Back focusing camera rather than lens

EspressoJunkie

EspressoJunkie

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Greg
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I bought a Canon 60D off eBay and a Tamron 17-50 (separate sales) a few days ago. The seller had great feedback, and the camera itself was like new, so I genuinely don't think the seller was aware of the issue.

I found a lot of the shots ( but not all ) were out of focus, and given my history with Tamrons I assumed it was the lens. So in the interim I borrowed my friends Canon 50mm 1.4 over the weekend, and I was surprised to find that the issue was still there. It's mainly noticeable at f1.8-4, and its not all the time, but to me it would indicate that there is some sort of issue with the actual camera, which is something I've never come across before. Obviously shooting at 1.8, 2.8 etc makes it difficult to nail focus in certain situations, but this happens about 75% of the time, even with the camera and target stationary, and there have been quite a few occasion where the focus has locked on, but still given clear back focus. I have of course eliminated human error, and there's definitely something not right.

Being from eBay I know I'll be able to return it, but I just thought it was interesting as it was the first time I've come across it.
 
It's quite feasible, Greg. Most scenes that we shoot have closer detail lower in the shot and the farther points towards the top. In camera terms the (sensor capturing inverted) then the far focus is the bottom of the sensor. If the AF sub mirror doesn't return to the correct (45 degree) angle then it'll direct a point slightly further away to the AF sensor in use and you'll see what you're seeing.

Gravity might be playing a part (depends on the reason for the error) so I'd try a shot in portrait (an oblique shot of a flat surface), check whether it's near or far focused and then another portrait shot with the camera inverted (shutter button at the bottom) and see whether you get a near focused shot.

Hopefully that made some sense.

Bob
 
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You can't conclude it's the camera because two lenses back focus. It could be two lenses which back focus. On the other hand, with those two lenses, clearly the plane of the AF sensors could be adjusted in the camera to the average back focus of the two lenses which would improve the AF -- with those two lenses. You might then find it front focusing with the next two lenses you tried. DSLR-type phase difference AF using separate AF sensors has inherent problems of calibration & lens variation which is why the best DSLRs with the best AF systems also offer micro focus adjustment per lens.
 
It's neither the camera or the lens that back focus. It is both together. Does the 60D have AF micro adjustment? It may be worth sending your kit off to get calibrated.
 
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Thanks for the replies everyone.

Regardless of what may or may not be causing the issue it's definitely there, I've used enough cameras and lenses over the past few years (look at my classified stats!) to know when somethings amiss!

Obviously I could send it away for calibration etc but it's much simpler to return it and look for another one.

So if anyone's selling a 60D (or a cheap 70D) give me a shout! :D
 
Canon Bob said:
How can micro focus adjustment be used to correct an error that is only there "75% of the time"?
Click to expand...
Changing the focus success rate from one in four to three in four would be a worthwhile improvement.
 
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