Canon EOS Rebel T6i / 750D For Dummies
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Aperture and shutter speed give you refined control over your Canon camera pictures. Which Creative Zone exposure mode on the Canon EOS Rebel T8i/850D you choose determines your level of control over aperture and shutter speed and also determines the method you use to adjust those settings. Here’s the scoop on adjusting aperture and shutter speed on your Canon Rebel.
  • P: You can choose from different combinations of aperture and shutter speed, but have no direct control over either. To view the camera’s recommended combination, compose your shot and then press the shutter button halfway. To select a different combination of the two settings, rotate the Main dial.
  • Tv: You control shutter speed; adjust that setting by rotating the Main dial. After selecting the shutter speed, frame your shot and press the shutter button halfway to initiate autoexposure metering. The displays then show the aperture setting that the camera selected to expose the picture at your chosen shutter speed and the current ISO.
  • Av: The opposite of Tv mode, Av mode enables you to set the f-stop while the camera selects the shutter speed. Rotate the Main dial to set the aperture setting you want to use. Then frame your subject and press the shutter button halfway. The camera then displays the shutter speed it selected.

Even though you’re in aperture-priority mode and so concentrating on the f-stop, always check the shutter speed that the camera selected for you. If the shutter speed drops so low that handholding the camera or capturing a moving subject won’t be possible, you can either open the aperture (choose a lower f-stop number) or dial in a higher ISO setting, which will enable the camera to select a faster shutter speed at your preferred f-stop.

  • M (manual exposure): You set both aperture and shutter speed. Use these techniques:
    • Adjust shutter speed. Rotate the Main dial.In M mode, you have access to Bulb mode, which keeps the shutter open as long as you keep the shutter button pressed fully down. To get to the Bulb setting, go one step past the slowest possible normal shutter speed (30 seconds).
    • Adjust aperture. Rotate the Quick Control dial.

Be sure to use the Main dial to lock in your setting when working in the P, Tv, or Av modes. In those modes, rotating the Quick Control dial applies an exposure adjustment called Exposure Compensation.

In the Av, Tv, and M exposure modes, you also can adjust the exposure settings on your Canon camera as follows:
  • For viewfinder photography, use Quick Control mode. After pressing the Q button or tapping the Q touchscreen symbol, highlight the setting you want to change and then rotate the Main dial. The Quick Control method doesn’t work in Live View mode, unfortunately.
  • In Live View mode, use the touchscreen. Just tap the setting on the touchscreen to display a screen that offers the available values for that setting.
A few more words of wisdom related to aperture and shutter speed for the Canon EOS Rebel T8i/80D:
  • Check the meter for guidance in M exposure mode. Of course, you don’t have to follow the camera’s guidance—you can take the picture using any settings you like, even if the meter indicates that the image will be under‐ or overexposed.
  • In Live View mode, keep an eye on the Exp Sim symbol. The live monitor preview updates as you adjust exposure settings to show you the change in image brightness. But if the camera can’t display an accurate preview, the Exp Sim symbol in the lower-right corner of the screen appears dimmed. (This happens, for example, when you use flash.)
  • In P, Tv, and Av mode, the shutter speed or f‐stop value blinks if the camera isn’t able to select settings that produce a good exposure. If the problem is too little light, try raising the ISO or adding flash to solve the problem. If there’s too much light, lower the ISO value or attach an ND (neutral density) filter, which is sort of like sunglasses for your lens—it simply cuts the light entering the lens. (The neutral part just means that the filter doesn’t affect image colors, just brightness.)
  • Say “nay” to Safety Shift. If you dig into the Custom Functions warehouse found on Setup Menu 5, you find Custom Function 4, Safety Shift. This feature, when enabled, gives the Canon camera permission to fiddle with your chosen f-stop in Av mode or shutter speed in Tv mode if it thinks that you’re headed for an exposure disaster. The option is disabled by default, and that’s how you should probably leave it. The recommendation is based on a couple of assumptions. First, if you’re using Av or Tv mode, it’s because you want to be the one controlling the f-stop or shutter speed. If you wanted the camera to stick its nose into your business, you’d shoot in Scene Intelligent Auto or P mode.

Second, the camera does alert you to impending doom by blinking the f-stop or shutter speed value in the displays, as mentioned earlier. If you pay attention to those signals, you can decide how you want to solve the problem. You—not the camera. Finally, if Auto ISO is enabled, the camera is already free to adjust ISO as an exposure assist—although, granted, it may not be able to choose an ISO low enough to avoid overexposure or high enough to prevent underexposure.

On some higher-end Canon models, you can give the camera a couple of options for how it responds when it senses exposure peril in Av or Tv modes. But on the T8i/850D, you either can say “yay” or “nay,” which means that you don’t really know how your settings will be adjusted. So for most, Safety Shift is a no-brainer: Keep it turned off.

  • You can adjust the exposure results that you get in the P, Tv, and Av modes. When you use these semi-automatic exposure modes, the settings that the camera selects are based on what it thinks is the proper exposure. If you don’t agree with your Canon camera, you have two options. Option one is to switch to manual exposure (M) mode and simply dial in the aperture and shutter speed that deliver the exposure you want. Or if you want to stay in P, Tv, or Av mode, your other option is to try using exposure compensation.
Want to learn more? Check out our Canon EOS Rebel T8i/850D Cheat Sheet.

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