Table of Contents
- Camera Lens Basics
- Fixed Focal Length Lenses
- Varifocal Lenses
- Coverage Area Calculator
- Special Purpose Lenses
- Indian Installation Guide
- FAQ
Camera Lens Basics
The camera lens type determines how wide or narrow an area your CCTV camera covers and how much detail can be seen at distance. Three key parameters: focal length (mm) determines zoom/magnification, aperture (f/stop) determines light sensitivity, and image circle size must match sensor size. For Indian CCTV installations, most cameras use fixed M12 lenses at 2.8mm, 3.6mm, or 6mm focal lengths – choosing correctly for your space prevents costly reinstallation.
Fixed Focal Length Lenses
| Focal Length | Horizontal FOV | Best Use (1/3″ sensor) | India Application |
|---|---|---|---|
| 2.8mm | ~100 degrees | Wide room coverage | Shop interior, lobby, small rooms |
| 3.6mm | ~80 degrees | Standard indoor/outdoor | Most common: corridors, parking, gates |
| 6mm | ~55 degrees | Medium range detail | Number plate reading, counter monitoring |
| 8mm | ~40 degrees | Narrow focus, long range | Compound perimeter, road monitoring |
| 12mm | ~27 degrees | Telephoto detail | ATM camera, jewellery counter detail |
Varifocal Lenses
Varifocal lenses allow manual adjustment of focal length after installation (typically 2.8-12mm range). Advantages: single lens covers multiple use cases, fine-tune coverage after seeing the actual scene, no re-drilling or repositioning needed. Disadvantages: higher cost (Rs 500-1,500 more per camera versus fixed), larger housing, may need refocusing over time as mechanical components settle in Indian heat. Motorised varifocal (available from Rs 4,000+) allows remote focus adjustment via DVR interface – useful for hard-to-access locations.
Coverage Area Calculator
Calculate coverage width at a given distance: Width = 2 x Distance x tan(FOV/2)
Example: 3.6mm lens (80-degree FOV) at 5m distance: Width = 2 x 5 x tan(40 degrees) = 2 x 5 x 0.839 = 8.4m coverage width.
For face identification (recognition at 1m distance), the face must occupy at least 40 pixels width. At 1080p (1920×1080), this means the frame must cover no more than 4.8m width at the target face distance. Use the focal length that gives appropriate coverage for your identification requirement.
Special Purpose Lenses
- Fisheye (1.7-2.1mm, 180+ degrees): One camera covers an entire room including ceiling. Used in Indian retail for single-camera 360-degree shop coverage. Requires dewarping software.
- Pinhole lens (tiny aperture): Hidden camera applications. Used in smoke detector housings and ATM camera bezels.
- IR-corrected lenses: Standard lenses have different focal points for visible vs IR light causing blurry night vision images. Megapixel IR-corrected lenses ensure sharp focus in both day and night modes. Essential for outdoor Indian CCTV with night vision requirement.
Indian Installation Guide
- Gate and compound: 6mm at 5-8m camera height covers a 4-car-width driveway. Use IR-corrected lens for sharp night vision.
- Shop interior: 2.8mm or 3.6mm at ceiling height (3-4m) covers most Indian retail shops in a single camera.
- Staircase/corridor: 6mm pointed down a 10m corridor shows clear face detail at the entrance end.
- ATM/jewellery counter: 12mm provides tight face coverage at 1.5-2m distance for transaction recording.
Frequently Asked Questions
How do I choose between 2.8mm and 3.6mm for indoor use?
2.8mm (approximately 100-degree FOV) is better for small rooms (4x4m or less) and corner mounting where maximum coverage width is needed. 3.6mm (approximately 80-degree FOV) is the standard choice for corridors, parking areas, and most indoor locations. Both are adequate for face recognition at distances up to 3-4m on a 2MP camera.
Do I need varifocal lenses for outdoor CCTV in India?
For most Indian residential outdoor installations with predictable distances (gate, parking, compound boundary), a fixed 3.6mm or 6mm lens is sufficient and more reliable than varifocal. Varifocal is worth the extra Rs 500-1,500 per camera for: commercial locations with multiple camera positioning requirements, locations with uncertain view angles, or when the installation scope is unclear before mounting.
Why does my night vision image look blurry even though daytime is sharp?
Your lens is not IR-corrected. Standard lenses have different focal lengths for visible light (400-700nm) vs near-infrared (700-900nm) – the lens focuses IR at a slightly different point than visible light. IR-corrected (also called megapixel) lenses are designed with compensated glass to focus both visible and IR at the same focal plane. Replace with an IR-corrected lens to fix blurry night vision.
Can I swap lenses between different CCTV camera brands?
Lenses use standardised mounts: M12 (most Indian board cameras and mini-domes), CS-mount (most full-size domes and bullets), and C-mount (professional/industrial cameras). Within the same mount type, lenses are interchangeable across brands. Check if your camera uses M12, CS, or C mount before purchasing a replacement or upgrade lens.
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