If you’re consistently struggling with poor auto-focus performance and want to know how you can improve, this video from Steve Perry is a treasure-trove of ideas that you can use. A camera’s auto-focusing performance depends on a number of aspects and any one of them can throw it haywire:
1. The Lens Needs to Be Calibrated
If your lens is consistently focusing in front or back of the intended point of focus, your lens needs to be calibrated. Relax. This is not something really serious and it can be adjusted pretty quickly. Some cameras come with a built-in process to recalibrate your lens for that particular camera-lens combination. This is known as AF fine-tune or AF Micro Adjust feature. There are other off-camera options such as LensAlign and FoCal.
2. Dirty AF Sensors
When we talk about sensors we only refer to the main sensor that sits behind the mirror. There is another set of sensors that are located at the base of the camera. These are your AF sensors. Dirty AF sensors can impair the ability of your camera to focus precisely. This problem is compounded when you’re shooting in low light or low contrast subjects. It is a good idea to periodically clean your sensor when your camera is consistently front or backfocusing. To do this set your camera to Sensor Cleaning Mode. Then use a manual blower to dust the AF sensor.
3. Wrong AF Mode
One of the most common problems for consistently not getting a sharp image is that your camera is set to the wrong AF mode. E.g., if you are photographing birds and you seem to be getting blurred images all the time check the active AF mode. If it is anything other than AF-C (or Continuous Servo AF) you’ve got a problem. The same way, if your camera AF area mode is incorrectly set you are going to have problems.
4. The AF Point Outline is Off
You know those red or yellow AF points? They’re not always consistent with where the AF point is actually positioned. It can sometimes be not quite at the place that the guide seems to point at. That means when you rely on the AF point, your focusing is going to be off.
5. Heat Refraction
If it’s a hot and sunny day you could actually be fighting heat refraction. When warm air rises up, it mixes with the cool air above and that creates a difference in air densities. This makes the auto-focusing system of your camera go haywire. This problem affects telephoto shooters more than wide angle shooters. There’s rarely a solution to this problem except that you need to find a spot where the ground between you and your subject is cooler.
6. Dirty Lens Contacts
The contacts between your lens and your camera channel information back and forth between the lens and the camera. If they’re dirty, their ability to lock focus accurately is impaired.
7. Poor Technique
If your technique isn’t precise, you’re going to get image blur or out of focus results nine out of ten times. Poor technique could be anything ranging from using a slower than optimal shutter speed to an inaccurate tracking movement or nonwillingness to use a tripod—or even incorrect breathing when shooting.
8. Tough Subject / Wrong Sensor
Tough subjects and incorrect sensor choice can be a frustrating mix and result in poor auto-focusing performance. The center AF point on your camera is usually the most sensitive and has the maximum amount of technology packed into it. As you move more and more away from the center AF point, you’re going to find slower and more unreliable performance. Plus, when shooting in low light and low contrast subjects you will find this problem is compounded together with the incorrect sensor choice.
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