Camera Lens Knowledge Quiz — Test Your Understanding

A prime lens has one focal length and cannot zoom, so you change framing by moving. Primes are often smaller, sharper and have wider maximum apertures than zooms covering the same focal length. The term has nothing to do with who makes the lens or what it costs.

On a full-frame camera, a lens around 50mm gives an angle of view and perspective close to how the eye sees a scene, so it is called normal. The frame's diagonal is about 43mm, and lenses from roughly 40 to 58mm count as normal. 35mm is mildly wide and 85mm is a short telephoto.

A lower f-number means a larger opening, which lets in more light. That allows faster shutter speeds or lower ISO in dim conditions and gives a shallower depth of field for blurred backgrounds. Angle of view depends on focal length, not aperture.

Lens compression is the flattened look of telephoto shots, where distant objects seem stacked close behind nearer ones. It really comes from standing far from the scene, which makes near and far objects appear closer in size; a long lens is what lets you fill the frame from that distance. Nothing in the lens is squeezed.

Wide-angle focal lengths between 14 and 35mm include a broad angle of view that captures expansive skies, dramatic foreground elements, and the full sweep of a landscape in a single frame, which narrower focal lengths cannot accommodate.

Bokeh, from a Japanese word for blur, describes how the out-of-focus parts of an image look, especially points of light that turn into soft discs. It depends on the lens design, the shape of the aperture and how far the background sits behind the focus point. It is about the quality of the blur, not just the amount.

A macro lens focuses close enough to project the subject onto the sensor at life size, a 1:1 ratio, or near it. That lets small subjects such as insects, flowers and textures fill the frame in fine detail. Ordinary lenses usually stop at about a quarter of life size or less.

Stabilization moves lens elements or the sensor to counter small movements of the camera, so handheld shots stay sharp at slower shutter speeds, often by several stops. It cannot stop a moving subject from blurring; only a faster shutter speed does that.

Ultra-wide lenses, and fisheyes most of all, cover a very wide angle, and straight lines near the frame edges bow outward. That is barrel distortion. Fisheyes keep it on purpose to fit a view of up to 180 degrees, while long telephotos tend toward mild pincushion distortion instead.

Glass bends each wavelength of light by a slightly different amount, so red, green and blue may not focus at the same point. The result is colored fringes, often purple or green, along high-contrast edges. Special low-dispersion glass and lens correction in editing reduce it. It is a lens effect, not a sensor fault.