Superzoom unable to autofocus at infinity at mid-zoom focal lengths

Question

I have an inexpensive "superzoom" camera that functions properly and fills my needs but has one problem I seem unable to resolve. It is a GE Power PRO X500 camera with which I have taken several thousand photos, most of which I am happy with. The problem existed on 3 identical cameras which I tried from the same retailer, so it is not a single unit that is defective. For this reason I have not involved the manufacturer's help desk. From what I've read online their usual solution is to send out a refurbished unit in exchange, and customers are unhappy with this arrangement. The issue is that it has extreme difficulty focussing at infinity (subjects more than 50 yards/meters distant in broad daylight) when the zoom is at it's midrange (between about 24-30mm on the 4.9 to 73.5mm lens). Focus at midzoom works just fine when the subject is nearby (less than about 50 yards/meters). When it has difficulty, either the center focus rectangle remains red whereever I point it (at distant trees, houses, vehicles, etc) with a completely out of focus result or it becomes green but the photo taken is slightly, but noticably out of focus. I can usually tell this is about to happen by the fact that only one rectangle appears, as usually it finds several focus points when it works properly. It seems to have few focus problems indoors as the distances are relatively short (never beyond 50 yards), and it has a focus assist beam. I'm suspecting a lens design problem or a weak autofocus mechanism. Any expert conclusions or suggestions to resolve this problem?

Answer 1

This is going to be a bit speculative, but my sense is that at the mid-zoom range the camera is not getting sufficient contrast from distant subjects. Basically, the system is trying to find distinctive edges to latch onto and is failing to do so as nothing is distinct enough.

At long focal lengths, the subjects are closer and so become distinct. At the wide ends, the distances likely cause smaller things to blend better and create contrast that the camera can latch onto at infinity.

Answer 2

If you have had this problem with three different bodies from the same retailer the problem is likely being caused by one of two sources:

• Poor design. The designers cut a corner somewhere and the system can't quite perform up to expectations due to a limitation of the design. This is not as uncommon with Superzooms as you might expect. Designing a compact zoom lens with a 15x ratio between the shortest and longest focal length involves many compromises to optical quality in order to get that much focal length range.
• Poor Quality Control. If you bought all three examples from the same retailer, then they may have all rolled off the production line during the same batch run. Inspector #9 may have been having a bad day. If this is the case, examples from a different production run may not have the same issue. You seem to indicate in your question, though, that this might be a widely known issue for this camera.

My guess is that the lens design has several elements that move back and forth as the focal length moves from short to long and the issue you are experiencing occurs at a point where one of the elements 'bottoms out' just before or just after it ideally should.

There are a couple of things you can try to work around the problem, but you aren't going to be able to fix it without sending it to a qualified repair facility and there might not be much they can do if it is truly a design flaw.

• For shots that you wish to make using the affected focal lengths, shoot just wide enough that the focus issue doesn't affect the result and then crop the photo to your desired composition.
• Replace the camera with a different model that has better focus performance throughout the zoom range. Read the online reviews for the model you are considering before you buy.