This is my first real post on photography. I'll try not to bore the crap out of you. (Oh, the pressure, the pressure.) Before I get rolling, though, I need to give you a splash of photography 101.
The two most basic functions of the camera are shutter speed and aperture (i.e., how big the lens opening is). Both control how much light gets into the camera, so in a way, they work against each other. For example, the faster the shutter speed, the larger the aperture must be to let in enough light. The slower the shutter speed, the smaller the aperture must be to keep too much light out.
The biggest factor in shutter speed is motion. If you are taking a picture of a racecar, you need a fast shutter speed to avoid blur. On the other hand, you might want a slow shutter speed to paint the movement of a waterfall. The thing to keep in mind, however, is that most people cannot hold a camera still below a shutter speed of 1/60 of a second. Therefore, unless you have a tripod, you can't realistically go much slower than that.
So, what about aperture? What the heck does that do? Well, the most important effect of aperture is depth of field, which in English means how much of the shot will appear to be in focus. According to some impressive formulas with funky mathematic symbols, the physics of light causes more of the picture to be focused when the lens opening is very small. Let me demonstrate.
These three pictures were taken with increasingly smaller apertures.
Here, only the middle blossom appears to be in focus and the background is very blurred. Large aperture.
With a smaller aperture, the depth of focus deepens and the background comes more into focus (actually, not a desirable thing if the background is distracting).
With even smaller of an aperture, most of the branch comes into focus, but the background is kind of busy.
As you can see, in close (macro) photography, the depth of field is very small. Who wants a gorgeous close-up of a flower where only a few specks of pollen are clear? Blech! So what do you do? Well, you could decrease the aperture like I did above to widen the field.
Well, not so fast. Unless your subject is very brightly lit, by the time you make the aperture very small, you will have to make the shutter speed too slow to handhold the camera. Add in some wind or entirely too much coffee, and you're screwed. Now what?
Well, you could add a flash to solve the light problem. However, the artful use of flash is whole other can of worms. I hate nothing more than a shot with heavy and harsh flash. It looks like the subject is a millisecond away from getting vaporized by an intercontinental ballistic missile.
Here is where stacking comes in. By keeping the aperture large (wide), you can isolate the subject from the background while creating an impossibly large depth of field. Using a tripod (sorry, you're stuck with one now), you inch the focus forward through the subject bit by bit in a series of photos. A stacking program then creates a composite image using only the clear portions.
Here is the process in action.
Note how the first photo is clear on the left, but blurry on the right. By the time you reach the 6th photo, the right is the clear side and the left blurry.
Now comes the fun part. Take these 6 otherwise pitiful pictures, and stack them with a program far smarter than I am. Voilà! You've done the impossible.
Okay, now you have some crazy mad tools. Go get stacked.