Olympus OM-D E-M1 review – Autofocus
Images: Shot using the Zuiko 50-200mm f/2.8-3.5 ED SWD four thirds lens with the MMF-3 adapter, the phase-detection AF of the E-M1 did a good job of keeping focus on the horse’s head over this sequence of five images
Despite the Olympus E-M1 having a sensor capable of phase-detection AF, the feature is only employed when using four thirds lenses via the MMF-3 adapter. When using standard micro four thirds lenses, the camera relies on the standard contrast-detection AF.
When we first saw contrast-detection AF used in compact system cameras a few years ago, focusing was noticeably slower than the phase-detection AF we were used to seeing in DSLRs. However, in the past year or so, things have changed quite dramatically. No longer is contrast detection the poor relation of phase detection AF, and many CSCs actually have contrast-detection AF that is faster, in some conditions, than the phase-detection autofocus found in DSLRs.
Indeed, the Olympus OM-D E-M1 has an extremely snappy contrast-detection AF system. If you look at the way the camera focuses the lens, you can see exactly how focus is acquired so quickly.
The AF motors operate at a very high speed to find the highest point of contrast. However, to do this, the focus must go slightly beyond this point to know exactly where the contrast peak is. Once the AF has quickly established that it has gone beyond the contrast peak, the AF motor slows down slightly and reverses back to the correct point, which is the point of focus. All this happens in a fraction of a second.
In total, there are 81 selectable AF points on the E-M1. These can be selected at a standard or small size, or a group of nine areas can be selected, which is useful if you are trying to focus on only a small area of the frame – useful for wildlife or portrait photographers, perhaps. Portrait photographers may also be pleased to hear that the E-M1 features face-detection AF, which is capable of detecting the subject’s eyes before focusing on the one nearest to the camera. That’s great for professional photographers, but also for amateurs wanting the sharpest images.
