Low light AF performance

It's often been the case that on-sensor AF cameras have seen their performance drop significantly when light levels do: particularly ones that rely heavily on contrast detection. Our experience has been that the a7R II does a fantastic job of maintaining its AF performance in low light, as long as you pair it with bright lenses. So we put the a7R II to the test, and the results may surprise you, as they certainly surprised us: the a7R II paired with a F1.4 lens was able to keep up with the best DSLRs, continuously focusing at -2 EV even using portions of the frame unavailable to DSLRs. Click here to read about those experiences in more detail.

In the video below, we show and explain our test where we compare the low light continuous AF performance of the a7R II with that of the Nikon D750 and Canon EOS 5DSR, all of them using wide-aperture lenses.

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As should be apparent, the a7R II is actually able to refocus more reliably in low light than its DSLR peers. Again, this performance is dependent on the lens used, though: the brighter the lens, the better the performance. DSLRs don't have this dependency, so if you're shooting at, say, F4 in the very dim light, you'll fare better wht a DSLR. But pair the a7R II with a bright lens, and you may be pleasantly surprised. Note that in AF-C, you'll want to keep your aperture wide open, as the a7R II, despite opening up the aperture initially to acquire AF, will focus stopped down at your shooting aperture thereafter. A slower f-stop will cripple the AF system in low light.

Eye-AF

The a7R II includes the Eye-AF system that impressed us so much on the RX100 IV. Using it requires you to assign it to a custom button, at which point, holding down the button takes priority over the currently-selected autofocus area mode.

By default the system will select the eye on the face closest to the camera but if you're using an AF area mode with a specific AF area selected, it will track the eye of the face nearest your chosen AF point.

Once selected, in AF-S mode the camera will find and lock focus on an eye, but the feature really comes into its own in AF-C mode, though, with the camera constantly trying to maintain focus on the subject's eye - regardless of any movement between the camera and the subject.

The implementation is really clever but not without a couple of odd quirks. For instance, if you've selected one face out of several, then your subject looks away or closes their eyes, the camera will jump to another person and will stay stuck on that person.

This video first shows how quickly the camera can refocus as the subject distance changes. It then shows just how tenatiously the camera will stick to one of the subject's eyes, in EyeAF mode, despite the fairly fast, unpredictable movement and the rather poor lighting in which the test was conducted.

The final section of the video shows what happens if you then engage continuous shooting. The images the camera shot are arranged in the following rollover. This is probably the weakest performance we've seen but makes clear how EyeAF is very good but doesn't always result in a perfect hit rate.

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Overall though, the story is very similar to the one we saw with the Lock-On AF modes: the camera is incredibly good at identifying and following a subject but doesn't seem able to do both this and shoot continuously (though in most attempts got better results than this). The final section of the video above shows the degree to which the performance drops if you try to use continuous shooting.

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As such, the best results are achieved by letting the camera keep track of the subject, then chosing your moment to grab the shots you want, one-by-one rather than as a burst. The rollover above should make it clear how successful this can be - a good run of critically sharp images despite the camera being used close-up at F1.4. You'd be hard pressed to even use a DSLR in this manner, having it subject tracking to continually keep the eye of your subject in focus. Nikon's full-frame 3D tracking comes close, and is really the only DSLR technology that can compete, yet still requires you to first define where the eye is - which can slow down shooting, particularly with erratic subjects and when it comes to capturing candids in-the-moment.


Quick Tip: Alpha 7R II AF Setup

With all these AF options, it can take a while to find a way of shooting with the a7R II. Watch the short video above to understand our preferred setup for robust AF across many shooting scenarios. Briefly, we set our camera to:

  • AF Drive Mode: AF-C
  • AF Area Mode: Lock-on AF: Flexible Spot
  • Assign Eye-AF to a custom button (We use C3)

This way (for most shooting) you can simply point at your subject (be it human or not), half-press the shutter button and recompose your shot, fairly safe in the knowledge that the camera will maintain focus on your selected subject.

For portraits and people photography, you can just compose as you please and hold down Eye AF, trusting the camera to find a prominent face in the scene and focus on it. What's great about combining AF with a Flexible Spot or Center mode is that the camera will prioritize faces near your selected AF point. This allows you to select preferred faces on the fly: place the AF point over your desired face, press Eye AF, then hold down Eye AF as you recompose. From now on, as long as you keep Eye AF held down, the camera will stick to that person's eye like glue. But in case you don't have time to 'focus-and-recompose' like this, just holding down Eye AF will at least still focus on a face in the scene, even if it happens to be well outside your AF point. This makes the system a boon for candids.