Another very important use of focal length is perspective and depth. This can only occur when you both zoom your lens and move your camera position. This was actually very well known in the days before zooms, but this part of the photographer's craft seems to have been lost with the extensive use of zooms. I do a class at BetterPhoto.com on getting impact from your photography and one of the lessons is about the use of focal length for impact. This is the hardest lesson for most students to understand because they are mostly used to zooming for composition and not using focal length for its effects on perspective and space, let alone impact.
This can be a valuable lesson to learn. Knowing how to change the look of a landscape with focal length can help when the light is not cooperating. No matter who you are as a photographer, no one has any control over the weather. Sometimes we get spectacular light, sometimes not. I was at Cape Cod last year for a couple of days before going up to Maine to visit my sister and her family and my parents. For any of you who know that area from last summer, it was a summer of endless rain!
But there was no way I was not going to photograph in that spectacular location. Cape Cod is a stunning place, even in the rain. But I am also uninterested in taking gray day snapshots just to show I was there. So I started playing with perspective and space by changing focal length (I was not out in the worst of the rain, though). That usually means getting in close with wide-angle lenses and backing up with telephotos, although when it is raining, scenes can lose a lot of color and tonality if you back up too much and have to shoot through all of that rain. On the other hand, getting in close with a wide-angle minimizes that problem and can give richer looks on such days. Getting in close with a wide-angle also means less blah sky in the composition, too.
Look at the photos here and notice how the scenes change in feel due to the use of different focal lengths. No, these are not all the "same" rose bushes in the wild rose shots -- it is pretty rare for me to simply move and change focal lengths on the exact scene and shoot both wide and tele. I am looking for the interesting scene as portrayed by my distance and focal length, not simply changing the look of a single scene. But you can see how perspective and space relationships change. The close shots with the roses up close were shot wide and have a deeper perspective and feeling of depth. The shot of the rose bush and dune without any sky was shot with a telephoto and has a flatter perspective and a shallower feeling of depth.
A good way to learn how to work with focal length beyond composition is to do this exercise -- go out with a camera and a zoom lens. Start taking a photo of a subject up close with your widest focal length. Then set the camera to its longest, most telephoto setting and back up until you can photograph that subject again. Then keep doing this by shooting a wide shot up close, then a telephoto shot from a distance. You will start to see the changes in perspective (how the background looks compared to the subject), space (what feelings of depth appear) and even depth of field (you won't always see this, but sometimes you do and it is a consequence of this exercise).
I will be leading a workshop in Cape Cod this September after Labor Day and all the crowds have gone. We will have a great time shooting the amazing range of landscapes there. You can see more at the Great American Photography Workshops website, www.gaphotoworks.com. Also, check out my new blog, www.natureandphotography.com.