With a newfound appreciation for older manual-focus glass through the use of adapters on contemporary cameras, users and manufacturers have been seeking ways to make focusing easier through a variety of different techniques. One of these techniques is focus peaking, an aid that has been very common with videographers and filmmakers, but is just now finding its way into photographers' hands. This is, in part, due to the fact that digital cameras are further blurring the lines between still and video formats.
Focus peaking works by detecting edges of highest contrast in your scene (and therefore most in focus) and highlighting them in a bright color, usually of your choice. This sounds very similar to the contrast detect focusing function found in many cameras and, in a way, it is. The camera will use red, blue, green, white, yellow, or another color that allows photographers to recognize what is in focus and what isn’t, since it will be contrasting with the normal colors of the scene. Also, when using manual lenses stopped down, it can also help show you how much of the scene is in focus at those apertures for checking your current depth of field.
It may sound surprising that this feature has taken so long to make it from video cameras into still cameras, but there is one very important reason: it requires processing of the live image from the sensor in real time and a screen on which to view it. For years SLRs and rangefinders have dominated the scene with their optical viewfinders, but with the emergence of mirrorless cameras and the use of high-quality electronic viewfinders, manufacturers have been able to add numerous features that were not possible with the simple OVF. DSLRs can also benefit from focus peaking through the implementation of Live View and articulating screens that permit composing and focusing using the LCD on the rear of the camera.
While many cameras are starting to have peaking built in and with a few options in the menu, sometimes the implementation is not perfect or not ideal for the user. This can be remedied with the use of external monitors, which can have their own peaking capabilities. The options and settings available on many monitors can sometimes surpass that of the camera, since these units have their own processor, which can handle the job of analyzing footage and outlining edges better than the camera, which has to take care of many more operations at the same time. Additionally, external monitors usually offer larger screen sizes for a larger view for checking the footage and image before you shoot.
Now, one may ask why a tool such as this is necessary, with the high-resolution LCDs and EVFs being released today. This is because as great as those screens are and as perfect as your eyesight may be, being able to see what is in focus quickly and clearly can dramatically speed up your work. Also, it is always nice to get another, perhaps more precise, opinion on the technical aspects before you get home and find out that you barely missed the shot you needed. Peaking also shows up in real time, giving you near-instantaneous feedback as you rack focus through a scene.
Another factor is that new photographers who didn't grow up in a world without autofocus may be hesitant to pick up a beautiful lens if it lacks autofocus. This is an excellent way to get to know a new lens while still capturing your photographs.
Up until now we have been fairly photo oriented, but it is worth considering using peaking in video. Due to the hybrid nature of modern cameras, users who want to take advantage of the advanced video capabilities in still cameras should be aware of this feature. Documentarians and photojournalists will love this, as it will allow them to rack focus and know immediately when to stop while recording scenes where they only have one take. Filmmakers will also benefit by being able to cut down on ruined shots by using the easily seen and repeatable peaking highlights. This can also be used on a director's monitor for checking the shots of the camera operator without hovering over their shoulder.
Peaking isn't perfect however—one thing to watch for is that it may not be clear where the plane of sharpest focus is, such as whether it is the eye or the ear, for example, and when using wide lenses or when stopped down (or both), some cameras will give you peaking highlights over almost the entire photograph. Also, users can be limited by their camera's display, either due to low resolution or small size. There is a reason everyone always says that you shouldn't rely on this screen for checking critical photos. But, as a way to quickly and effectively check focus as you shoot, there is currently no better technique than focus peaking to help you out.