not for everyone. Go into this understanding that you could irreversibly damage your lens!
This worked for me with the mode of failure that I observed in my lens - that doesn't mean that it will fix yours!!
I removed the rubber sleeve on the zoom barrel. There are several slots and screw heads revealed and an electrical contact.
In hindsight, I should have first marked the position of the electrical contact (scribe, not a magic marker job - it appears to me that the contact points are fairly high resolution). That should be removed before further disassembling the zoom assembly - I didn't and I bent the pins. I got lucky and didn't break any when I bent them back. Note that it is slotted so it will need to be set back to precisely where it was.
Next I removed the three screws holding the brass guides in the circumferential slot towards the rear of the area covered by the rubber zoom ring grip. Once this is done the zoom ring will flop around freely. There is a tab that it engages with and when you reassemble the lens you'll need to line them up.
Fiddle with the zoom position until you can see the screw heads for the guides in the axial slots. On my lens, two of these were loose.
I tightened them (not lug nut tight - these are small and only threaded into plastic or aluminum!), reassembled the lens and it made all the difference in the world. I plan on disassembling this again in the future and putting a couple drops of penetrating Loctite on the screw heads to keep them in place. This is not my idea - Canon had put this on the screw heads before but it worked loose.
I could see the possibility that this could cause serious damage to the barrel of the lens - if the screws flop around in those holes enough, they will get wallowed out and then they won't be able to be tightened. If you notice excessive play in the front of the barrel and it gets hard to move the zoom, fix it or get it fixed before you have to buy parts...or worse a new lens!!!
On the subject of parts - I called up Canon Parts today for the front element - friendly people and (I think) that $146.90 is reasonable for a front lens element on an $850 lens. I can't buy it right NOW, but I'll do so in the future and I will continue this thread with how I go about replacing the front element and removing the dust.
The dust removal is well documented but the front element replacement will involve calibration as it is mounted on a helical cam of some sort (I haven't yet gotten a good look at it, but most comment about it). I am open to suggestions on calibration but I'm considering setting up a couple of focus test subjects (diagonal ruler or something of that nature) at various distances to test the lens and get it set up. If anyone knows a little more in-depth what the proper mechanical calibration procedure is for this lens, I'd be very happy if they wouldn't mind sharing some knowledge.
Thanks very much for reading!
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