topic Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)? in EF & RF Lenses

Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Tue, 17 Feb 2026 13:52:38 GMT

Hey yall, I picked up a used copy of a 100-400 ii a couple months back to 'upgrade' from my 400mm F5.6L prime. That lens was razor sharp and I loved it, but I wanted the zoom and the equal if not better sharpness from what I read online. At first I thought it was fine and that I was maybe just missing AF, but I had a hunch something was not right. On Saturday I photographed a bird swimming on a lake (clear background, bright direct light) and I noticed the pictures really were not sharp on zooming in. This is where I finally felt sure it was not just a skill issue. I tried going through AFMA on my 7d ii to figure out if it was back/front focusing, and while it did sometimes, that was not the whole issue. It seems on direct comparison to the prime, it is softer.

I will attach a direct comparison photo, it is of a calendar taken pretty much front on with 1/40s, F5.6, and ISO 1600. It is clear especially in areas like the bottom left that there is a lot of softness that almost resembles diffraction artifacts going on in the zoom. It is not motion blur, IS is off so it is not IS, the pictures were taken with a 10 second timer on a tripod so they are totally still. They were manually focused the exact same way, it is not AF. I have tried with and without lens hood, it is not caused by light on the front element.

The pictures are linked in this reddit post since I don't have them on this laptop and I can't upload .webp: https://www.reddit.com/r/canon/comments/1r6j2sf/comment/o5r9eei/

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

kvbarkley — Tue, 17 Feb 2026 14:02:01 GMT

Here are some simple tests you can try:

https://bobatkins.com/photography/technical/testing_lenses.html

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

shadowsports — Tue, 17 Feb 2026 14:11:35 GMT

Greetings,

I'm not denying the clarity. If you want to check front and back focus I would recommend incorporating a ruler or measuring device into your test environment. Better lighting would also be recommended. I understand front and back focus is not your real complaint since you say that portions of the frame are in sharp focus. As of this posting, the EF 100 400 mk II is still under support by Canon. If it needs service you'll be able to get it.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

kvbarkley — Tue, 17 Feb 2026 14:18:05 GMT

In the link I sent there is a focus accuracy test.

https://bobatkins.com/photography/technical/focus_testing.html

It uses a target like this:

which when put at a 45 degree angle will show the distance in cm.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Tue, 17 Feb 2026 14:22:52 GMT

Hey guys, thanks. I did do a ruler test to evaluate front/back focusing possibilities first and while I don't have those images on me at the moment, there didn't seem to be any hugely significant issue there. Yes it seemed to be backfocusing a bit, but even focused correctly the sharpness still did not seem right. I am 99.9% sure this is not a focusing issue.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ebiggs1 — Tue, 17 Feb 2026 15:24:48 GMT

"... my 400mm F5.6L prime. That lens was razor sharp and I loved it, but I wanted the zoom and the equal if not better sharpness ..."

The truth is the 100-400mm either version II is no where close to the IQ of the 400mm f5.6L prime. I can confidently say this because I made that mistake not just once but twice. Sometimes I am a slow learner.🤔 However, now I don't own the ef 100-4mm in either I or II version. I do have the ef 400mm f5.6L (once again!). Go back to the prime.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Tue, 17 Feb 2026 16:08:47 GMT

While that might be true, it really looks like it is severely underperforming other shots I see online from it.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Tue, 17 Feb 2026 16:20:59 GMT

I can also mention that while I didn't perform a direct test, my tamron 70-200 f2.8 g2 also certainly seems sharper as another point of comparison

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ebiggs1 — Wed, 18 Feb 2026 15:41:04 GMT

"... it really looks like it is severely underperforming other shots I see online from it."

You can't rely on anything you see or read on the ole inner web. I see that as a grain of salt, meaningless. Only believe half of what you read and nothing of what you see there. I know for myself what I saw and seen (twice).

"...my tamron 70-200 f2.8 g2 also certainly seems sharper ..."

Absolutely! That is an extraordinary lens as well as the 24-70mm f2.8 G2. Not an apples to apples comparison though.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Wed, 18 Feb 2026 18:46:25 GMT

well here’s another test shot, I will be sending it off I think but thanks

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ebiggs1 — Thu, 19 Feb 2026 15:06:02 GMT

"...I will be sending it off ..."

Probably best course even if for nothing more than peace of mind. Canon will check it out.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Tue, 24 Feb 2026 20:35:49 GMT

For anyone in the future with a similar issue: I was quoted $569 for the repair.

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ebiggs1 — Wed, 25 Feb 2026 16:06:09 GMT

What were they going to do for $569 bucks?

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ryanengphoto — Fri, 27 Feb 2026 17:18:32 GMT

This is their official answer:

Repair Complete Comment:

"Your product has been examined and it was found that the lens was out of position causing poor image quality. Adjustments were carried out to sharpen resolution and dust was cleaned from inside the lens assembly rear element. Product functions were confirmed. Thank you for choosing Canon!"

So sounds like it was decentered in one of the many elements to me. Not too clear lol, they quoted based on 'a tiered rate repair', i assume because they would have to open it up to figure out what exactly was wrong before doing the repair and it was to cover themselves in case it was worse? Not exactly sure, but it's on its way back, fingers crossed it's sharp now 🙂

Re: Is this lens decentered (EF 100-400mm f/4.5-5.6 L IS ii USM)?

ebiggs1 — Sat, 28 Feb 2026 15:49:25 GMT

Good luck, I'm pulling for ya.