The 7D has two fl ash synchronization modes: fi rst curtain and second curtain. The term curtain relates to the opening and closing of the shutter—the fi rst curtain refers to when the shutter is being opened, and the second curtain describes the point just before the shutter is closed (try to visualize a curtain on a stage opening and closing; the amount of time it’s opened is how long your shutter speed is).
The built-in fl ash on your camera can be synchronized to fi re during the fi rst curtain or the second curtain. This only applies to shutter speeds of 1/30 of a second or slower, since a faster shutter speed moves so quickly that the mode wouldn’t really matter. But for longer exposures, I fi nd that using the second curtain fl ash is usually the best option.
The basic idea behind the term flash synchronization ( flash sync for short) is that when you take a photograph using the flash, the camera needs to ensure that the shutter is fully open at the time that the flash goes off. This is not an issue if you are using a long shutter speed such as 1/15 of a second, but it becomes more critical for fast shutter speeds. To ensure that the flash and shutter are synchronized so that the flash is going off while the shutter is open, the 7D implements a top sync speed of 1/250 of a second. This means that when you are using the flash, your shutter speed cannot be any faster than 1/250. If you used a faster shutter speed, the shutter would actually start closing before the flash fired, causing a black area to appear in the frame where the light from the flash was blocked.
For example, imagine you are photographing a person running (let’s say from left to right) in a race. It’s somewhat dark outside, maybe at sunset, so you can get away with a slower shutter speed of 1/15 of a second, but you also want to use your fl ash to freeze the subject in place. If you take their photo in 1st Curtain Sync mode, the fl ash will fi re right away and the person will run across the frame during the rest of the exposure. Because you used a slower shutter speed, you will see blur in front of the runner, as the fl ash froze them in place at the beginning of the exposure. If you change your fl ash setting to 2nd Curtain Sync and take the same photograph, you’ll see some blur across the frame after you press the Shutter button, but the fl ash will fi re at the end of the exposure, making the blur appear behind the runner.
- Press the Menu button and use the Main dial to navigate to the fi rst camera setup menu tab, select Flash Control, and press Set.
- Use the Quick Control dial to select the Built-in Flash Function setting, and then press the Set button (A).
- Use the Quick Control dial to select Shutter Sync, press Set, and select 2nd curtain (B).
Now, when you are using a slow shutter speed (slower than 1/30 of a second), once you press the shutter you’ll notice a quick burst of light from the fl ash to measu