Stepped lens with concentric rings that efficiently focuses light in spotlights and allows smooth, continuous beam adjustment.
Definition
A Fresnel Lens is a special optical lens with concentric, ring-shaped indentations. It is used in Fresnel spotlights to focus and direct light with minimal glass weight and light loss.
Principle of Operation
Optical Functionality
- Concentric Design: Rings function like separate lenses
- Focusing Effect: Directs parallel light to a point
- Weight Reduction: Significantly lighter than a full lens
- Light Loss: Minimal, approx. 2-3% absorption loss
- Sharp Edges: Allows for precise light contours
Zoom Mechanism
Fresnel spotlights have two positions:
- Flood Position: Wide angle, diffuse light
- Spot Position: Narrow angle, concentrated light
The zoom operates by moving the lens relative to the light source.
Practical Application
Fresnel lenses are standard in:
- Studio Fresnels: Universal worklight
- HMI Spotlights: Daylight simulation
- Tungsten Fixtures: Classic film lighting
- Theater Lighting: Broadway and film standard
- Follow Spots: Spotlights with manual control
Size Designations
Fresnel sizes are often designated by lens diameter:
| Size | Diameter | Typical Wattage |
|---|---|---|
| Baby | 3-4 inches | 150-300W |
| Midget | 5-6 inches | 200-300W |
| Standard | 8 inches | 750-1000W |
| Tenner | 10 inches | 2000-10000W |
| Bigeye | Large | 10000W+ |
Maintenance
- Cleaning: Regularly remove dust
- Inspection: Check for cracks or scratches
- Focusing: Regularly check focus
- Lifespan: Very long with good care
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