Modern DSLR cameras have all sorts of modes and options for getting just the right picture. Almost all have some in-body autofocus system which allows the photographer to simply shoot while the camera focuses. Lenses also come with motors built inside to make the process even easier. Getting things focused is an essential part of having a sharp, in focus image. Blurry and unfocused images rarely turn out looking good and even converting to black and white (an old trick) can’t save them. If you can get your focusing correct then you’ll be more likely to have sharper and better images. Having “creative blur” is nothing more than an excuse for poor focus when you’re not doing it on purpose.
Autofocus often depends on the type and brand of your camera, while most of the terms are the same the menu systems are not. This is based off of the standard Nikon menu system.
How Autofocus Works
Digital photography is very forgiving because you can tell instantly if a shot is in focus and try it again if it’s not. Back in the days of film a photographer had to manually turn the lens casing to adjust the elements inside so that everything was in focus. Now you can press a button and the whole system whirrs together until everything is focused and exposed for you.
Active or Passive Autofocus
There are two types of autofocus – active and passive. Active autofocus works by shooting a small red beam onto your subject which bounced the light back so the camera can figure out an estimate of the distance between you and the subject. Once it has that number it automatically adjusts the lens to focus based on that. It works well even in poor lighting but is limited to 15-20 feet. Passive autofocus works poorly in low light while active autofocus will only work on subjects that are still and unmoving.
Rather than using a red beam, passive autofocus uses special sensors inside the camera body to detect the amount of contrast on the subject. It uses something called phase detection which looks for the sharpest part of what it can focus on. If there isn’t enough contrast then the camera will continue to focus until it finds it. The problem with this is that any time you don’t have a lot of contrast (eg poor lighting) the camera can try and focus ad infinitem and still not get a grip on the subject.
Some speedlights also have an AF Assist function which allows the light to be used in place of the beam by lighting the subject better so the camera can see the contrast. It still uses the same passive autofocus and is not a beam itself.
Most DSLR cameras have the ability to use both active and passive autofocus and while contrast detection is more accurate than phase detection it can be quite slow. Most high-end cameras combine the two effortlessly so that they use contrast in low-light shooting and phase detection when the light is good. There are some models which include the phase detection points on the sensor for better accuracy since you know what your camera is focusing on.
If you look inside your viewfinder you’ll see little dots or squares in a pattern on the glass. These may vary by brand and level for different types of focusing systems with the entry-level ones having simpler and less focusing points which have only minimal adjustment options. A pro level camera may have 20-50 different focusing points which can be configured in a variety of different ways. These are all part of phase detection and are used to detect contrast. The number of focusing points is extremely significant because it relates to your camera’s ability to track a subject in motion, and which areas of the image can be in focus at the same time.
There are different types of focus points – vertical and cross-type. The sensors for both are different which is why having numerous focal points is important to create a sharp image. Vertical sensors are only able to detect contrast in a one dimensional, vertical line while cross sensors are able to use both vertical and horizontal lines and are two dimensional. Obviously cross-type sensors are much more accurate so having a greater number of cross -type sensors means better focus. For Nikon cameras this is listed under key features with the number of focal points and how many cross sensors together. The number usually specifies the total number of focus points, and how many out of it are cross-type. It’s important to look at just how many of these AF points there are, especially if you plan on shooting motion like sport or wildlife images.
Most cameras have different focusing modes which are helpful for beginners or specific situations for example portraits vs sport motion. When using autofocus for a still subject generally you will half press the shutter to acquitre focus then take the picture and if it doesn’t work repeat the process again. With sport or in motion images you haven’t got time to do that so you need a focusing system that is continuously moving with your subject. DSLRs generally have built-in settings to do this. There are four auto focus modes found in DSLRs.
Changing focusing modes is usually done through the Info or Menu screen while more high end cameras have a dedicated switch or button which changes modes. There will also be an option to Manual focus either on the body or on the lens as well.
