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Controlling depth of field

When a lens is focused on a subject, there is a certain range behind and in front of the subject that remains sharp, as mentioned in the part "the aperture". This range is called "Depth Of Field" or DOF. The photos show how depth of field varies with the aperture selected.

  1. Large apertures (e.g., f/1.7) yield a shallow field of sharp focus, rendering the background and foreground unsharp
  2. Small apertures (e.g., f/22) yield greater depth of field with more of the scene in focus

At a given aperture and focal length, depth of field also varies with subject distance: When the lens is focused on a close subject, depth of field is less; when focused on a distant subject, depth of field is greater. Focal length does also affect DOF; a wide angle lens will give a large DOF, while a tele lens gives a shallow DOF.

DOF preview lever

The preview lever can be used in all exposure modes to close down and lock the lens' aperture. This enables you to determine whether depth of field is sufficient. The lever is hinged and folds up against the handgrip when not in use. To use:

  1. Focus on the main subject.
  2. In A or M mode, set the desired aperture. In P or S mode, meter in the usual way.
  3. With film advanced, press the preview lever partly down and release it. Lens aperture will now be locked at the setting displayed in the data panel. "F" blinks in the data panel while the preview lever is used.
  4. Look through the viewfinder to determine DOF. When the lens is closed down, autofocusing does not operate and it is not possible to adjust the aperture setting. Also, the viewfinder image may appear dark, but this has no effect on exposure.
  5. To cancel the preview operation, press the preview lever all the way down and release it. The aperture setting can now be adjusted by using the up/down controls as usual. The DOF preview is also cancelled if the shutter is released with the lens stopped down.

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