How Aperture Priority (Av) mode works on the EOS Digital Rebel XSi

Article ID: ART104649 | Date published: 05/11/2015 | Date last updated: 09/29/2015


How Aperture Priority (Av) mode works on the EOS Digital Rebel XSi


To obtain a blurry background or to make everything near and far look sharp, set the Mode Dial to <f> (Aperture-priority AE) to adjust the depth of field (range of acceptable focus).

* <f> stands for Aperture value which is the size of the diaphragm hole inside the lens.

Set the Mode Dial to <Av>.

Set the desired aperture.

  • The higher the aperture, the sharper the picture will look with a wider depth of field.
  • Turning the <> dial to the right will set a higher f-number, and turning it to the left will set a lower f-number.

Take the picture.

  • Focus and press the shutter button completely. The picture will be taken with the selected aperture.

About the Aperture Display

The larger the f/number, the smaller the aperture opening will be. The apertures displayed will differ depending on the lens. If no lens is attached to the camera, "00" will be displayed for the aperture.

Shooting Tips

When using a high aperture, note that camera shake can occur in low light scenes.

  • A higher aperture will make the shutter speed slower. Under low light, the shutter speed can be as long as 30 sec. In such cases, increase the ISO speed and hold the camera steady or use a tripod.

The depth of field depends not only on the aperture, but also the lens and subject distance.

  • Since wide-angle lenses have a wide depth of field, you need not set a high aperture to obtain a sharp picture from the foreground to the background. On the other hand, a telephoto lens has a narrow depth of field.

And the closer the subject, the narrower the depth of field. A farther subject will have a wider depth of field.

Set the aperture so that the shutter speed display does not blink in the viewfinder.

  • If you press the shutter button halfway and change the aperture while the shutter speed is displayed, the shutter speed display will also change to maintain the same exposure (amount of light reaching the image sensor). If you exceed the adjustable shutter speed range, the shutter speed display will blink to indicate that the standard exposure cannot be obtained.

If the picture will be too dark, the 30" (30 sec.) shutter speed display will blink. If this happens, turn the <> dial to the left to set a lower aperture or increase the ISO speed.

If the picture will be too bright, the 4000 (1/4000 sec.) shutter speed display will blink. If this happens, turn the <> dial to the right to set a higher aperture or decrease the ISO speed.

Using the Built-in Flash

To obtain a correct flash exposure, the flash output will be set to match the set aperture (autoflash exposure). The shutter speed will set automatically between 30 sec. - 1/200 sec. to suit the scene's brightness.

In low light, the main subject is exposed with the automatic flash, and the background is exposed with a slow shutter speed set automatically. the subject and background look properly exposed (automatic slow-speed flash sync). If you are handholding the camera, keep it steady to prevent camera shake. Using a tripod is recommended. To prevent slow-speed sync, select the [ Custom Functions (C.Fn)] menu's [Flash sync. speed in Av mode] and set it to [1: 1/200sec. (fixed)].



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