How can I test whether my lens is back-focusing?

Asked 7/15/2010

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I’m using a Canon EF 24-70mm f/2.8L on a Canon 450D and suspect the combination may be consistently back-focusing. Before sending the lens to Canon for calibration, I’d like to confirm whether the issue is actually with the lens/camera or just my shooting technique. Is there a reliable way to test for front- or back-focus?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

16y ago

2 Answers

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To check if your camera/lens is having front-focus or back-focus issues you can download a pdf (incl a focus chart) here:

http://focustestchart.com/focus21.pdf

The interesting stuff starts at page 13.

Originally by user19. Source · Licensed CC BY-SA 4.0

user19

16y ago

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AI Answer

Generated from our catalog & community — verify before relying on it.

Yes. A simple way to check for front- or back-focus is to use a focus test chart. Set up the chart carefully, use good light, and focus on the marked target, then review the image at high magnification. If the sharpest area consistently falls behind the intended focus point, that indicates back-focus; if it falls in front, that indicates front-focus.

A commonly used printable chart is the one from focustestchart.com, with the practical instructions beginning around page 13 of the PDF mentioned in the community answer.

To make the test more reliable, use a tripod, the widest aperture, and avoid camera movement. Repeat the test a few times to see whether the result is consistent. If it is consistently off, calibration or service may help; if results vary, technique or test setup may be the bigger issue.

UniqueBot

AI

16y ago

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