Focus Methods, Modes & Areas
Focus Methods, Modes & Areas
By Marc F Alter
Automatic Focus Modes & Focus Areas:
Today’s digital cameras have several different options for how and when your camera will automatically focus. Obtaining a sharp image involves the capabilities of your camera (ie; can the camera automatically focus in low light) as well as making several different decisions. Some of these decisions are based on your Subject (is your subject stationary or moving), some based on your Exposure Settings (effected by Shutter Speed & F-Stop’s Depth of Field), and some based on your camera’s Focus Settings at the time when you take the picture.
For Focus Settings, the first decision you need to make is how you want your camera to focus; Manually or Automatically. Depending on the camera, the setting for this is usually found either on the camera, on the lens, in the camera’s Settings Menu and/or any combination of these.
If you are using Auto-Focus there are several additional settings you must make decisions on so your camera knows how you want it to function. These settings are known as Focus Modes and Focus Areas.
** Some newer more advanced DSLRs have similar functions using different names as well as some additional advanced and/or hybrid auto-focus features. Some examples are:
It is important to note the number of Focus Points is not the only factor in the Auto-Focus calculations but also the Type of Focus Sensors used (See below titled “Types of Auto-Focus Points “).
Note: When 3D Tracking is used in Nikon DSLR cameras, 11 Focus Point are used and the camera uses the Subject’s color to track the Subject. This mode may be problematic when the Subject’s color is the same as other objects and/or background color.
Separating Exposure & Focus (Back Button Focus)
The typical default setting on most cameras is combing Exposure and Focus. For most cameras, you point your camera to your subject, press your Shutter Release Button ½ way down. The camera then determines the Exposure and Focus. You then press the Shutter Release all the way down to take the picture. Using this method, your Subject is Exposed and Focus established with the simple press of the Shutter Release. This method is quick, simple and intuitive. The downside to this approach is that your Exposure and Focus are taken at the same time, causing you to lock your Focus and then recompose for Exposure.
Although this works for many images, there may be times when you wish to separate Exposure and Focus. This is especially important when taking pictures of fast-moving objects (such as birds in flight) or when your Subject and scene Exposure are vastly different. A method to address this situation is called “Back Button Focus” (BBF). This method allows you to use one button (usually a button located on the back of the camera) to Focus and then another button (Shutter Release) to create the Exposure and take your picture.
The disadvantages of using “Back Button Focus” is that it requires using two separate buttons to take a picture which is not simple or intuitive. You will need to “relearn” taking your pictures from using just the Shutter Release to using both the Shutter Release and the BBF Button. The advantages of using “Back Button Focus” however are worth the learning curve. Separating Exposure and Focus Controls allows you to have much better control over both your Focus and your Exposure.
Using BBF is accomplished in the camera’s Settings Menu. Not all cameras have this function and depending on your camera’s capabilities, there may be several different options to choose from. Some of these may include using both the Shutter Release and BBF and/or selecting the camera’s AF-On/AF-Off Button for BBF or selecting another button for BBF. Before deciding to try using Back Button Focus, you should read your camera’s manual and/or watch Internet videos about your camera and its BBF capabilities.
More Information Than You Really Want Or Need To Know
Auto-Focus: How Does The Camera Do This
Today’s DSLR (Digital Single Lens Reflex) cameras are really highly advanced mini-computers, performing vast calculations at incredible speeds. Most DSLRs will automatically change how it performs auto-focus functions based on using either Active or Passive Methods:
Auto-Focus Assist (AF Assist) – A feature on some cameras that helps the camera to autofocus by emitting a light onto the subject so the camera can better detect the contrasts. Usually used during Passive Auto-Focus.
Types of Auto-Focus Points
There are two main different types of Auto-Point Sensors used in most DSLRs; Vertical and Cross-Type. Vertical sensors detect contrast but only on vertical lines. Cross-Type sensors detect contrast on both vertical and horizontal lines. As a result, Cross-Type Sensors are considered more accurate and thus the more Cross Type Sensors your camera has, the more accurate your auto-focus will be. When marketed, a camera’s manufacturer will usually list both the total auto-focus point sensors as well as the number of Cross-Type Sensors (ie; Nikon’s D5 has 153 Auto-Focus Points of which 99 are Cross-Type Sensors. The Canon 1DX has 61 Auto-Focus Points of which 41 are Cross-Type Sensors). Some of the newer Mirrorless camera (ie; Sony a6500 or Sony A7RIII, do not employ Cross Type Sensors).
Keywords: 3D Tracking, Active Auto-Focus, AF Point Expansion, AI Servo Focus Mode, Auto-Continuous Shot Focus, Auto-Focus Single Shot, Automatic AF Point, Automatic Focus, Back Button Focus, Contrast Detection, Dynamic Single Point Area, Focus Areas, Focus Methods, Focus Modes, Focus Points, Group Area, Hybrid Mode, Manual Focus, marc alter photography, marc f alter, Matrix, Metering Modes, mfa images, Multi-Point Focus Area, One Shot AF, Passive Auto-Focus, Phase Detection, Predictive AI Servo AF, Separating Exposure & Focus, Single Point Focus Area, Single-Area Focus Mode, Types of Auto-Focus Points
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