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Troubleshooting Focus
Your camera has autofocus but your pictures are not really sharp. What is wrong? There are only a few places to look for errors, and a systematic approach will usually solve the problem. Let’s start by eliminating the possibility that the pictures actually are sharp, but you can’t see it. How could that be? If you look through the viewfinder and judge the image to be blurred, there are 4 possible reasons: 1. You haven’t pressed the shutter button: cameras do not focus until you depress the shutter button. This is a 2-stage process. Press part way and the lens will focus on the subject. You should hear or see a signal confirming focus, after which you can complete pressing the shutter release to take the shot.
2. Your viewfinder is not adjusted for your eyesight: many cameras incorporate a dioptre adjustment to let people with glasses see without them, or see with the particular lens they prefer (bifocals can be tricky) or simply to let anyone get the sharpest view through the viewfinder. It is easy to knock this control out of adjustment. Make sure it is adjusted for your sight by looking through the finder while turning the adjustment wheel, usually found beside the viewfinder.
3. Your eye is too far from the viewfinder: spectacles, including sunglasses can prevent you seeing the viewfinder properly, and can also make it harder to align your eyes with the centre of the finder; this may make it look like the image is blurred when it is not.
4. Fog, mist or grease on the viewfinder of LCD. Wipe it carefully with a dry, lift-free cloth. In all of these situations, the image will be sharp when viewed or printed, because the optical path is not affected. If the printed picture is blurred or soft, the solution is elsewhere. 1. Mist on the front of your lens or between lens and filet, or condensation on the rear of your lens or on your mirror should be left to evaporate naturally. Trying to dry these surfaces is risky: They are easily damaged. If you have a UV filter in place to protect your lens, dust it with a brush, then dry with a soft cloth.
2. Autofocus has been turned off: Many cameras give you the option of focusing manually. If the manual focus has been engaged, you may not notice much difference in bright conditions with distant subjects, because small apertures give a lot of depth of field. As the light falls and distances decrease, focus becomes increasingly critical. Check to see if your camera has an autofocus switch and that it is in the right position.
3. Your camera has focused on the wrong point: cameras detect correct focus within a small area of the field of view. The default is usually the centre of the picture. If you want something off centre to be in focus, you need to focus on that point first; then, still holding the shutter button down half way, recompose and complete the shot.
4. More advanced cameras let you choose between a number of different focus points. If you have the “wrong” one selected, reset to the appropriate one. If your model uses eye-detection to figure out which point to focus on and is getting it wrong, recalibrate or disable it. Autofocus is achieved by judging the contrast levels within the autofocus sensor area. If your subject is low in contrast or if the light levels are low, it might struggle to find focus. You can improve your chances by focusing on a higher contrast area. For instance, you may not be able to focus on a grey cloud, but you might do better if you focus on the point where the cloud meets a patch of blue sky or whiter cloud. Low light levels are often also low in contrast and benefit from a similar approach. Most cameras focus at full aperture. Long lenses with small maximum apertures can be harder to achieve focus with, and adding a televerter or extension tubes may defeat the system altogether: switch to manual in these situations. Where depth of field is very shallow, very small movements in the camera or the subject will cause autofocus to “hunt” as the point of focus changes. Keeping just the part of the picture you want sharp is difficult. Again, switch to manual focus, and focus by moving the whole camera, or the subject, rather than trying to adjust the lens. Finally, many people correctly focus on their subject by partly depressing the shutter button, but then sway a little in or out before completing the shot; or the subject moves a bit before the photo is taken. Make sure that you do not move once focus is achieved.
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The copyright for this content entitled "Troubleshooting Focus" has been specified by the contributor as:
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This intel was contributed by David Rich
David Rich
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May, 2012
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