Tamron 17-50 focus problems

dt2indenton

I have the Tamron 17-50 on a Canon 20d now for about a year and I'm not terribly impressed. But maybe it's just me. I can't seem to get a good focus when shooting specifically people. On this past fourth I took some daylight pics in Av with the aperture set 7.1, shutter at 160, ISO 200 with Evaluative metering on. The pics are just average.

So, the question is, if you are taking pictures of people and you want all of that person(s) in focus, what settings should i use?

Thanks,
Darren

ziggy53

First, confirm focus accuracy for that lens/camera combination. Make sure you are in One-Shot mode for these tests. Please do all of the following:

1) A brick wall, shot straight on and squared with, using a tripod. This is a pretty good test for front-focus, back-focus, field curvature and vignetting issues. Make sure to test the lens with at least twice MFD, as well as your typical shooting distances. If the camera/lens does not pass this test, it's rather pointless to proceed any further.

2) A fence line or similar, shot at an angle to the subject. Put a singular strong-contrast target on the top of the middle post and use a single focus point in the camera to focus against the target. This shows focus accuracy and/or how easily distracting for/aft objects influence AF accuracy (compared to the above wall shot). It also shows bokeh tendencies at different aperture settings.

3) A focus target/chart like in the following:

http://regex.info/blog/photo-tech/focus-chart

I do recommend testing these charts at twice minimum focus distance or greater. Most lenses, especially most zoom lenses, do not do their best at MFD. True macro lenses are the major exception.

4) A US stop sign, or similar very high contrast signage, both centered and off center and to the side and/or corner. This can show chromatic errors and off-axis errors.

5) A spectral highlight at night. (Point source ideally, but a street light at some distance will do.) Try to avoid "blooming" of the source but allow some white clipping. This shows internal reflections and dispersion problems. Again, test both in the center and with the subject at the sides or corners.

6) Now just shoot "typical" subjects for your use of the lens(es). It's important that the lens perform correctly for your intended uses.

After you finish the tests, if you want some further opinion about the lens, feel free to post links to full-resolution images of the tests with full EXIF intact. Then we can talk about AF settings and such.