When you're shooting a scene, especially now in the digital age, your monitor shows you the images you're capturing in real time—or at least it should. Unfortunately, monitors have their limitations, from poor calibration to subpar color gamut, which is why knowing your way around a vectorscope is so important. In this video, Ted Sim of Aputure explains what a vectorscope is, how to use one, as well as when they're most useful.
Vectorscopes can look intimidating—like the lesson in math class for which you intentionally got Mono—but they're really not that difficult to wrap your head around. Essentially, a vectorscope is a visual representation of the chrominance signal (think about it as the color of the light hitting the sensor). They measure the data being captured by your camera's sensor, the values of which appear on a graph that looks like a color wheel.
Because these scopes measure color, it makes them great tools for a range of tasks that are directly related to color control and correction, like white/black balancing and keying. In fact, relying solely on your monitor can result in an unusable image, like if you white balanced using an uncalibrated monitor you could end up with subjects that look like, I don't kn—carrot people. Same goes for keying; if your monitor doesn't read the similarities between the green in your green screen and the green in your subjects shirt, you'll end up with a floating head—which is cool, but I guess, understandably, not always.