Just What IS Normal, Anyway?

So, if the focal length of the lens doesn’t determine the perspective, but your position does, what focal length should you use? The same as your eyes? What is the focal length of our eyes? What really constitutes a “normal” focal length?

To find this out, I mounted a standard zoom lens to my APS-C digital camera, and did a little double-eye viewing. Indeed, it doesn’t matter what I set the focal length to, the perspective does not change. That is, the proportion of the background and the foreground remain the same. But of course what does change is the overall scale of things. So, I zoom back and forth concentrating both eyes on the scene before me, until the two line up perfectly. It was pretty easy to tell once I got it right, because my eyes now seemed perfectly relaxed and were no longer competing with one another. They were in a sort of harmony. And my lens read about 55mm. Factor in the 96% coverage of the finder, and it becomes a little over 57mm.

So, in order to take a photo that looks exactly like what I see before me, I need to use a 57mm lens. I also tested this will a full-frame camera, and the adjusted focal length is approximately 76mm.

So does this mean that on an APS-C camera a 57mm lens is normal, and on a full frame camera a 76mm lens is normal?

No. In fact, it doesn’t mean much of anything.

Our eyes see very differently than a camera. Our peripheral vision spans nearly 180°, and yet we see clearly only the small portion of the image we look at directly. When we look at a scene, we can both take it all in and scan it for individual details as we deem necessary. Sort of the equivalent of using a longer lens and making a composite image image of multiple frames, which is actually the whole premise behind the newer digital cameras that create panoramic images by “stitching” together individual ones captured during panning.

But when we make a photograph, we need to control what the viewer sees, which we do by “containing” it within the frame. It doesn’t matter whether we do this with lenses of varying focal lengths, or by cropping; the effect is the same.

As sensor resolution increases, the need for longer lenses decreases. Digital zooming is highly criticized, and yet if the native resolution of the sensor is high enough it no longer becomes an issue. cropping or zooming; it’s all the same.

So when choosing the focal length of a lens, keep these two facts in mind:

Moving in closer creates a sense of depth in your images, not using a wide-angle lens. The lens just allows you to fit more of the image before you into the frame.

Moving further away makes the image appear flatter and more shallow, not using a telephoto lens. The lens just allows you to fill the frame with your subject from a distance.