What does "single focal length" mean on a lens?
Asked 12/22/2011
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I saw the Nikon AF-S DX Nikkor 35mm f/1.8G described as a "single focal length" lens. What does that mean, and how does it compare with a zoom lens? What are the main disadvantages of a single focal length lens versus a multi-focal-length lens?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
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A single focal length, or "prime", lens has a fixed focal length, as opposed to a zoom lens which has a range of focal lengths. So a prime lens will be a 35mm lens, or a 50mm lens, or a 200mm lens. A zoom lens will cover a range, say 70-200mm.
Prime lenses are generally sharper, less expensive, lighter weight and have larger maximum apertures, which is useful in low light. This is because these lenses can have a much simpler design, since the lens only has to work at the one focal length, and can be optimised for it.
Zoom lenses have the advantage that you can use one lens and cover a range of focal lengths, rather than owning several prime lenses and having to swap lenses all the time. You can also zoom in or out to compose a shot. With a prime lens you'd have to move closer to, or farther away from, the subject ("zoom with your feet"), or switch lenses.
Originally by user4191. Source · Licensed CC BY-SA 4.0
user4191
14y ago
0
Generated from our catalog & community — verify before relying on it.
A "single focal length" lens is a fixed-focal-length lens, commonly called a prime lens. It does not zoom: a 35mm prime always stays 35mm, while a zoom lens covers a range such as 18-55mm or 70-200mm.
Compared with zooms, prime lenses are often:
- sharper
- lighter and simpler in design
- less expensive for similar image quality
- able to offer wider maximum apertures, which helps in low light and with shallow depth of field
The main disadvantage is flexibility. With a prime, you cannot zoom in or out to change framing, so you usually need to move closer or farther from the subject. In situations where you cannot move easily, this can be limiting. You may also need to carry and swap multiple prime lenses to cover different angles of view that one zoom could handle.
So the trade-off is usually convenience and versatility (zoom) versus simplicity, image quality, and often a larger aperture (prime).
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