Sony DSLR-A100 - Manual (Page 70)

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Depth-of-field preview
The viewfinder shows an image captured with the widest aperture. The change in aperture
affects the sharpness of the subject image, creating a discrepancy between the sharpness seen
in the viewfinder and in the actual picture. The preview function enables you to see the image
with the aperture used in the actual shooting, allowing you to check the approximate sharpness
of the subject image before the actual shooting.
Press the depth-of-field preview button after the subject is in focus.
While the button is held down, the aperture is narrowed to match the aperture value displayed in the
viewfinder.
• About aperture and blurred images, t aperture priority mode (page 34)
• The image in the viewfinder will be darker because the aperture is narrowed (aperture value is greater.)
• The aperture value can be changed during preview.
• When the focus is not fixed and the preview button is pressed, you cannot take a picture. To take a picture,
press the depth-of-field preview button with z lit in the viewfinder.
• With a lens equipped with a focus hold button, you can set the camera to perform the preview function
using the focus hold button (page 93).
Depth-of-field preview
button