Question About CA on a Lens, and Did I Make It Worse?

OK, strange subject title, but here's what it means and thus my question. This may be a bit windy in order to set up my "what do I do now" question... here goes: I've had the Canon 17-40mm for over a year, purchased with my 5D (November 2007). I've been pretty happy with the lens although it seemed a bit soft, especially on the left edge. I had planned on sending it to Canon in Irvine one day (before the warranty expired) to do whatever it is they do to dial-in a lens that's soft.

OK, fast-forward 10 months to September 2008. The 5D2 is announced, I immediately sell my 5D and stash the cash until the 5D2 is available. I also set-up the 17-40mm adjustment with Canon, and ship it to them first week of Oct 2008. Perfect timing, right? I have no camera, let 'em fix the lens now whle I'm waiting for the 5D2. So, the lens comes back 2 weeks later (mid Oct) with a note that Canon did find the lens out of adjustment and that they fixed it. I sure hope so!

January 2009: The 5D2 arrives, I try my 17-40mm for the first time, and the sharpness is NOTICABLY better. I took many shots to test it out, and Canon really did return to me a totally sharp 17-40mm. VERY exciting. HOWEVER, I also got something else with the sharpness: Chromatic Abberation on the edges that's almost comical. Some images almost look like I took a green highlighter and traced the branches against a light sky, same with building edges. On narrow objects I'll get bright green on one side and bright magenta on the other. In some images it's beyond what Photoshop CS4 can fix. Looking back on my original 5D shots before Canon did the fix, there was some CA but not horrendous like this.

OK, granted, I now have 21mp to peep at, but it is pretty noticable even when you reduce the View way down on the image.

So, here's the "what would you do in this situation" question: do I return the lens to Canon and see if they can rectify the CA, at the risk that I'll lose the sharpness they gave me, or do I just live with the CA (which isn't in every shot of course) and just tweak and dance around it?

Paul, I'd phone Canon tech and talk to a real person, tell them the problem and ask their advice. It could be they can fix the CA issue without sacrificing your new sharpness, but it's also possible there might be an issue with the 5D2 that's a contributing factor. You might end up sending in both so they can work on them as a unit.

Are you a CPS member?

One final question. Have you made any decent sized prints of the images in question, and is the CA noticeable in them?

Yeah, I did plan on calling them unless the replies on here were "NO! Don't send it back!!".

No, not a CPS member, but I do have that info stashed somewhere because they are opening up the program again this spring for new applicants if I'm remembering it correctly.

No, I haven't printed anything bigger than 8x10 right now, I'm just going off the screen.

Well, I think it's harder to talk to an actual tech now that they've revamped everything at Canon. Even as a CPS member I'm now talking to a "technical liaison" or some such person who is not a service tech himself.

Starting soon (this quarter 2009, if it hasn't started already), CPS is offering a new three-tiered membership, with the lowest tier free, the middle tier $100 annually and the upper tier $500 annually. Available services, of course, increase with each tier.

As for the lens problem itself, I'm not technically sophisticated enough to know if fixing the sharpness issue could cause more CA or not.

The other challenge is the fact that the lens was repaired on Oct 2008 and went out of warranty in Nov 2008, but because of having to wait for the 5D2 I didn't get to test the repair until last month. Wonder if they'd even revisit the repair for no charge...

Paul, is there any way you could test that lens on a 5D and compare it to an identical 5D2 shot ? I've heard of others complaining that CA was much more apparent with the higher resolution sensor.

I've heard of others complaining that CA was much more apparent with the higher resolution sensor.

You know, I was wondering about that. Unfortunately, I don't know anyone around here who has a 5D... amazing, huh? But I tell ya, if that's part of living with 20+MP, then that's fine, at least I got a sharp version of the lens! I'll call Canon in a little while and bounce this all off of them. It's still 8:25am there in Irvine, they need time to get in the office and wake up a bit.

WOW. I just called Canon, got Tech Support on the line (fella named Nick), explained the situation, and he fully agreed that a sharpness adjustment shouldn't introduce CA, so he set it up for me to send it back AND sent me a prepaid UPS label via email. The original repair/adjustment has a 6 month warranty so it's all no-charge for this. How nice! Canon Customer Service wins a thumbs up this week.

Good for Canon Customer Service.
Be sure to let us know about the results. I'm intrigued.

Sounds like you're good to go! I love a happy ending.

Me too, Steve! BTW, I found the press release from Canon about the CPS program.

Bill, I'll post the outcome (such as, did they really fix the lens???).

Bill P., not sure if you're checking this forum, but the lens is at Canon right now, I just got the acceptance email (that they will adjust it for free). I'll let you know what happens!

Bill, I got the lens back from Canon today, only a 7 day turnaround. I took it for a test ride and am happy to report that Canon did the job! The lens sharpness is still excellent, and the CA is very minimal now, more like it was drawn with a pencil, not a highlighting marker. An adjustment of +5 with the Lens Distortion filter totally clears it up. I finally have a 17-40mm that is sharp and dialed-in, very excited. It did take two round trips to Canon Service to get it right, but well worth it to now have a sharp version. Canon gets another thumbs-up this week!

Thanks for the update, Paul. Great news that they were able to repair it! Somewhat amazing that their original "repair" knocked the CA so far out of adjustment!