Lens names and specifications are full of shorthand, but each term points to something practical: how wide the view is, how much light gets in, and how the lens attaches to your camera. This glossary defines the common words in plain language, with short examples.
Reading the Numbers
Focal length is given in millimeters and sets the angle of view. Lower numbers show more of the scene, and higher numbers magnify distant subjects.
- 14 to 24 mm: ultra wide, often used for interiors and landscapes.
- 35 to 50 mm: close to natural everyday perspective.
- 85 to 135 mm: popular for portraits.
- 200 mm and above: telephoto for sports and wildlife.
Maximum aperture is the widest opening, such as f/1.8. A zoom may list two values, like f/3.5-5.6, because the opening narrows as you zoom in.
Lens Types
A prime lens has one fixed focal length. A zoom lens covers a range, so you can change the view without moving. A macro lens focuses very close for small subjects like flowers. A fisheye lens gives an extreme, curved wide view. A teleconverter is an add-on that increases the reach of a lens, usually with some loss of light.
Build and Handling Terms
- Mount: the connection between lens and camera body. It must match.
- Image stabilization: a system that counters small hand movements, helping at slower shutter speeds.
- Autofocus motor: the part that moves focus elements, which affects speed and noise.
- Weather sealing: gaskets that resist dust and moisture, though the maker’s guide shows the exact limits.
- Filter thread: the screw size at the front that holds filters.
Image Quality Terms
Sharpness is how crisp fine detail looks. Vignetting is darkening toward the corners, often strongest at wide apertures. Distortion bends straight lines, as in barrel or pincushion shapes. Chromatic aberration shows as color fringes along high contrast edges. Flare is stray light that creates haze or bright shapes, and coatings are thin layers on the glass that reduce it.
Sensor Coverage Table
| Term | Meaning |
|---|---|
| Full frame | Lens covers a sensor about 36 by 24 mm |
| Crop sensor | Smaller sensor, narrower view with the same lens |
| Crop factor | Number used to compare views between sensor sizes |
FAQ
What does a lens hood do?
A hood blocks stray light from the sides, which reduces flare and protects the front glass from small bumps.
Why do some lenses have two aperture numbers?
Variable aperture zooms let in less light at the long end. The first number applies at the widest view and the second at the longest.
The Short Version
Focal length sets the view, aperture sets the light, and the mount decides what fits your camera. Learn those three first, and the rest of the lens vocabulary falls into place.
