How Telephoto and Wide-Angle Lenses Work

Focal Length in Film and Digital Cameras

One of the first questions people new to photography ask is, "What is focal length?" The simple answer of course, is that this is what the camera sees, measured in millimeters. Explained further, focal length determines how much of a scene the lens can capture and how far or close, and how large or small subjects can appear.

Determining how focal length affects distance is quite simple; on the rim of the lens is a measurement in millimeters, (17 - 55mm, 70 - 300mm, etc.). This measurement gives an idea as to how close or far away the subject will appear through the lens. If there is a large number, ie 300mm, an object will look very large and very close. If on the other hand, you have a lens that is shorter or has a smaller number, ie 17, the object will seem smaller and further away.

Telephoto and Wide-Angle Lenses

In the days of film cameras and for purists still using them, the "Focal Length" was based off the size of the film. For example, the standard was 35mm film so a 35mm lens would be considered "standard". With the release of digital cameras that no longer use film, we have digital sensors. These sensors are often smaller than 35 mm and as a result using a 50mm gives you a standard "what you see is what you get".

This can get very confusing trying to calculate out the correct lens to sensor ratio, so in short, unless the camera says or is advertised as "full frame" odds are pretty good it is a smaller digital sensor and 50mm will be your standard "what you see is what you get".

We've established that for most people a 50 mm lens is going to be standard. Anything smaller than our standard (50 mm) is considered a "wide angle" lens. In other words when you look through the lens your subject will be further away and you will see more of the surrounding area. Anything that is larger than the standard (50 mm) is considered a Telephoto lens. When you use one of these, your subject will appear closer and you will see less of the surrounding area.