Bob, I have some experience with this. I use Photoshop CS5 to do the focus stacking, but there are other programs out there that can accomplish it.


Basically, you take 2 or more pictures, with each of them focused on a different part of the image. You load the images into the program, which "stack" the images one on top of each other. After you highlight all the images, you do blend of the images, and the program finds the areas that don't match and eliminates them.


In Photoshop, this is called a script.


It works best with static objects, like a landscape scene, where things are not moving (wind can cause blurring, depending on what is moving in the wind).


For me, most of my focused stacked processes are done with 2 images. I use the back AF button (disconnecting the shutter button from focusing). I set my camera to f/8, focus something close in the foreground (let's say, a rock or a bush), then move the camera to where I want the final image composition to be. I take the shot.


Without moving the camera, I hit the back AF button again, which will be on the background object (whatever that might be). It now refocuses on that object. I take the second shot.


These two images are put into Photoshop and a script is run on them, like described above.


The result is that Photoshop throws away all of the out of focus areas. The two images are then "flattened" and the resulting single image is in perfect focus from the foreground to the background.


It makes it possible to take a picture that has a very deep depth of field, without using high f/stops. I've found that the images are sharper than hyperfocal distant focusing, too.


Another great use is macro shots. You can get really close to, say, a flower, and take several manually focused images, stack them, and get a nicely focused flower from top to bottom.


Hope this helps.