Canon 55-250 Focus Accuracy

The Canon 55-250 lens does not have a USM focus system, so the front of the barrel rotates & extends, plus it's not super fast. However, at least on my Canon 40D, it's darn accurate, especially as you zoom in. To test this, I used Moire' Interference Patterns at various focal lengths and here are full-size center crops using the auto-focus, and then doing "best" possible with Live View. The 40D was tripod mounted about eight feet away for the 250 and 200 shots - about six feet away for the 55 and 90 pictures. Timed shooting was used to minimize any camera shake and aperture was maximum possible with ISO 800 - shutter speeds were 1/60 to 1/160.

Note the fuzziness at full wide at 55mm - this was repeatable and is slightly back-focused, although it may be due to the fact that the test image isn't large for super-precise focus since if I moved to the minimum focusing distance, it was then dead on. I'll do some real-world testing when I have a chance, especially since this just tests close-in focusing.

Auto Focus at 250		Live View at 250
Auto Focus at 200		Live View at 200
Auto Focus at 90		Live View at 90
Auto Focus at 55 - slight back-focus		Live View at 55
Auto Focus at 55 at 3.6 feet		Auto Focus at 55 at 3.6 feet