Have you ever noticed something interesting about cameras, though? What shape is the camera lens? What shape are the pictures they produce? That’s right! Round lenses produce rectangular pictures! What’s up with that?
This curiosity about cameras stems from the fact that the camera lens doesn’t produce the picture directly. Instead, the lens works in conjunction with another key part of the camera to produce the picture. In older cameras, that other key element is called film. In newer digital cameras, it’s known as the image sensor.
As light bounces off of an object you’re photographing, that light enters through the camera’s lens. The job of the lens is to bend that light and focus it onto the film or the image sensor.
Early camera makers quickly figured out that round lenses did the most efficient job of focusing light onto film. Could a lens be made into a different shape, such as a rectangle? Of course, lenses could be made in any shape, but camera pioneers figured out early on that round lenses created the best images on film.
So what about the film then? If the camera lens was round, why make a rectangular film? Early camera makers decided upon rectangular film for a couple of reasons.
One of the reasons makes common sense if you think about it. Think about all of the pictures you see, whether they’re photographs, paintings, or posters. What shape are they? The vast majority of them are rectangular or square. Why is that?
If you think about displaying pictures, we usually display them on walls, which are what shape? You got it: rectangular or square. When it comes to framing and displaying pictures, it’s much easier to use a rectangular or square shape, because the frames are easier to create and they’re easier to display on walls of a similar shape.
So it’s only natural that camera makers would’ve thought about making films that would create rectangular photographs. Practically, though, there was another reason. If you’ve ever seen a film from an older camera, you know that it comes in a long strip that unwinds as pictures are taken. It’s simply more efficient to use rectangular film in a camera rather than a series of ovals or some other shape.
Likewise, today’s modern image sensors in digital cameras have retained a rectangular shape. In addition to maintaining the traditional shape of the film, using a rectangular sensor also leads to better pictures.
A round camera lens does produce a round image inside the camera. However, the outer edges of the round image will have more distortions, sometimes called aberrations, than the parts of the image closer to the center. This is because light must be bent more to reach the outer edges of the circular image.
To correct for these aberrations and end up with the best image possible, the rectangular sensor crops out the outer edges of the circular image from the lens. In other words, it only keeps the best part of the image from the lens. This gives you better photographs than you would get if you kept the entire circular image from the lens.