At the time of this writing, the Leica product page for the SL states that the 'SL-system marks the beginning of a new era of professional photography,' offers impressive performance including 11 fps burst shooting, and the 'fastest autofocus of all professional cameras.'

Obviously not all professional systems are built for speed, but this seems to be something Leica is touting with regards to the SL; let's take a look at how its general performance and autofocus stack up. 

The system

So, does the SL offer the 'fastest autofocus performance of all professional cameras?' In a word: no. Is it still usually very fast? Yes, with the right lens. It's also usually very accurate (as we'd expect from a contrast-detect system), and during burst shooting, comes with a high hit rate.

The system isn't perfect though; even with an autofocus point over a slow-moving boat at a distance, the SL front-focused slightly. Processed and cropped to taste. Vario-Elmarit-SL 24-90mm F2.8-4. ISO 50, 1/640 sec, F4. Photo by Carey Rose

The contrast-detect system on the SL is similar to the 49-point system on the Q, though in 1-point mode, you have access to a whopping 529 points. There are still some confusing interactions between the Focus Modes (AFs vs AFc) and 'AF Modes' (Static, Dynamic [Tracking], and Auto with face detection) as on the Q. You can then choose whether you want to autofocus using a single pinpoint, a slightly larger field, or an even larger 'zone.' Touch-to-focus works well as far as moving your AF point around on the screen, but the screen can't be used as a 'touchpad' to do so with your eye to the finder.

Leica was unfortunately unable to loan us their Vario-Elmarit-SL 90-280mm F2.8-4 so we were unable to put the camera through our standard testing, but we were able to get some overall impressions with the other lenses available. The 24-90mm F2.8-4 in particular is usually as fast as a fast-focusing lens and phase-detection system, but will sometimes go through more of a contrast-detect hunt than you might expect (sometimes hunting the wrong direction first, as opposed to Panasonic's Depth-from-Defocus system, which rarely shows such behavior).

Here's a wide-angle, wide-open close-up exercise using the SL's Dynamic (Tracking) mode, where initial acquisition was on Dan's face.

In Dynamic (Tracking) mode here, the SL puts up a good show. Unfortunately, initial acquisition of your subject can be a bit spotty; a half-press of the shutter, even when your AF point is over a subject with sufficient contrast, will occasionally see the SL throw you a red box, and it won't even attempt to focus at all. Once it does start tracking, performance is very good, but for more crucial moments, we'd recommend avoiding it.

If there is a further downside to autofocus on the SL, it's that the system's speed is incredibly lens-dependent. Autofocus on the Summilux-SL 50mm F1.4 is painfully slow. Absurdly slow. The lens is also crazy-sharp, but don't expect to be shooting much in the way of moving objects with it.

In lower light, autofocus speeds drop somewhat, with the lens often needing to go through a full hunt (or two) to acquire focus. In dim light, the focus will simply fail to find focus where equivalent DSLR systems will lock without problem. If you're doing any shooting in failing light levels, it's best to switch to manual focus.

Even though Mochi's not the fastest beagle out there, I had to wait until she was about to nap to get her to hold still for long enough to allow the Summilux-SL 50mm F1.4 to nail focus. Processed and cropped to taste. ISO 4000, 1/100 sec, F1.4. Photo by Carey Rose

Autofocus in video

The Leica SL offers a good 4K video mode from a 'Super 35' crop of its sensor. Autofocus performance has improved over previous Leica cameras that shot video, like the Q, but is still 'not quite right.'

In the Auto (Face Detection) AF mode with continuous autofocus enabled, the SL does fairly well, re-focusing smoothly at a decent rate without too much hunting as the scene changes - though occasionally, it will incorrectly hold a scene out of focus. Single point and tracking continuous autofocus, on the other hand, exhibit lots of hunting, and require you to half-press the shutter in order to activate them during recording, which isn't very practical.

The sum-up

So, overall, the SL is a fairly responsive camera that is capable of great autofocus performance in good light, but has its fair share of quirks. Beware of occasionally unreliable Dynamic (Tracking) autofocus behavior. Know that for your hard-earned five thousand dollars, the Summilux-SL 50mm F1.4 will blow you away with its optical performance, before sucking the wind from your sails with atrociously slow autofocus. Shooting moving objects in low light will prove a challenge. If you're shooting video, the 'Auto' AF mode works well for casual clips. If you can work around these limitations and caveats, the SL will serve you well.

Skate on; our informal impressions of the autofocus system are largely positive. In straight on 7 fps runs, we had almost perfect hit-rates at 90mm F4, save for when Dan got too close to the camera. Out of camera JPEG cropped to taste. ISO 50, 1/500 sec, F4. Photo by Carey Rose