17-55mm front-focusing...how bad is it?

[alex]

John, thank you so much for taking the time to construct this informative response! I will attempt to redo my test using some combination of methods you mention above. You

[Richard Lane]

Hi Alex,


The fact that you

[scalesusa]

Alex, with your setup, the camera could indeed lock on to different lines at different times. That tape with all the closely spaced lines is just inviting this.


Here is a proper test chart designed to help you lock onto the intended line. It does make a difference. Notice that you can print different charts depending on your printer. I use the faintest chart and always lock on to the center. i tried some of the more dense charts, and AF did not always lock on to the center, so you might need to try different ones.


There is a excellent discussion of things that can go wrong while testing, and a nice section on how to intrepret the results.


I found it to be useful as a starting point, once you understand whats going on, then there are a number of good ways to check autofocus.


regex.info/.../focus-chart

[neuroanatomist]

Here is a proper test chart designed to help you lock onto the intended line.

The only issue I have with the chart you linked is that the focus target is still a horizontal line, which will predominantly activate the f/5.6 part of the AF point, and not the more precise f/2.8 sensor (which is the one I'd want to use, if the lens was f/2.8 or faster.

[alex]

Well everyone, I performed another test today on the coffee table, using John's (kindly) provided star-burst focus chart. Propped the tape measure up on some building blocks (had to sneak into the napping boys' room to get them!), tried to align everything to the best of my ability, and did some shooting.


This time I took about the same number of shots as previously.


Boy, were these results DIFFERENT from before. unbelievable. John, you must have been right about the requirements for my camera's AF system. The amount of variability between the shots was minimal. Not only that, but to my eyes, my focus problems are negligible. Of course, that's assuming that I lined up the paper focus chart in the same plane as my camera's sensor and also lined it up with the tape measure correctly. Again, I did this to the best of my ability.


I attempted to set the plane of focus so that the line right below the 7 would be in focus.


Settings were the same as before, 55mm, f/2.8, ISO800, either 1/40 or 1/50 depending on the shot.


First shot is the MF, LiveView. I focused on the paper in the LiveView screen, not the number on the tape measure.


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Number 2, AF (the center point focus is aimed at the paper just above and to the right of the center star burst, directly horizontal and to the left of the 7)


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nearly identical (to my eyes), and all the AF shots I did were like this.


Finally, a nearly 100% crop of the AF shot above.


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What do you guys think?


Thanks!


alex

[Trowski]

Very much looks like your lens is performing extremely well. I think the problems you were experiencing before were due to the problems John pointed out with your testing technique. I'm tempted to assemble that chart John linked to, pasting the starburst pattern onto the focusing area, and then test out some of my lenses. That being said, I've never really noticed any problems with my lenses.


John, I really think you should write full articles for a photography website (or perhaps start your own). So often I find your posts to be the most helpful, well-written, and logical responses to the many questions posed on this forum.

[Richard Lane]

John, does it again! I think your images look very good now, so if you are shooting targets you should be in good shape.[]


Now, see if you could use this information when focusing on real subjects and see if you're happy with the results, because the target is easier for the AF system to lock on to, so for real subjects make sure that you choose a focusing location with sufficient contrast and/or delineation, like the corner of someone's eye, or their chin which is approximately in the same plane as the eye.


Maybe, you could post some real world shots. Ones that you weren't happy and some new ones. If you could post the shots with the red focusing square visibly on them, that would be helpful.


Rich