Your camera may boast “8x zoom”, but most DSLRs do not advertise values like these. So how do they compare? The answer is more complex than you may think.
That “8x” value that doesn’t necessarily mean objects in the photo will look 8 times bigger than they do with your eyes. It just means things will be 8 times bigger than its most zoomed-out position—but two cameras in their most zoomed-out positions will not look the same size.
Every lens affects your image in a different way. A wide angle lens warps the perspective in the image so it shows more than you could see with your naked eye. A telephoto lens does the opposite, zooming in like a telescope to distant objects. These things are separate from the actual “zoom” function on your camera, so one 8x zoom lens may not make objects as large as another 8x zoom lens.
So how do we calculate how much bigger an object appears in a photo compared to your eyes, where you’re currently standing? To find that out, you need to know the focal length and field of view of the lens you’re using.
Focal Length and Field of View
In photography, the focal length of a lens is the distance between a the camera’s sensor and the internal components of the lens itself. This focal length determines how close objects look to your camera and what part of the scene actually fits within the picture—otherwise known as your field of view. A massive, telescope-like lens with a 1000mm focal length will make objects look very close. Lenses with smaller focal lengths will make objects appear farther away.
Many lenses can “zoom” to different focal lengths. For example, an 18-135mm lens will let you zoom from an 18mm focal length to a 135mm focal length.
Here’s an example. I shot the following two images with my Canon 650D and an 18-135mm lens.
The first photo was taken at the shortest focal length: 18mm. It’s a pretty wide field of view.
The next photo was taken in the exact same place half a second later. The only difference is that I’ve zoomed in to use the lens’ longest focal length, 135mm.
As you can see, the field of view is a lot narrower in the second photo than the first, because we’ve zoomed in on the mountains.
Here’s the catch, though. Different lenses, at their shortest focal length, will show things differently. Remember that 1000mm telescope lens? Even if you don’t zoom in with it, you’re still seeing things much closer than a camera with an 18-135mm lens. So focal length alone isn’t…