The posterior of my Canon EF-S 17-55mm f/2.8 IS
I’m kicking myself. Maybe I shouldn’t be, because the guy at the camera repair shop says it’s probably not my fault, but still…
Here’s the story. After returning from the Burning Man festival, I knew my cameras needed cleaning but I put it off for a long time. So one day recently I got them out and started cleaning—and I noticed a weird little spot on the rear lens element of my Canon EF-S 17-55mm f/2.8 IS.
I can’t tell if it’s a water spot (how would that even happen?) or perhaps something that’s been there forever and I never noticed. It’s faint, and my test shots don’t seem affected by it, but it bothers me. This is my main workhorse lens, and I want it to be perfect.
So (Mistake Number One) I decide to clean this rear element, which up to now in its life has remained untouched by anything other than air. With hindsight, since my test shots don’t show a problem, I should have left well enough alone.
My second mistake was digging out some ancient lens-cleaning solution from the depths of my camera-gear box, a little bottle of cheap-o stuff that probably came free with a camera purchase, and which has been sitting there moldering and evaporating in my closet for years. I know it’s been leaking, because the outside of the bottle is damp. And if it can leak, it can evaporate, and god knows what essential volatile compounds have left it to to become part of the air I breathe. What was I thinking in applying this stuff to the virgin backside of a $1,000 lens?
Anyway, after applying some of this solution and attempting to wipe it gently clean with a fresh PEC pad, I get a sinking feeling in the pit of my stomach, because now there is a big rainbow-colored smear on the lens instead of a tiny spot. So I gently rub it some more. And some more. But the smear just seems to move around, never to go away.
In desperation, I apply a bit more of the solution and start with a fresh pad and try to very carefully wipe the old smear away before the solution has time to dry. But the results are approximately the same. I just have a moving smear.
So, using a succession of clean PEC pads, I wipe it vigorously, get a new pad, wipe again, and so on. As I do this repeatedly, the smear seems to finally fade until it’s a very gentle haze on my previously-pristine lens. I eventually decide that’s as good as it’s going to get, and I put the lens back on the camera to take some test shots.
Horror! The lens will no longer focus! The autofocus mechanism just hunts, and hunts. Zoom-zip-zoom-zip, back and forth. Even on simple high-contast objects in bright light, it just can’t lock focus.
Damn! I’ve ruined my best lens!
Frustrated and cursing myself, I take the lens to my local repair shop. I explain what I’ve done, and offer the theory that I’ve left some cleaning-solution residue on the rear element that is screwing up the focus. But the tech says, no, that lens element looks fine to him, and that it would take a hell of a residue to cause this. He takes it in the back to test it.
The verdict: The focusing motor that moves that rear lens element has “gone out.” But surely, I say, it can’t be a coincidence that the lens worked perfectly before I cleaned it, and not at all after I cleaned it.
“Well,” the technician says, “I suppose maybe by putting pressure on that glass as you cleaned it, you pushed it over the edge. It must have been right on the brink of failure, and you just tipped it over the line. But if it was that close to going out, it was going to fail one day soon anyway. Really.”
He seems sincere in this belief, but I know damn well that I took a perfectly good working lens and turned it into a $220 repair job. That’s what it cost for them to order the new focus motor from Canon and replace it. And I lost the use of my best lens for two weeks.
The moral to the story? I see several:
1) Don’t put cheap old lens solution on a $1,000 lens. Go buy a new bottle, moron.
2) If you ever must clean the rear lens element, don’t use much pressure.
3) If it ain’t broke, don’t fix it!
May your life be free of similar mistakes.
Never, ever scrub — damage caused by rubbing is worse than any original debris. First, use a can of clean, compressed air. Then use reagent grade methanol, ethanol, or acetone, in order of preference (try Gallade Chemical, a chemical supply company in Escondido or San Marcos) and use the “drag-wipe” technique: Soak a tissue with the solvent, drop an edge of it onto the surface, then drag the tissue across the surface, like pulling a fresh sheet across a bed, at a speed such that the trailing solvent stays at most 2 mm wide. Clean around the edge first if you can (because that’s where most of the dirt is), then across the entire surface at once, perhaps multiple passes.
Jack,
Thanks for the info! What’s your opinion of pre-moistened wipes for this sort of cleaning? I have some Zeiss wipes supposedly good for “all optics” from eyeglasses to lenses that I often use to clean the front filter on the lens. They contain isopropyl alcohol. Thoughts on those?
I’m generally suspicious of pre-moistened wipes because they could be designed for anything from eyeglasses to computer screens. (When I worked at HP the lab stores had some two-step wipes that left streaks and some regular wipes that were fine.) But I would certainly trust the Zeiss brand. Isopropyl alcohol is safe, but it evaporates a little too slowly for the drag-wipe technique.
Some of the pre-moistened wipes I’ve seen have a lot of solvent, so you might want to wring out some of the excess if you’re working around lubricated mechanical parts. Your motor could have died because it seized or because the solvent shorted it out, I don’t know, but reducing the amount of solvent might have avoided either.
Getting back to the original dirt or whatever it was… It’s odd that it appeared in a desert environment, it’s odd that it resisted cleaning, and it may be significant that the surface trouble was, as I think I see it in your picture, symmetrical about the lens axis. Did the lens experience any environmental shock? It all makes me wonder if maybe, just possibly, the coating was stressed by the heat and dryness, or a quick change in them, and your old solvent had enough non-volatile stuff in it to fill in the stress-induced voids in the coating. If this is the case the surface defect might reappear. Hope not.
moral of the story… brung it to the playa, the playa eats it, smear or not… doomed to failure… happened to me lots of times now…
i too have that ‘itch’ to clean lenses. i have several mc rookor lens from the 60s that belonged to my father. i just refound them lately after i bought a dslr and want to use them again.
all have molds or dirt. one day i just DECIDED that i would clean them myself. i got a set of small screw drivers and just unscrew all the screws that i could see.
i was able to clean and put the lens back. thank God that they were all primes and not that difficult to reassemble. but i did lose a ball bearing under the aperture ring that makes the clip stops. did not even know that i lost it until i read somewhere that there was suppose to be a steel ball bearing under the aperture ring.
goog thing the lens are again usable even with a smooth aperture ring!