Thanks, Salty. My dad lives in Davison (I was born in Flint and grew up in Clio), and I've already warned him that I was going to visit soon, but that he'd basically be serving as a hotel so I can meet you folks and fill up some digital cards.
Image stacking is a means of artificially increasing the depth of field so that more of the subject is in focus than is possible with a single shot. For example, in that first shot, if I used an aperture of f/25 to get maximum depth of field (the amount of the coral piece that is in focus front to back), I would have to make a decision about what part I wanted to go out of focus, because f/25, as close as I am to the coral, will not render the entire piece of coral in focus. (f/25 is the smallest aperture I can comfortably use with my 180 macro lens.) Typically I would choose to let the back portion go out of focus.
By stacking images, I can take a series of shots (16 in this case), starting by focusing at the front of the coral and moving the point at which I focus deeper into the scene with each successive shot. This technique also allows me to use a wider aperture (f/13 in this case), which keeps the area behind the coral blurred.
Once the images have been shot, you use software (I use Helicon Focus) to stack those images, eliminate what's out of focus, and keep what's in focus from each image.
Each image has to be exactly the same, i.e., you can't change the exposure, angle of view, or camera positioning. The only thing you change with each image is the point in the scene at which you focus. You also have to make sure you overlap your DOF with each shot so you don't have small lines of out of focus data.
It sounds much more complicated than it is, but I'll also say it has taken a little practice to get acceptable images. The quality isn't where I want it, but it's getting better.
Gary
