Digital Camera Lenses
Summary
From standard primes to fisheyes: A comprehensive breakdown of lens types, focal lengths, and optical defects (distortion, flare). Includes a mind map for lens classification and maintenance tips.
Overview
mindmap
root((Lens))
Properties
Aperture
Focal Length
Types
Standard
Wide-angle
Telephoto
Zoom
Macro
Fisheye
Issues
Flare
Distortion
Focus
Fixed
Variable
Auto
Imaging Principle
Convex Lens Rule: Single focal length determines virtual/real image; double focal length determines size.
Basic Functions
- Converge light beams to create image on film/sensor
- Collect large amount of light for proper exposure
Inherent Properties
Speed / Aperture
| Term | Description |
|---|---|
| Fast Lens | Large max aperture (f/1.4-f/2.8), allows more light |
| Slow Lens | Small max aperture (f/4-f/5.6), allows less light |
Focal Length
The distance from lens center to sensor where a clear image forms.
| Characteristic | Effect |
|---|---|
| Longer focal length | Higher magnification, smaller scene in frame |
| Shorter focal length | Lower magnification, wider scene in frame |
Focus Types
| Type | Description |
|---|---|
| Fixed Focus | Clear image for objects beyond minimum focus distance |
| Variable Focus | Manual focus ring adjustment |
| Auto Focus | Camera automatically adjusts focus |
Lens Categories
Key Principle: Longer focal length = Smaller angle of view
For 35mm format (diagonal 43mm), standard lens is approximately 50mm.
Comparison Table
| Type | Focal Length | Angle of View | Best For |
|---|---|---|---|
| Wide-angle | < 35mm | Wide | Landscapes, architecture |
| Standard | 35-70mm | Normal | General, street |
| Telephoto | > 70mm | Narrow | Sports, wildlife |
| Portrait | 85-135mm | Moderate | Headshots |
Telephoto Lens
Characteristics:
- Expensive
- Heavy
- Less stable (requires faster shutter)
Handheld Rule: Shutter speed should be at least 1/focal length for sharp handheld shots.
(e.g., 200mm lens → minimum 1/200s)
Zoom Lens
Two control rings:
- Focus control
- Focal length control
Disadvantages:
- More expensive than primes
- Bulky and heavy
- Less sharp than prime lenses
Best Practice: Focus at maximum zoom, then adjust focal length for composition.
Macro Lens
For extreme close-up photography with high reproduction ratios.
| Type | Reproduction Ratio |
|---|---|
| True Macro | 1:1 (life-size) |
| Micro Focus | 1:1.2 ~ 1:2 |
| Close Focus | 1:2 ~ 1:4 |
Common focal lengths: 50mm, 100mm
Macro photography has extremely shallow depth of field (~1 inch), requiring precise focus.
Fisheye Lens
- Ultra-short focal length
- ~180° angle of view
- Lines radiate from center; only center lines remain straight
Common Lens Issues
Flare
Bright light reflects off lens surface, creating ghosting artifacts.
Solutions:
- Anti-reflective coating
- Lens hood
Perspective Distortion
| Issue | Cause | Solution |
|---|---|---|
| Wide-angle distortion | Close subjects appear stretched | Use longer focal length |
| Big nose effect | Portrait too close with wide lens | Step back, use 85mm+ |
| Telephoto compression | Distant objects appear same size | Expected behavior |
| Flat face effect | Portrait too far | Get closer, use 85-135mm |
Linear Distortion
Parallel lines appear non-parallel in tall structures (converging verticals).
Solution: Keep camera back parallel to building facade.
Lens Care
Don’t blow on lens surface — saliva droplets can damage coating!
Proper cleaning:
- Use professional lens tissue or microfiber cloth
- Use lens-specific cleaning solution
- Clean in circular motions from center outward