Autofocus

Out-of-camera JPEG.
ISO 2000 | 1/60 sec | F4 | Panasonic Lumix S 24-105mm F4 @ 24mm.
Photo by Carey Rose

The Panasonic S1 uses a contrast detection autofocus system, using proprietary 'Depth from Defocus' technology. This enables the camera to recognize the quality of out-of-focus areas of your image to drive the lens the correct direction to focus on your intended subject. It's very accurate and very quick, but is still behind some phase-detect and hybrid systems used by competitors.

Key takeaways

  • The S1's Depth from Defocus system performs well, though it doesn't track moving subjects as well as competitors with Hybrid AF systems
  • Face detection is effective for eyes, faces, bodies and pets, with a provision to use a button press to cycle through the detected subjects
  • The face detection can still result in false-positives, and sometimes 'loses' subjects just as you want to switch to them, making it hard to use with more than one person
  • The 'flutter' during continuous autofocus is distracting and makes it difficult to see if your subject is actually in focus

AF modes and face detection

There are nine AF area modes available on the S1, and several of them can be tweaked to your liking. The focus mode button, which has a dial for switching between single, continuous and manual focus around it, can be found next to the AF-on button on the rear of the camera.

Just like a pro-grade DSLR you can disable the AF modes you don't use, so that you only need to choose between the options you find useful.

The AF modes include:

Mode Description
Face/eye/body detection Animal detection is optional. Detected faces can be switched by pressing the joystick inward or tapping a subject on the LCD.
Tracking Select a subject via the touchscreen or LCD. The size of the focus point cannot be adjusted.
225-area Your typical multi-area AF mode
225-area (AF-C starting point) Select a single focus point and the camera will use all of the surrounding points to track a subject. This option isn't shown by default and can found in the AF section of the menus.
Zone (vert/horiz) Select how many rows in the frame you want active
Zone (square) Off by default, you can select the number of columns and rows you want active
Zone (oval) You can adjust the diameter of the focus points in the frame
1-area+ Like regular 1-area, but the selected focus point is surrounded by a slightly larger box, to keep your subject in focus if they slightly stray out of the focus area
1-area Standard-issue single-point AF.
Pinpoint A tiny AF point for focusing on things like stars

The face/eye/body detection is impressive, detecting bodies that are quite far away. Compared to its peers, faces and eyes have to be relatively large in the frame to be detected as such, but once the camera has locked on to an eye it tracks it tenaciously, even if the face turns sideways. Pet detection AF is also quite effective.

You can switch between detected people/pets in the scene by pressing the joystick inward or using the touchscreen, but the camera will occasionally 'see' faces in non-human subjects and will intermittently lose and regain detection of others, often making it difficult to effectively cycle to your intended subject. Furthermore, pressing inward on the joystick isn't always reliable; sometimes nothing happens, and at other times the camera thinks you've made a directional press, which snaps the camera out of face / eye detection mode. While the system works for casual use, enthusiast and pro photographers relying on it to quickly target the desired subject in the scene may be disappointed.

Continuous AF

To test continuous AF performance, we first try to shoot a subject approaching at a steady speed using the central AF point. This lets us see how good the camera is at assessing subject distance and whether it can drive its lens to that point quickly. We shot this sequence (and the one that follows) using the Panasonic Lumix S Pro 70-200mm F4 lens at 1/1000 sec, with the aperture wide open and burst speed set to high (6 fps).

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The S1 handled this situation with ease, though it's interesting to note that it lost focus in almost the exact same spot on every run (frame 15 above). The camera would always 'catch up' in the photo that followed.

We then have the subject weave across the camera's AF region in a way the camera can't predict. This has the advantage that the approach rate varies as the subject changes direction. For this test we use the S1's dedicated tracking mode at default settings, selecting our subject using the touchscreen.

Note that the shadows in the sequence below were brightened to better make out fine detail.

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On the whole, the S1 tracked our subject well, both when viewing on the LCD as it happens, and when reviewing the photos afterward. When shooting, the tracking box stayed fixed on the subject as he weaved around the frame. The camera kept up the majority of the same, though it slipped up once or twice during each run (frame 14 above being an example).

AF-C customization

The S1 has four sets of continuous AF sets that you can use as predefined, or customize to your liking. Each of these sets has three options that can be adjusted:

Description Range
AF sensitivity How quickly the camera reacts to changes in subject distance. A higher number will bias the camera toward other subjects that enter the frame. -2 to +2
(Locked-on to responsive)
AF area switching sensitivity How quickly the camera switches to adjacent focus points when the subject moves. Only available in 225-area modes. -2 to +2
(Locked-on to responsive)
Moving object prediction How sensitive the camera is to movements of your subject. Higher numbers are for subjects that change their speed. 0 to 2
(Constant to variable)

The four C-AF sets have the following settings by default:

Set Description AF sensitivity AF area switching sensitivity Moving object prediction
1 Versatile and basic 0 0 +1
2 For subjects that go in one direction at a constant speed +1 -1 0
3 Continue tracking subject, ignoring obstacles -1 +1 +2
4 For subjects that change speed and move unpredictably 0 +1 +2

For the 'weave' portion of the bike test we tried both set 1 and set 4, but did not notice any difference in performance. Even so, it's worth trying out the various settings if you're not getting the results you expect.

Continuous autofocus in use

While the autofocus performance of the S1 is good, the experience of using it can be somewhat disconcerting, at least initially. The DFD focus system, also found on Panasonic's Micro Four Thirds cameras does well in terms of focus accuracy but the user experience in the S1 is rather different.

Perhaps exacerbated by the S1's shallower depth-of-field, its higher-resolution viewfinder and/or its faster lens autofocus communication and movement, the S1's continuous AF looks slightly perturbing through the viewfinder. The intensity of the effect varies with AF area mode but the image you see pulsates as the camera tries to hunt for focus, which can be distracting and make it difficult to concentrate on, and follow your subject. Interestingly, it's better behaved when the camera is set to Face Detection mode, perhaps because the system is more robust and the camera can be more certain that it's focused on the right thing.