Autofocus
Like the Alpha 900, the Alpha 850 has nine user-selectable AF points, with a further ten supplementary points that cannot be manually selected. The central point has a dual cross sensor for added sensitivity.
Although the 3fps maximum continuous shooting rate may not lend the Alpha 850 to sports photography, most enthusiast photographers want a camera that can be put to a variety of uses. In reasonable light conditions the Alpha 850’s AF system is swift and decisive. When shooting a local rugby match under a heavily laden sky, the less-sensitive peripheral AF points were a fraction slower to pull the subject into sharp register than the central point, but I didn’t experience much hunting when using the continuous AF mode.
Although there are three modes available for selecting the AF area to use – Wide, Spot and Local – there are very few occasions when I would use the Wide option. This method allows the camera to select any of the 19 available AF points and takes control away from the photographer. With team sports such as rugby, it tends to latch on to the nearest potential subject – another player or referee, perhaps – rather than the real point of interest. It could, however, be useful when photographing subjects such as birds, which move unpredictably against a clean background.
In its Spot mode, the AF point is locked to the centre. While this may be useful on occasions, it makes more sense to use the Local option, which allows the user to select any of the nine available AF points using the mini-joystick multi-direction controller. A quick press of this is enough to select the central AF point. I found this controller within easy reach of my right thumb and have no problem selecting the appropriate AF point when the camera is held to my eye.
When light levels fall to the point when the maximum sensitivity setting (ISO 6400) is required to allow movement-freezing shutter speeds (and on an overcast day at this time of year that seems to be around 3pm), the Alpha 850’s outer AF points become too slow to use when shooting action so it’s best to stick with the central point. In its continuous mode it does a respectable job of keeping up with the action provided the selected AF point is kept over the subject.