Single Area AF/One Shot AF
This is the most straightforward type of focus, you pick the point, half press the shutter, and the camera focuses. If you or the subject moves you will have to repeat this even if you do not let go of the shutter button. The focus is locked and remains so which may stop your camera from taking the picture if the focus is lost. Some cameras have an option in AFS mode to ignore this setting and release the shutter anyway. If you have a speedlight that has AF assist then it needs to be in the same mode and also has to have an AF assist red beam to work properly. This is best for low light situations.
Continuous focus is the opposite of this. Once you half press the shutter the camera continues to follow your subject and maintains focus as the subject moves. It’s entirely automatic and readjusts as necessary as long as you continue holding that shutter or autofocus button. It can also be used for tracking multiple focus points. Most photographers shoot in this mode and only change as needed.
AF-A/AI Focus AF
This is a hybrid mode that isn’t found on all cameras and it switches between continuous and single area focus. The way this works is that the sensor detects either a stationary or in motion subject and switches accordingly. This is the default mode on lower end DSLRs and it mostly for beginners who aren’t yet comfortable switching modes.
This is a newer mode that is specifically for video and live view. It automatically tracks movement and keeps focus during video. It’s too slow for most fast subjects but will work for most users who want to record video with a DSLR.
AF Area Mode
Some DSLRs also have AFA mode which allows the user to choose a specific area in the viewfinder where the camera should focus. There are several different types of area mode focusing.
- Single point area focusing means that the camera only uses one of the focus points and will only use that one even if you move the camera. This is best for landscapes.
- Dynamic auto focus means that the camera still uses the single point but it can also track subject motion so it can automatically switch to a nearby focusing point as it tracks the subject. There is usually no indication inside the viewfinder that the focus has changed. This is better for fast moving subjects and on higher end systems you can specify more than one point to track (up to 50 in some cameras). However, if your subject moves away from the selected focusing points the camera will no longer be able to focus anymore.
- Auto Area auto focus is essentially a point-and-shoot version where the camera automatically picks the best focal point and while user operation is simple the mode itself is so complicated that with a good sensor it can track different skin tones in a face. If you’re using auto area you can half press the shutter and then use back button focusing to retail those focal points or release and half press again and the camera will pick a different location to focus on.
AFA modes can be combined with other focus modes and may also have specific features like face detection, wide area, and tracking subjects. These are all camera specific and even brand specific like Canon’s “Spot AF”.
Group Area AF
This works similar to the AF-s mode but the camera can pick 5 or more focal points to track a subject and is great for narrowing in focus or for smaller, erratic, subjects with more consistency. All focus points are activated simultaneously while the camera tries to find the point with the best contrast. This is similar to Dynamic 9 focusing, however D9 uses 8 focus points instead of 5. It uses the closest subject and does not give priority to any specific focal point out of those 5.
Generally photographers will tell you that the more experienced use manual focus only, but their settings in the camera still rely on much of the information the autofocus system provides, even if they are manually adjusting the lens. Here is a cheat sheet of what to use for various situations:
|Situation||Autofocus Mode||Autofocus Area Mode||Custom||Custom|
|Outdoor Sports||AF-c||Dynamic AF or Group Area AF||Dynamic AF 21/51 points||AF-C Priority Release & Focus|
|People Outdoors||AF-C, AF-S or AF-A||Single Point AF||AF-S Priority Focus||AF-C Priority Release & Focus|
|People Indoors||AF-s||Single Point AF||AF-S Priority Focus|
|Birds in Flight||AF-C||Group Area AF or Dynamic AF||Dynamic Area 9/21 points||AF-C Priority Release & Focus|
|Landscapes||AF-S||Single Point AF||AF-S Priority Focus|
Focusing In Poor Light
Using the center focus point will often give you the best chance of getting clean and sharp focus. Make use of the AF assist on your speedlight if you have it for the same reason. Try to find a focal point that has good, sharp contrast rather than a plain object and create more contrast by adding lights or improving the light. You can also use live view contrast detect or manual focus if necessary to get things perfect. Sometimes manual focus is even quicker than messing with all these settings and having to change them between shots. Many landscape and architecture shooters only use manual for this reason.
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