I seem to have a focus issue with my new Tokina 11-20. It's mounted on a Canon 1000D(XS)enter image description here

The camera is on a tripod.

The lens is wide open F/2.8, at 11 mm. I manually focused on the T on the box using liveview for the "manual" shot.

Then I manually focused the lens to infinity and let the camera refocus using the center cross point, centered on the T. I also did a shot manually focusing to shortest distance and let the AF focus again; the result was identical to the previous one(still off).

I called the shop, they're willing to give me my money back, but they're out of stock. Basically I can't get a replacement any time soon (no competitors either).

So I guess my question boils down to this; Is this enough to be classified as a defect? Or is another lens just as likely to show the same inaccuracy(do I just deal with it?)?

The focus also seems to be very persistent, it "nails" it everytime, only 3 cm behind the subject. Is it possible to calibrate it?

Note: no focus microadjust in the Canon 1000D

  • 1
    Unless the target is perpendicular to the sensor in the camera, which doesn't appear to be the case here, the results of your AF test will not be accurate.
    – Michael C
    Jul 15 '16 at 2:47
  • So I shouldn't expect the AF to be accurate in a real world scenario(where targets are rarely perpendicular)? Thanks Jul 15 '16 at 9:58
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    You should expect it to do what you have told it to do, but you shouldn't expect it to do what you think you've told it to do when you haven't learned its language.
    – Michael C
    Jul 15 '16 at 10:00
  • Quite honestly, the first image looks soft due more to camera movement/vibration than anything else. Nothing is as sharp as the sharpest parts of the second image. If your shutter speed was in the 1/2 to 1/100 second range it is possible mirror vibrations could have caused the softness.
    – Michael C
    Jul 15 '16 at 10:08

It is within the realm of possibility that the lens is back focusing. To confirm this and measure exactly to what degree, though, the target and distance scales need to be properly aligned with the camera.

There are a couple of reasons why good alignment is needed to get a valid AF test measurement:

  • If the camera is aimed at an angle to a target such as you have created then the distance from the camera to the "T" on the target is not precisely the same as the distance to the "0" point on the scale beneath it and to the side.
  • Your AF system will attempt to focus on the area of greatest contrast within the entire active area of the AF point(s) selected. The area of sensitivity for most AF points is quite a bit larger than the indicator square that you see in the viewfinder. Modern AF systems often have overlapping areas of sensitivity between adjacent points. If the camera is not perpendicular to the target then the camera may be trying to focus on an area closer or further from the camera than the spot at which you think you are aiming it. For more, please see Which offers better results: FoCal or LensAlign Pro? and Are of cross-type focus points more accurate, or just faster?

If it turns out the lens is consistently missing in one direction with the 1000D, which lacks AF Micro Adjustment capability, you have a couple of options:

  • Exchange the lens and hope the manufacturing tolerances of the next one matches up better with the manufacturing tolerances of your camera.
  • Send both the lens and your camera to an authorized Tokina service center and let them adjust the lens to the camera.

With this lens mounted on a D5500 I have found that AF accuracy is a problem using the viewfinder ie. focusing using the AF sensor. In this case it front focuses and the severity of the eror is less at the 11mm end of the zoom range and is worst at the 29mm end. Almost the same results were found using a Nikon D3300 camera.

If the lens is manually focused using the in focus indicator in the viewfinder the result is the same and the amount of slop in the indicator from lit to unlit whilst rotating the focus ring is huge. If the lens is focused using live view the result is accurate and this is easy achieve with the touch screen on the D5500 being suitable to "pull focus". The focus results that I obtained were similar before and after the lens was returned to the Tokina agent for calibration without the camera. ie. when set up to factory specs it was still front focusing but not on "live view" which uses the main sensor to achieve focus.

Conclusion: This is a design issue for Tokina to address as it will not operate properly in viewfinder focus mode on two current models of Nikon DX cameras.

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