The lens focuses light and produces a sharp image on the sensor. There are prime lenses with high quality and zoom lenses for more flexibility. Important features include focal length, aperture (f-number), and magnification ratio. Different types of lenses are suitable for various uses, such as macro, tilt-shift, or mirror lenses. A 50mm lens with f/1.8 is ideal for beginners.
Category: Photography Basics > 2. Camera Technology & Construction Article ID: 2.5 Created: May 2026
Key Points in Brief
- The lens is the "eye of the camera": it focuses light and creates a sharp image of the subject on the sensor
- The most important difference between lenses: Prime lens (fixed focal length, high quality) vs. Zoom lens (variable focal length, more flexibility)
- Important lens specifications: Focal length (mm), Aperture (f-number), and Magnification ratio
Explanation
How Does a Lens Work?
A lens consists of several combined lens elements that together act like a converging lens. Incoming light is focused and projected onto the sensor (or film) as a sharp, reduced image of the subject. Multiple lenses made from different glass materials are combined to correct optical aberrations and focus light of various wavelengths onto the same point.
The image initially appears upside down – the camera automatically rotates it correctly.
Prime Lens vs. Zoom Lens
Prime Lens (Fixed-Focus Lens)
- Fixed, unchangeable focal length (e.g., 35 mm, 50 mm, 85 mm)
- Usually higher aperture (smaller f-number) and better image quality
- No moving lens groups → simpler construction, fewer optical errors
- Ideal for: portrait, street, and documentary photography
- Disadvantage: No zoom – the photographer must move physically
Zoom Lens (Variable Lens)
- Variable focal length by shifting lens groups (e.g., 24–70 mm)
- More flexibility without changing lenses
- Usually somewhat lower aperture than comparable prime lenses
- Ideal for: travel, event, and all-around photography
- Disadvantage: Compromise in image quality and aperture compared to prime lenses
Important Lens Types by Focal Length
| Type | Focal Length (Full Frame) | Typical Use |
|---|---|---|
| Super Wide-Angle | < 24 mm | Architecture, landscape, interiors |
| Wide-Angle | 24–35 mm | Street, documentary, travel |
| Standard Lens | 50 mm | All-around, similar to human vision |
| Portrait Lens | 85–135 mm | Portraits, close-ups |
| Telephoto Lens | > 135 mm | Sports, wildlife, distant subjects |
| Macro Lens | varies (e.g., 100 mm) | Extreme close-ups, 1:1 magnification ratio |
Special Lens Types
Macro Lens: Enables close-up shots with a 1:1 magnification ratio – the subject is projected onto the sensor at the same size as in reality. Especially optimized for minimal distortion and high detail sharpness.
Tilt-Shift Lens: Allows the plane of focus to be tilted relative to the sensor plane. Used in architectural photography to correct converging lines or to create a miniature effect (selective focus).
Mirror Lens: Combines lenses and mirrors for very long focal lengths in a compact design – known from astronomy but also available for photography.
Aperture: An Important Quality Feature
The aperture of a lens indicates how wide the diaphragm can open. It is given as an f-number (e.g., f/1.4 or f/2.8):
- Small f-number (e.g., f/1.4) = bright → good in low light, allows for shallower depth of field
- Large f-number (e.g., f/5.6) = less bright → less light, greater depth of field
Bright lenses are more expensive and heavier but offer more creative freedom and better results in low-light conditions.
Practical Tip
Beginners looking to buy their first interchangeable lens should consider a 50mm standard lens with an aperture of f/1.8. It is affordable, lightweight, very bright, and suitable for almost all subjects – from portraits to everyday shots. It is also the best lens for learning how to creatively use focal length and depth of field.