Zoom lenses are the most common lenses by far. You can’t even by a camera kit without one. Many photographers today do not have the experience of working with a single focal length lens – I suspect that many folks don’t even know they exist. I remember years ago traditional photographers using the old line, “Yeah, I have a way of making my lens show more or less of the subject. It’s called using my feet!”
© Rob Sheppard
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DSLR Camera Lenses: How to Use Your Feet
There is something about “using your feet” that is not simply a joke. Focal length is more than simply a way to change your composition by zooming in on the subject or zooming out to show more of the environment. As you change your position, you change perspective, then the focal length allows you to see those effects. This is such an important part of lens usage that it used to be a critical part of any photographer’s learning years ago. But now with zoom lenses, this understanding of the relationship of distance, perspective and focal length is often ignored, which means really limiting your tools.
First, as you move close to a subject and zoom out (wider angle), you are strongly influencing perspective. Simply zooming from a fixed position does not affect perspective. Perspective can be an important factor in photographing a subject. Perspective is how distance appears in your photograph and is affected by space and relationships of objects from near to far. Perspective can be deep, shallow or anything in between.
As you get close with a wide-angle, perspective gets deeper. The subject gets larger in relation to the background, and the background gets smaller.