In theory focusing is very simple. You point the camera, you wait for the focus confirmation, and you take the picture. But as we all know things don’t always work that way.
Achieving focus is somewhat arbitrary in the sense that it is dependent on many factors, starting with depth of field.
Depth of field can be tricky to understand. We talk about depth of field with the implication that the point of focus has depth when the point of focus is literally at a point, it has no depth. The reason we say, “depth of field” is simply a short hand way of saying “the area of the light cone that appears to be in focus”. Appears is the keyword here because “appears” to be in focus can mean different things depending on the camera sensor, the print resolution, the print size, and the print viewing distance.
For instance, if you view photos on a phone the “depth of field” is drastically larger than if you view the photo as a 16×20 print. This is simply a matter of detail being hidden the smaller an image is. You can test this in your favorite editing application. Open a picture that is slightly out of focus and zoom out until it appears sharp. Now zoom in to your image and blow it up until it appears to fit 16×20, does it still look sharp? If not, then it obviously isn’t good enough to be printed at that size.
All this means “depth of field” is generally relative to the size of the print. So, when determining if something is in focus or not think about the media you are targeting. For instance, if you’re targeting Instagram, you can get away with a slightly out of focus image that you wouldn’t get away with in a larger print or on a large desktop monitor.
To understand more about depth of field check out my quick tip: How to control depth of field.
All this is well and good but what is good focus in practice? Generally, the subject of your photo should be in focus, no matter where it is in frame. If you’re really close to your subject and have narrow depth of field you should try to get a prominent feature of the subject in focus, typically with people this would be the eyes. If you don’t focus on the eyes your photo might be in danger of being called out of focus.
Adjust your viewfinder
Make sure that when you first look through the viewfinder the image you see appears sharp and in focus. If your eye has to adjust to the focus when you look through the viewfinder you need to adjust something called the “diopter”. Doing this may be of particular importance for people who wear glasses as the glasses will force your eye to be further from the viewfinder thus requiring an adjustment with the diopter. Check your camera manual to find your diopter adjustment, it is usually right next to the viewfinder on modern cameras.
Be still when focusing
To achieve focus you need to be careful, especially with a wide aperture lens. Remember the plane of focus is literally a 2D plane, it has no actual depth, if you move a millimeter that plane moves a millimeter out of focus on your subject.
If you’re using ONE SHOT AF what you should do is frame your shot with your focus points on the subject, then hold still, then focus, then immediately take the picture after the camera achieves focus.
For a lot of you the true progression of events is probably more like, change framing to get focus points on face of subject, get focus confirmation, carefully reframe the subject, then take a picture.
If you’re doing anything after you get focus confirmation, even if its just waiting too long, which can cause your body to sway unconsciously, that is probably why you’re messing up your focus on your shots.
The rule for being still applies when using SERVO AF as well. The reason is that modern cameras use algorithms that work to anticipate where the subject will move to next. If you are moving all over the place you are just complicating what the algorithm has to understand. Hold still and the camera will have an easier time tracking your subject.
Frame your shot wider
One aspect of a lens you can exploit is how depth of field relates to focal length. With all lenses the plane of focus is a 2D plane or point. There is no depth. But, depth can be simulated by reducing the rate of fall off from the plane of focus. One way to do that is to use a wide angle lens. Say you are using a 24-70mm lens, if you zoom out to 24mm that will reduce the fall off from the point of focus which in effect increases the “depth” of the area of the image that appears to be in focus. Not only will you find it easier to frame your shot this way, but you also increase the depth of field which makes getting focus that much easier.
Use a smaller aperture
Another way to reduce the fall off from the plane of focus is to use a smaller aperture. Go ahead and push it all the way to f/11 if you have to. If your lens has a very long focal length even f/16 could still be useful. Of course, all this assumes you are shooting 35mm or “Full Frame” digital or film. If you are shooting medium format, you are probably well aware that you need to stop down your lens a LOT to get decent depth of field.
Use a different focus mode
Another option for your focus is to use SERVO instead of ONE SHOT. Most advanced cameras have the ability to track a subject using something called SERVO mode focusing. In SERVO mode instead of attaining focus then stopping, the camera will continue to adjust the lens for focus even as you move or your subject move ever so slightly. For static subjects SERVO is unnecessary and may actually result in ever so slightly missed focus, so be aware of what your camera is capable of when choosing the correct focus mode.
Use subject detection like face and eye-detection AF.
If your camera supports it, using face or eye-detect AF can greatly improve results when shooting people and animals. Of course these types of focusing modes make adjusting your focus points a thing of the past. Most of the time using SERVO AF is going to be your best bet when shooting people and animals as they rarely hold perfectly still. Canon cameras like the EOS R5 and EOS R6 support focusing on people or animals.
Use the appropriate shutter speed
Another mistake new photographers make indoors or even outdoors on a cloudy day is underestimating how dark it really is. What happens is we accidentally lower the shutter speed until the camera says the picture is exposed correctly without paying attention to what the shutter speed actually is because we are assuming that everything is ok because it looks ok in the viewfinder. The problem is that if your subject is moving you will need at least 1/160th of a second to get a sharp picture. And lens stabilization will not help with subject movement, it only reduces camera movement.
What you need to do in order to get the higher shutter speed indoors is increase your ISO speed. Most of the time when you are indoors you will need an ISO in the range of 1600-3200 to get a sharp picture of a moving subject even with a “fast” f/2.8 lens. If you have a slow lens say f/4 or slower then an ISO as high 6400-12800 may be required for a sharp picture in typical indoor light.
On most modern cameras made in the last couple of years the penalty for using a high ISO is minimal so you might even be ok just setting your camera to use “auto ISO” and choosing a manual shutter speed of about 1/160th of a second.
Use a flash to stop motion
One advanced use of a flash is not simply to add light to your scene but to also stop motion. This is the pro’s way of getting sharp pictures in indoor scenes where people are moving around. If you adjust your camera settings to produce a relatively dark exposure, then use a flash to light your subject, the instantaneous flash of light from the strobe will effectively stop the motion in the view of the camera. To learn more about doing this check out this article on using camera flash to stop motion. The really great thing about doing this is that the flash of light will stop the motion regardless of the shutter speed but only if the exposure without the flash would be dark. For instance, if the exposure without flash is dark, and your shutter speed is 1 second, the flash will produce a perfectly sharp image despite the slow shutter.
Have any other tips for achieving perfect focus? Let us know about it in the comments below!