If you are relatively new to flash photography, you have likely heard of high-speed sync, but might not understand it. Here is a full explanation.
Have you ever tried using a flash and found that a large black strip ruined your image? This is a common question I see arise from photographers who are trying to figure out how to use artificial light for the first time. It’s an easy fix, as the problem has to do with the combination of your camera's shutter and the timing of the light you are trying to introduce into the scene. Your camera has a limit to the shutter speed that you can use to fully capture the light from your flash. This limit is unique to each camera, but usually, it is 1/200 of a second or so. If your flash has high-speed sync, it allows you to go above this speed by putting off multiple quick pulses as opposed to one single burst. All of this is explained in detail in the video above by Jay P. Morgan of The Slanted Lens.
So, why would you want to use high-speed sync and not just lower your shutter speed? There are multiple situations, but the primary reason has to do with combating ambient light. You could always raise your aperture in place of lowering your shutter speed to control the exposure of the background. However, this would sacrifice the background blur that you might prefer in the image. High-speed sync allows you to keep a higher aperture while using a fast shutter speed to limit the ambient light and still introduce flash into the scene. If you want to see a full explanation on how your camera’s shutter and a flash work together, take a look at the video above.