There are lots of unfortunate error codes that digital SLRs can produce. Canon users may be familiar with ERR 01, which means the lens isn’t correctly mounted on the body and the two aren’t communicating effectively. Nikon shooters may have seen the “CHA/CHR” error message, which tells them there’s a problem with their memory card. But what if your camera reports an error with an “L” that appears on the top-of-camera LCD panel every time you try to change your aperture?
The “L” that shows up in this scenario sure looks like an error message, but in fact it’s not. And because you can’t change your aperture either it seems especially like there’s a problem. But in fact, that disappearing “L” is simply your camera’s way of reminding you that the scroll wheel on the back of the camera—the big round dial that’s officially called the Quick Control Dial—is in the locked position.
By default, Canon DSLRs assign the aperture control to this back-of-camera dial, while shutter speed controls are relegated to the Main Dial just behind the shutter release button. These controls are customizable, so there’s the possibility that you could be seeing your own “L” message when you try other camera controls. Whenever you see it, however, look to the Quick Control Dial to verify that it’s locked. If it is, simply slide to unlock it and voila, your aperture or other camera controls are again operating as usual.
Not all uses of the Lock mechanism are inadvertent. You may sometimes want to lock the controls if you have dialed in the exact aperture you’d like to use so that you don’t accidentally change it. The lock can be immensely helpful in situations where an errant exposure change could throw off the entire shoot. Don’t hesitate to use it intentionally when the time is right. Until then, if you find that your camera mysteriously won’t let you adjust the aperture and it’s displaying a vague “L” message atop the LCD, rest assured that your camera isn’t broken—you just need to unlock the dial on the back of the body.