Autoocus Performance and Accuracy
As a professional wildlife photographer, autofocus is one of the most important things that I look for in a lens/camera combination. These days even the most basic lenses offer solid focusing performance, especially when used in good light, but where the top-of-the-line lenses come into their own (along with the better camera bodies) is in being able to focus accurately under challenging conditions. Conditions such as low light, fast moving subjects, and complex backgrounds require lenses that make the most of the camera’s tracking capabilities, and I am happy to report that the FE 100-400mm f/4.5-5.6 GM is more than up to the task.
An important aspect to consider when judging a lens focusing ability is that the camera body plays an integral role in the quality of the autofocus and because of this, it is essential to match your lenses with high-quality bodies that can deliver good focusing performance. I was able to test the FE 100-400mm f/4.5-5.6 GM alongside the incredible Sony Alpha 9 body whose focusing capabilities easily rank as some of the best I have experienced on a professional camera body.
Before I delve into the focusing performance of the Sony lens, I would like to add a bit of context. Currently, the Canon EF 200-400L f4 1.4x is my go-to lens for wildlife photography and using it for the first time was a revelation due to how well it can focus and track moving subjects when used alongside the Canon 1Dx camera body. The Canon lens’s native f/4 aperture allows it to focus incredibly well and I was keen to see how the Sony lens would compare. Heading into this review, I was interested to see if the Sony FE 100-400mm f/4.5-5.6 GM, with its inherent limitations (namely a rather average f/5.6 max aperture at 400mm), would perform in when used under the diverse shooting conditions and lighting found in the mangroves of Rio Lagartos in Mexico. In short, I am happy to report that when paired with the high-performing Sony Alpha 9 body, the Sony 100-400 GM far exceeded my expectations.
The overall focusing performance is superb, with the lens snapping into focus at a very rapid pace thanks to its AF system with one focus group driven by a double-linear motor, and a second by a Direct Drive Supersonic Motor (DDSSM). Initial autofocus acquisition is very fast, and I had no hesitation engaging the focus system the moment the target was in the viewfinder. In good light with a single subject in the frame against an uncomplicated background, the camera and lens would almost instantaneously lock onto the subject, and rarely was there a single frame that wasn’t in proper focus. The focusing accuracy is also very high, and I was blown away by how well it was able to keep track of moving subjects. Paired with the A9 the Sony 100-400 GM has no problem keeping up with fast-moving birds in flight which is something I have found always to be a challenge with even the best zoom lenses.
A big test for the Sony 100-400 GM and Sony Alpha A9 came in the form of the local Black Hawks. Some of the most challenging subjects for our cameras autofocus systems are those that move towards the camera at erratic rates of speed. This forces the camera and lens to make rapid and incremental focus adjustments that challenge even the best focusing systems.
The Hawks have an interesting relationship with the local fishermen who throw them leftover fish which the hawks dive to catch with incredible speed and agility. During the first second or two, the hawk moves in a somewhat predictable manner as it slowly glides towards its quarry. The closer it gets to the fish, the quicker it moves, and by the time it dives down to make the catch the hawk is moving at a rapid pace. The whole sequence takes a mere few seconds and it takes great timing and tracking to follow the action consistently.
In these situations, the Sony combo kept-up with the hawks remarkably well and I rarely found myself missing the shot. Every now and then, the camera and lens combination would lose focus of the Hawk and latch onto the background, but I was impressed with how well they were able to require focus and do so with a great tenacity. Sony’s utilization of two separate focusing motors, with one focus group driven by a double-linear motor and a second by a Direct Drive Supersonic Motor (DDSSM), allows theFE 100-400mm f/4.5-5.6 GM to make very quick focus changes and this design choice really shines when you take photographs of erratically moving subjects. Fluid panning movement is essential when taking photos of fast moving wildlife, and the Sony’s relative lightness in weight dramatically aids in this.
The only situation where I wished for improved focusing capabilities was in very low lighting situations with low contrast. In such moments, the F/5.6 max aperture of the lens proved inefficient at capturing enough light to sustain a strong focusing performance, but one cannot expect such a lens to perform like a fast aperture prime in low lighting situations.
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