What Is “Field of View” For A Lens?

What Is “Field of View” For A Lens?

by William Lulow

Each lens in your camera bag has special characteristics all its own. Long or telephoto lenses are usually large with long lens barrels. Short or wide angle lenses are usually much smaller. Here are a few different lenses. Notice what it is that makes them different:

The wide angle lens like the 20mm one above, is small with smaller curved lens elements. It is capable of showing an entire scene. Here is a picture made with the 20mm lens:

You can see how both sides of the street are shown as is the sky and the foreground. This particular lens is just a bit wider than what we might consider “normal” in terms of what it can include in the scene. Here is an image made with a slightly longer lens:

This image was made with my portrait lens, an 85mm f/1.8. Notice how the view is restricted. You can’t really see most of the location because the emphasis is on the person rather than the place. Note also, that the background is out of focus, another characteristic of telephoto lenses. Here is yet another image made with an even longer lens:

This image was made with my 135mm f/2 lens. Notice how part of the background is extremely soft and how that makes the part that is sharp really jump out at you.

Here is a chart that will give you relative fields-of-view of several focal length lenses:

In this chart, the 1.5 times the normal lens (normal lenses for 35mm, full-frame cameras are in the 50mm range) would be around 75mm and the 3.0 times the normal lens would be around 150mm. Just interpolating these measurements for cropped sensor cameras means that the “normal” lens would be around 80mm to obtain the results in the chart and the telephoto would be around 120mm. A wide angle lens on a cropped sensor camera would have to be around 15mm to 20mm and on a full-frame camera it would be roughly 32mm-35mm. This actually corresponds fairly well to what we used to use before digital cameras. My old 35mm camera kit included a 24mm, 35mm 50mm, 85mm and 200mm lens to cover most assignments I had at the time. I also had cameras that were larger format. For instance, my view cameras that shot 4×5″ film sheets had wide-angle lenses in the 90mm range. The “normal” lens for that size film was 135mm and the telephoto was more like 210mm. Also, back in those days, the focal length of many lenses was measured in inches, not millimeters. So the telephoto was an “8-inch lens,” and the wide-angle was a “3-inch lens.” The photographers I worked for in the early days would expect us to know this information, because they often asked for lenses in inches.

You can’t forget that when you use a longer lens, not only is the field of view less, but the depth-of-field is less as well. These days, photographers use this information to obtain images that  purposely have the backgrounds out of focus. It is sometimes referred to as “bokeh,” which means that the background is soft, but it makes the sharp parts of the image really stand out. Here is an example:

Notice how the foreground as well as the background is out of focus and how it concentrates the viewer’s eye to the main subject. Here is another example:

Now the effect of a particular lens also is dependent on the size of the film or sensor that is used to make the images. So, the smaller the sensor, the larger the image will be. In other words, a wide angle lens on a piece of 16mm film could be somewhere in the 10mm range whereas a wide angle lens for a larger, 4×5″ piece of film might be something in the 90mm range. So the effect of certain lenses depends on the material used to record the image. The photographer has to decide, given his camera and the size of its sensor (in the case of digital photography), how much of a scene needs to be shown for whatever the purpose of the photograph will be. If he or she is using a “cropped sensor” camera and wants to include roughly 130 degrees of the scene, they will need a lens in the 16mm-18mm range. The medium telephoto for this type of camera that would include roughly a 72 degree coverage would be in the 45mm range and the longer telephoto, which would include about 38 degree coverage of the scene might require something like a 100mm lens.

The take away here is that each lens (or lens setting on a zoom lens) has its own particular characteristics. If you are going to use a variable focus (zoom) lens you need to understand what each of the focal length settings means and what kind of an image will result. For instance, many people use the zoom lenses that come with their cameras and simply adjust them to get whatever size image they want without taking into account the characteristics of that size lens. If you are going to use your zoom lens on its telephoto setting, it will act like a telephoto lens; restricting the field-of-view, limiting the depth-of-field, adding more instability, etc. If you are aware of all of this then you can take steps to ensure that you get a good photograph. If you aren’t aware of lens characteristics, you will, most likely be disappointed in the results.

It is important to know these characteristics even if you use the new iPhone 13, which actually has three lenses you can use. If you intend to use the telephoto lens, you need to take steps to make sure that the camera is steadied (like on a tripod) and that you are aware of all the things a telephoto lens does!