Check your lenses

....occasionally....I am not saying right now. ;)

I have been intending to write this post for a while. Last November/December, I was comparing my newly arrived Sigma 150-600S to my 100-400 Mk I lens. I posted several shots, and among the observations I made was that I was getting much more consistent focus results with the 150-600S. A couple of you wondered if there was something wrong with my 100-400 I. I assured you that I've used it for years with good consistent results. :rolleyes: In fact, the lens had just been used a month or two previously.

Then I was comparing test chart shots of the two lenses and I noticed that the left side of the printed ISO 12233 chart were much sharper than the right with the 100-400 I (the Sigma checked out fine). So, I thought, I had a decentered element with the 100-400 I. This is similar to the results where I thought I had a decentered element with my EFS 15-85, which has sat unresolved ever since I bought my 5DIII.

As I am finally selling off most of my original kit (7D, EFS 15-85, 580 EX II are now in better hands) as motivation, I sent both the 15-85 and 100-400 Mk I in for repairs to Canon.

Both came back fixed with similar description in the service details:

15-85: "Your product has been examined and it was found that the internal component had been impacted causing the focus to operate improperly. The internal component was replaced. Product functions were confirmed." Under "Part Description" "Barrel Ass'y, Fixed. Gyro."

100-400 Mk I: "Your product has been examined and it was found that part did not operate properly causing the focus to operate improperly. The part was replaced. Product functions were confirmed. **If same problem occur.pls send us with the body" No description of which part was repaired.

So, even though I do my best to take care of my gear, things happen. Both of these issues manifested themselves as inconsistent focus across a flat plane (ISO 12233 chart with the 100-400 and a landscape scene with the 15-85---later confirmed on the ISO 12233 chart).

The moral of this post: it does not hurt to occasionally check your lenses to make sure all is well. In the future, I think I'll probably do that with all my lenses once a year or so.

BTW...the buyer of the 15-85 was fully aware that I had found and repaired an issue.

Thanks...Brant

Thanks for the heads up! Excellent advice.

I think part of your suggestion is: Establish a baseline early on. Kind of like a cardiologist or X-Rays!
Once I know my lens is performing as it should, I save my Reikan FoCal charts for my micro adjusting, aperture and AF performance. Also like you, ISO chart shots so I can judge performance at a glance if I suspect something is amiss.

Regardless of the care you take, things wear out even without use. Especially with the use of so many plastic parts now, and so many crazy things in the environment. How many of us have witnessed plastics yellowing or their compositions changing even in a darkened closet? I would think with the insanely high tolerances necessary in modern optics, the slightest degradation of any element inside a lens could cause a significant change in IQ.

But without establishing those charts early on, you could very well wind up second guessing yourself and maybe never do anything about it. As we see, it's a pretty painless process and I'm glad Canon promptly solved the issue.