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Quick Summary Aperture controls how much light reaches a CCTV camera's sensor and how much of the scene stays in focus (depth of field). Selection should be driven by three factors: site lighting levels (lux), depth-of-field requirements, and the target DORI performance level (Detection, Observation, Recognition, Identification). For industrial sites with variable lighting — loading yards, plant perimeters, control-room entrances — the aperture range, control type (auto-iris, manual, or P-iris), and lens focal length must be matched together to reliably meet the site's surveillance objective. |
Aperture is the adjustable opening in a camera lens that regulates how much light reaches the image sensor. It is measured in f-numbers, and the relationship between f-number and aperture width is inverse:
• Lower f-numbers (e.g., f/0.8, f/1.2, f/2.8): indicate a wider aperture, allowing more light in — ideal for low light, but producing a shallow depth of field (only a small range of the scene stays in focus).
• Higher f-numbers (e.g., f/4, f/8, f/16): indicate a narrower aperture, letting in less light — producing a deeper depth of field and reducing the risk of overexposure in bright environments.
A key rule: each full f-stop decrease (e.g., from f/4 to f/2.8) doubles the amount of light entering the lens, while each increase halves it — directly affecting image brightness and clarity under different lighting conditions.
Ambient light level, measured in lux, is the single most important factor in aperture selection:
Lighting Level | Typical Sites | Recommended Aperture |
Low light (0.1–5 lux) | Parking garages, warehouses, alleyways, nighttime outdoor areas | Wide aperture (f/0.8–f/1.8); pair with IR illumination for near-total darkness |
Medium light (5–300 lux) | Lobbies, offices, mixed-light retail spaces, dusk/dawn outdoor areas | Medium aperture (f/2.0–f/4) to balance light intake and depth of field |
High light (>300 lux) | Direct sunlight areas, spaces near large windows/skylights, intense artificial lighting | Narrow aperture (f/4–f/16) to prevent overexposure |
• Shallow DoF (wide aperture): best for focusing on a specific point of interest — doorways, cash registers, access points — isolating the subject from the background, though areas outside the focus range appear blurry.
• Deep DoF (narrow aperture): ideal for monitoring large areas — parking lots, warehouse aisles, intersections — keeping both foreground and background in focus. This requires more light, so it suits bright environments or sites with supplementary lighting.
Aperture choice directly affects a camera's ability to meet its target DORI level — higher DORI levels generally require wider apertures:
• Detection: a medium aperture (f/4) is generally sufficient.
• Observation: a medium-wide aperture (f/4 or wider) is recommended for clarity.
• Recognition: a wide aperture (f/2.8 minimum) is needed to capture clear detail.
• Identification: a very wide aperture (f/1.8 or wider) is critical for sharp, detailed footage.
• Auto-Iris (AI) lenses: automatically adjust aperture in real time for changing light — suited to areas with variable lighting.
• Manual Iris (MI) lenses: fixed aperture set at installation — suited to environments with stable, consistent lighting.
• P-Iris lenses: precise motorized control for optimized depth of field and image quality — suited to high-security applications requiring consistent identification.
Surveillance Scenario | Recommended Aperture | Key Considerations |
Nighttime parking lot / yard | f/0.8–f/1.6 | Prioritize light intake; pair with IR illumination for nighttime clarity |
24/7 monitored entrance (e.g., gatehouse) | f/1.2–f/2.0 (Auto-Iris) | Facial recognition is critical; auto-iris handles day/night transitions |
Daytime facility / warehouse interior | f/2.8–f/4 (Manual Iris) | Balanced depth of field for wide coverage and detail visibility |
Site access road / traffic monitoring | f/1.6–f/2.8 (Auto-Iris) | Wider aperture supports faster shutter speeds to capture clear plates at speed |
Warehouse aisle / storage area | f/2.8–f/4 | Medium depth of field covers shelves while keeping personnel/vehicles in focus |
Perimeter / driveway checkpoint | f/2.8 (Auto-Iris) | Handles variable ambient/evening light; suited to visitor identification |
• Balance the exposure triangle: aperture works together with shutter speed and ISO. In low light, start with a wide aperture, then adjust shutter speed (to minimize motion blur) and ISO (to avoid excessive noise).
• Consider focal length: longer focal lengths (telephoto lenses) require wider apertures to maintain the same light level — for example, a 100mm f/2.8 lens transmits roughly the same light as a 50mm f/1.8 lens.
• Balance budget vs. performance: high-quality wide-aperture lenses (f/0.8–f/1.4) cost more but deliver superior low-light performance; f/2.8–f/4 lenses offer strong value for non-critical areas.
• Test during installation: verify aperture settings on site; for manual lenses, set for the darkest expected conditions to ensure visibility at all times.
• Use lens hoods: in bright environments with narrow apertures, lens hoods reduce glare and improve contrast.
• Evaluate lighting conditions (lux levels) at the installation site, including day/night variation
• Define surveillance goals (Detection / Observation / Recognition / Identification) to determine required image clarity
• Determine depth-of-field needs (shallow for specific points, deep for large areas)
• Select an aperture range based on the above factors
• Choose the appropriate aperture control type (auto-iris / manual / P-iris) based on light stability
• Verify compatibility with the camera's sensor size and lens focal length
Q: What f-number range is best for a poorly lit industrial yard at night?
A wide aperture in the f/0.8–f/1.6 range is recommended, paired with IR illumination to further improve nighttime clarity.
Q: Why does a wider aperture reduce depth of field?
A wider aperture (lower f-number) admits more light but narrows the range of distance that stays in sharp focus, producing a shallower depth of field.
Q: Should a controlled entrance use auto-iris or manual iris lenses?
Auto-iris (or P-iris for high-security applications) is generally preferred for entrances with day/night light transitions, since it adjusts automatically to maintain consistent exposure.
Q: Does aperture alone determine DORI performance?
No. Aperture affects light intake and depth of field, but DORI performance also depends on lens focal length, sensor resolution, and pixel density (PPM) at the target distance.
Future Vision Technology is a China-based manufacturer with 18 years of experience in zoom block, PTZ, and speed dome cameras, supporting global partners through OEM/ODM services. View Product Range
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