There are 2 kinds of photographers:

  1. The aperture priority photographers
  2. The shutter priority photographers

The manual photographers do not count, they are so rare that they are lobbying for being listed under the Endangered Species Act.

Like the vast majority of the photographers, I’m an aperture priority photographer. To my shock and dismay, when I first hooked my flash to my Canon 7D, the flash worked but the shutter staid open “forever” seconds…

I didn’t know that it’s the Canon default in Av. In Av, Canon sets the fill-in flash. The flash works to balance the subject and the background.

The answer: switch to Tv, the shutter priority

Or disable the fill-in flash by restricting the shutter speed, and that’s where the C. Fn I - 7 — Flash Sync Speed in Av Mode comes in:

  • 0 — the default setting sets any shutter speed to be set between 1/250sec and 30sec, the speed will be determined by the background. It’s a 13 f/stops range.
  • 1 — sets the shutter speeds from 1/250sec to 1/60sec. It’s a 2 f/stops ranges.
  • 2 — sets the shutter speed to 1/250sec fixed: no variation. It’s a 0 f/stop range!