Photoshop has had the Lens Blur filter for a couple of versions now. You can use it to reduce the depth of field for a single shot. What if you want to extend the depth of field?
Photographers have long had the idea of taking a series of photos, each with different different focal points, to extend depth of field. There are a number of issues with this, such as changing focus for a lens also changes the subject magnification.
Photoshop CS4 includes a new feature called Auto-Blend Layers. With this new feature, digital photographers can take a stack of photographs of the same subject and extend the depth of field in the composite. Auto-Blend Layers automatically correct vignettes and distortions when stacking photos.
You can find the Auto-Blend Layers feature under the Edit menu in Photoshop CS4.