Getting Really Deep
Ansel Adams and others of his generation popularized a style of landscape photography noted for extreme depths of field. If you've tried emulating this look, it isn't always easy. Here are a few ways to achieve it, including some Ansel never imagined.
The inherent relationship between aperture and depth-of-field provides the most straightforward means of controlling how far into an image you can see. Shoot at f/2.8 or similarly wide aperture, and only a narrow range of distances will render in focus. Stop the lens down to f/22, and the depth-of-field will substantially increase. Most aspiring photographers learn this early and aren't afraid to use it.
But all too often, I see photographers fall prey to the temptation of reflexively cranking the aperture as tiny as their lens permits. If it goes to f/22, they shoot at f/22. If they're fortunate enough to have a lens that reaches f/32, they reach for it without a second thought. They want the most depth-of-field possible. But beyond a certain point, image quality will degrade through diffraction. Light bends somewhat as it passes near an edge. This phenomenon has a negligible impact at moderate apertures, but with a small enough hole, there's an edge close by everywhere. This problem can be especially significant if you shoot with a smaller format, such as Nikon's DX sensor. When shooting, use the viewfinder or LCD back to select the aperture you need. Don't just go for the max.
Focus distance provides a less obvious means of controlling depth, but one worth considering in certain situations. If you take a photograph of Mt. Rainer, it's easy to achieve miles of focus when everything in the frame is sufficiently far away. But as soon as you try to include a foreground wildflower just inches from the lens, you will have a dilemma. You can focus on the flower and let the mountain go soft, or you can get a sharp background with a blurry flower. But if you back up enough from that flower, you will get both into focus. It isn't the absolute distance between foreground and background that creates the problem. It's the relative distance from the lens between the two. Sometimes, all it takes is a change of shooting position to get everything you want in focus.
Unfortunately, this won't work for everything. Besides focus, perspective also varies based on foreground distance. As you back up, that foreground flower will shrink in size more rapidly than the mountain behind it. It is often incorrectly stated that wide-angle lenses distort perspective. But in fact, perspective is determined by relative distance. It's just that you have to get quite close to something with a wide-angle lens to have it fill a reasonable portion of the frame. Back up far enough, and you will lose the impact of having that in-your-face foreground. As with many things, there's a tradeoff between perspective versus the range of focus distance.
As a third option, there's a type of lens known as a tilt/shift designed to make the most of your available depth of field. With a standard lens, the depth-of-field extends forward in the direction the lens is pointing. As its name implies, a tilt/shift lens lets you tilt that range of focus down at an angle to encompass both foreground and background better. Be forewarned that such lenses don't come cheap, nor are they that easy to use without practice. But they can let you get an image not otherwise possible in a single shot. Large format view cameras like the ones Ansel Adams shot with work on this principle. I have several, but honestly rarely use them these days.
And so, we come to the type of solution Ansel Adams didn't have available in his day. As much as he was famous for leveraging the power of the darkroom to create better images, there are limits to what is possible with film. Seemingly, the skies the limit with digital. With enough time or the right tools, it's possible to stack multiple captures into a single composite image to achieve depth-of-field far beyond the laws of optics permit with a single press of the shutter. The future of extreme depth-of-field is focus stacking.
The idea of focus stacking is simple. Lock your camera on a tripod and then shoot a series of frames varying only the focus distance. Aperture, shutter speed, and all other settings should be kept consistent. To avoid surprises, shoot on fully manual focus and manual exposure if you can. After the fact, you can use software to merge those frames to render an image that could never have been shot traditionally. When this first became possible, it required expensive, specialized software, but today, Photoshop, Lightroom, and many other general digital editing applications can do it. If you're interested in exploring this option, it's worth trying different programs to see which you like best.
Focus stacking works best when the wind isn't blowing, so everything stays put between frames. But if you plan things right, you can minimize the problem. Any motion will be more apparent near the camera, where objects are more prominent. The farther something is from the camera, the smaller it will appear, and the fewer problems it will present. If you can plan your photo such that a single frame covers the needed depth-of-field of your principal subject, you can use it for the foreground and let focus stacking do the best it can with the background. What hasn't changed since Ansel Adams' day is that the best results generally take a bit of planning.
Regardless of how you achieve it, images with extreme depth-of-field can be satisfying both to create and to see. It's fun to get really deep.