New EF-S 55-250mm lens defective??

ScubaDude · Sep 12, 2011

I thought I knew the answer to this, but now I'm not sure, so I thought I'd check with the experts since this is my first autofocus camera and I hate to jump to conclusions.

I got my Canon EF-S 55-250mm f/4-5.6 IS II last week, and noticed that it often had difficulty focusing on single objects that had no close background objects (see attached image for example). Today I gave it a thorough test, and I think I have a lemon. In taking the attached photos, it worked fine zoomed all the way out to 55mm. Zoom in even a tiny bit and it would hunt for 5-10 seconds and then give up. If I set it to "AF Point Manual Selection" it worked fine... if I put the target on whichever point I picked to focus on (I tried several manual points besides the center one) it would snap right into focus. Switched it back to "AF Point Automatic Selection" and the problem came right back. I experimented with various shooting modes, ISOs, apertures, etc. and got the same results every time. My 18-55mm kit lens works perfectly*, so I don't think the fault lies with the camera (*altho, if I point it up at the sky with just the tip of the tower on the bottom-most focusing point, it does exhibit that behavior).

Is this normal or do I need to send it back? I asked on a different forum, and the only answer I've received (from a long-time member with a more upscale Canon and L-class lenses, so I assume he knows what he's talking about) is that this is normal and in that situation I should pick the focus point manually. Is that correct? I've been able to get around the "problem" by aiming the camera at an area with a wider variety of things to focus on, then aim at my target once the focus is locked in.

Thanx in advance for your input.

test by turbodog2000, on Flickr

Tomasko · Sep 12, 2011

Best habit is to set the AF point manually either way.... Camera nor your lens know what are you trying to shoot and it gets easily confused.

Big Mike · Sep 12, 2011

There are certain (vaguely predictable) situation that might cause the 'auto point selection' to fail. I'd guess that it usually occurs in low light situations...but the facts is that AF works by detecting contrast...so if you scene is lacking contrast (like a clear sky that you mentioned), then your AF is much more likely to struggle or fail.

Auto point selection can be a bit of a mystery at times anyway. Sometimes it will pick the same thing in a scene, sometimes it will choose something different each time, some times it will cycle through several different things...possibly moving from closer to farther away.

But the point is that it's the camera that is choosing what to focus on...not the photographer. That is why I teach my students to use a manually selected point and purposely focus on their subject. But of course, there are times when auto point selection might be beneficial, but it's up to you to find those situations.