Back focussed


Today I went to pick up my 70-300 mm L lens from the Canon service center at Vivocity. They had called me more or less 2 weeks ago to tell me the cost of the repair, and while this was a painful number, I said yes, of course. They also said that the repair would be done in 5 days or so, which was a bit off the mark. But fine: the final price was at least a little lower than what they had told me. Still a lot of money…

I was excited when I went to the service center. I have written often about this lens here on the blog and I think it’s clear that it’s one of my favorite gadgets. The focus speed and the insane output of perfectly focused, tack sharp images just made me smile every time I used it.

When I finally had it back, I mounted it on my camera body and tried it out.
Hm. The USM motor sounded differently: louder and arguably not as pleasing as before. Sure enough, they had had to replace it. Okay – maybe the newer USM motors simply sound like that. I took a few shots and I sort of had a weird feeling. I did not seem to be able to get the photos I wanted. I played around for easily half an hour in the shop but I could not put my finger on it. In the end I decided that I just might be seeing ghosts: it’s not unusual that I am extremely critical when looking at the photos on the camera display but am in the end very pleased when I see them on a computer screen.

This still bugged me.
So back home I continued to take random shots until I finally figured out what the problem was. It hit me when I took a photo of one of our fans. I had focused on the mesh of the blade housing and when highlighting the focus point I had picked for this photo, I could see that the part of the mesh on which the AF point sat was in fact not focused. But the part of the mesh just behind it was.

So there I had it: whatever they had done at Canon, it had resulted in the lens back focusing.

Naturally I was mad. At Canon.
But more at myself, because it’s always a bad idea to mess around with a lens. And the reason why it had to go into service was my own stupidity.

Now, in fact, modern cameras can be adjusted to a lens that is back or front focusing (thinking about it, this might be also the issue with Alex’ 400 mm lens – just in case you read this, buddy). It’s easy to find tutorials on how to micro adjust a Canon lens and this entry here suggests a particularly clever one at the bottom. So yes, this is not the end of the world and I can likely fix it even myself.

It still pisses me off.

Edit December 2:
I’ve been in touch with Canon. They’ve agreed to fix the problem for free, but requested to receive both the lens and my camera, which obviously means they will micro adjust the camera to the lens and not fix anything they have done to the lens body (which is likely a smart choice).
This will take two days, so I will have to do this once we are back from Europe…

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