Going to run through a simple but practical tip today--something I've been trying out lately and has been working well. It's about being able to properly focus on your subject when you're using your camera's autofocus system. As I've mentioned before, one of the reasons I prefer using a DSLR over a mirrorless camera is the optical viewfinder. The clarity of the real-time image you see through a DSLR's lens, by way of mirror, cannot be matched by an LCD or EVF, even though those systems let you see exactly what the camera sensor is registering. It doesn't matter if your camera's LCD or EVF has 3.8 million dots; the resolution of reality is only limited by the rods and cones in your eyes. That degree of clarity is a tremendous help with finding focus, with the trade-off being that you don't get the same kind of digital overlay that you would get on an LCD, like edge peaking.
My method for finding focus is a pretty standard one--using the center focus point in one-shot AF mode to find my focus and then reframing the shot to get the composition I want. There are a few reasons I choose center focus instead of full-on autofocus, which may apply to your shooting style. The first is that DSLRs have a limited number of autofocus points. On the Canon 6D, that number is on the low side, at 11. A high-end model like the 5D Mark III has many more (61 points), which makes autofocus much more useful and accurate as a guiding tool. But even with many auto-focus points, not all of them have the same abilities. The autofocus points on a DSLR are phase-detect sensors, but some of them can only detect contrast along one dimension (either vertical or horizontal), while some are cross-type, meaning that they can detect details across two axes. The center autofocus point is also typically the best at doing its job, with the center point on the 6D rated to detect detail at a full stop of lower than its siblings.
Additionally, the array of autofocus points on a camera sensor are usually grouped toward the center of the frame, in a cross-like pattern. You're not going to get autofocusing ability near the edges of the frame, much less the corners. So while you can manually set which specific autofocus point (or grouping of points) to use in a specific shot, that's only going to work if the subject you want in focus is covered by that array. In the simulated viewfinder image below, the auto-AF system wouldn't be able to focus on either of the players' faces, or even the basketball. Even if your subject is withing the AF grid, manually selecting that point can take precious seconds away from the shot, and compromise your ideal composition. By default, DSLRs require that you press the AF Grid button before tapping the directional pad to select your AF point. But even when you turn this off in the camera's menus, I find that it's not as fast as using center focus and then readjusting the framing .
The problem with using the center point autofocus method, though, is that you leave yourself susceptible to losing that focused point through the simple act of reframing.
Here's an example of what I mean. When I use the center AF point to find that initial focus, the part of my subject I aim for is the eyes. I'm a firm believer that the eyes are the most important part of your subject, and a good starting point for figuring out your composition for any given image. In the left part of the image below, I've put the Superman statue at the center of my frame, putting the center AF point right on the figure's eye.
(A side note: when I give my camera to someone else to use--the most common thing they do is frame too high, leaving too much empty space at the top of the frame, since they are keeping their own eyes locked on to the center of the frame.)
Once I have the eyes of the subject in focus using AF, my finger has depressed the shutter halfway, locking the focus plane into place. I then typically angle the camera down, recomposing the shot to put all the elements of the subject I want into its place. The right side of the image in this case represents how I would frame a subject like a cosplayer. The whole process, from locking AF to re-framing, honestly takes about one second. I'm often doing this in a hurry.
(A second side note: while this act of locking AF and re-framing has become second nature, it can still catch some subjects off guard. In the case of photographing female cosplayers, it can unfortunately give the impression that I'm cutting off their heads and just taking a photo of their chests. You get a sense of when someone might feel this way and give them reassurance by offering to show them how the photo turned out immediately after taking it.)
But in reviewing some of my older photos, I've noticed that upon closer inspection, the eyes of my subject are actually out of focus, even though the whole point of the center AF method was to get their eyes as sharp as possible. The image below shows a close-up crop of the re-framed photo. Superman's eyes are clearly outside the focus plane. In fact, his entire head is out of focus here. It's not something you can necessarily detect in the viewfinder, either, and especially not on a small LCD without zooming in when reviewing the image.
This happens because the very act of angling the camera down to re-frame your photo shifts the plane of focus away from the original point. As I wrote about last time, you have to think of focus like an invisible plane cutting through space, running parallel to your camera lens and sensor. The diagram below illustrates how that plane slices through a subject's face when the camera is aimed at their eyes.
When you tilt the camera down, that focus plane doesn't stay static. It moves along an arc, corresponding with the degree to which you angled the camera. Once again, the diagram below does a good job illustrating how the focus plane is tilted back when the camera is tilted down. So when the lower body of your subject becomes the center of the frame, the focus plane may be angled such that their eyes and head are moved out of it--in this case in front of it.
One solution is to re-frame your shot by moving the camera laterally--perfectly up or down to keep the lens parallel to the subject. This requires bending your knees down to frame down, or lowering the camera down using your elbows. This is pretty tough to do without losing stability--you typically want to keep your elbows tucked in close to your chest and locked.
The other solution, which is what I've been practicing, is to keep the center AF and tilt to re-frame method, but learn to adjust the focus ring on the lens ever so slightly after re-framing, and to do so from muscle memory. After a couple hundred shots, what you begin to learn is approximately how much you have to turn that focus ring (clockwise on Canon systems, counter-clockwise on Nikon systems) to draw your subject's eyes back into focus. For the amount of tilting I do to re-frame, it's about half a centimeter of turning (juuuussst a little) the ring before I take the shot.
So now, my muscle memory has one more step. I center up the shot on the eyes, half-press the shutter and hold, re-frame down, and give the focus ring a very little twist. Snap snap snap. Just to be safe, I twist it ever slightly so slightly more and snap a few more shots just to be safe. Then I'll review the sequence of photos taken and save the one that has the eyes the most in focus. The comparison shot above shows me doing exactly just that, with the photo on the left being a close-up of the head without the micro focus adjustment, and the one on the left being after. The trick is to really be able to know how much to twist that ring without even looking directly at the subject's eyes--I'm thinking more about composition at that point--the tweaking is all muscle memory from practice.
What are your focusing methods and tricks? I'd love to hear them in the comments below!