Camera Terminology for DSLR Lenses

Close up of a 72mm zoom camera lens

William Andrew / Getty Images 

The lens is arguably the most important component of a digital camera. Without a quality lens, your photos have no chance of being sharp and bright. Deciphering the differences among lenses is all but impossible unless you first know the terminology used to describe them.

Lenses have specific purposes, so know what you're trying to do before you shop. Are you after a particular effect? Are you shooting from far away? What are your subjects likely to be?

Useful Lens Terminology

The market offers an enormous variety of lenses and the terminology to match. Here are a few of the most common terms you'll see as you research your purchase.

Zoom

Nikon zoom lens
Nikon

Some photographers think of zoom as the magnification of an image, allowing the photographer to shoot a closeup photo without having to move closer to the subject. The actual definition for zoom, however, is the ability of a lens to shoot at multiple focal lengths. In other words, the zoom lens can shoot a wide-angle shot, a telephoto shot, or both. Not all lenses offer zoom capability.

Optical Zoom

Optical zoom is the ability to change the focal length of the lens using hardware, as opposed to digital zoom, which uses software algorithms (see below). It's considered "true" zoom: It changes magnification in a mechanical process that occurs before data reaches the imaging sensor, using the optical glass of the lens.

It produces far sharper images than does digital zoom and is a feature of fixed-lens cameras, not DSLRs.

Digital Zoom

Digital zoom uses software inside the camera to change the focal length by simply magnifying the image. Because digital zoom involves actually increasing the size of the pixels, digital zoom can affect image sharpness negatively. When buying a camera, don't look for or at digital zoom; most photographers can duplicate most aspects of digital zoom with post-production software. Pay attention to the optical zoom number instead.

Interchangeable Lenses

High-end DSLR and mirrorless cameras can use interchangeable lenses to provide different capabilities. With many interchangeable DSLR lenses and mirrorless camera lenses, image stabilization is built in, limiting camera shake and improving image quality.

Focal Length

The focal length is the distance from the center of the lens to the focal point (the image sensor in a digital camera). Most digital camera lenses express this number as a range, such as 25mm to 125mm. The focal length measurement more accurately measures the telephoto and wide-angle capabilities of a lens than the optical zoom measurement, which is simply a number signifying the difference between the wide-angle and telephoto measurement. The above 25mm-125mm example would have a 5X optical zoom measurement.

Other Terms: Seeing Your Subject

The following terms aren't strictly related to camera lenses, but they're useful to know nonetheless when you're shopping for cameras.

LCD

The liquid crystal display (LCD) on the back of a digital camera helps you frame a photo, as a viewfinder does. Keep in mind, though, that the LCD rarely frames 100% of the image that the camera will shoot. LCD coverage is sometimes 95% or higher, and the camera's specs typically list this percentage. It usually closely matches the view through the lens, but not exactly.

Optical Viewfinder

The optical viewfinder provides a non-enhanced, non-digital preview of the image the photographer is about to shoot. On low-end point and shoot cameras, the optical viewfinder is not tied to the lens optics; instead, it's usually above the lens, so it probably won't match the image the lens will shoot precisely. In contrast, high-end DSLR cameras tie the optical viewfinder to the lens optics, providing a perfect preview of the upcoming image.

Electronic Viewfinder (EVF)

The EVF in a digital camera is a tiny LCD that gives you a chance to frame the photo. The EVF is a digital representation of the image. In terms of mimicking the view through the lens of the final photo, the EVF closely matches the LCD's accuracy.