I. Basic Lens Parameters

The 6mm lens paired with a 1/2.7 "–1/2.8" sensor is the most commonly used medium-to-long focal length combination in security and facial recognition applications. Its key advantage is that it provides an optimal balance between coverage width and recognition range.

Reference comparison:

· • 4mm → Suitable for close-range distances of 2–5 m; offers a wide field of view, but the facial feature pixels are relatively small.

· • 6mm → Suitable for medium range (3–8 m); a balanced choice (Recommendation: ⭐⭐⭐⭐⭐)

· • 8mm → Suitable for long-range distances of 5–12 m; narrow field of view

II. Quick Reference Table of Core Installation Parameters

III. Detailed Installation Height Guidelines

3.1 Scope and Rationale

Core principle: Position the face slightly below the center of the frame to minimize facial distortion caused by an overhead viewing angle. An excessively high mounting height can result in an overly steep angle, causing the camera to capture only the top of the head and the forehead; conversely, an excessively low mounting height may lead to obstructions or create a sense of pressure for pedestrians.

3.2 Scenario Adaptation Recommendations

· • High proportion of children (height 1.2–1.4 m) → appropriately reduce to 2.0–2.2 m

· • Primarily adult males (1.7–1.85 m) → Recommended height: 2.4–2.6 m

· • Mixed population → Suitable for all users up to 2.4 m

3.3 Quick Calculation Formula

Installation height ≈ average height of the target population × 0.88 + safety margin

Example: Average height of 1.70 m → 1.70 × 0.88 + 0.5 ≈ 2.0 m (on the lower end)

After optimization, the recommended range is 2.2–2.4 m, ensuring that the face of a person 1.85 m tall remains within two-thirds of the frame.

IV. Detailed Explanation of the Downward Angle (Inclination Angle)

4.1 Recommended俯角 for different scenarios

4.2 Hazards of an Excessive Downward Angle (>20°)

When the俯角 exceeds 20°:1) Only the top of the head and the forehead can be captured, and the face is severely compressed; 2) Insufficient pixel coverage is observed in the region below the nose; 3) The facial pitch angle exceeds the algorithm's tolerance range (typically ±15°); 4) The recognition rate may drop from 98% to below 60%.

4.3 Quick Reference Mnemonic for Angle Adjustment

The camera lens is centered on the point on the target's face where it approaches, at a height of approximately 1.5 m above the ground.

operating steps:

1. 1. The camera is installed at a height of 2.4 m.

2. 2. The target is located at 4 m (the midpoint of the channel).

3. 3. Align the lens with this spatial point (4 m, 1.5 m)

4. 4. Calculate the inclination angle: arctan((2.4–1.5)/4) ≈ arctan(0.225) ≈ 12.7°

5. 5. Falls within the recommended range of 10°–15° ✅

V. Distance and Coverage Table

The following data are calculated based on a 1/2.8" sensor paired with a 6 mm lens (HFOV ≈ 47°):

Calculation formula: coverage width ≈ 2 × distance × tan(HFOV/2)

Example: For a 6 mm beam at a distance of 5 m → 2 × 5 × tan(23°) ≈ 2 × 5 × 0.425 ≈ 4.25 m

VI. Installation Scenario Classification Scheme

Scenario A: Passage/Corridor (unidirectional pedestrian flow)

The camera is installed on one side of the passageway, positioned to capture an overhead view of the incoming pedestrian flow. The installation height is 2.4 m, the俯角 is 12°, and the optimal capture point is set at 4–5 m.

· ✅ Recommended: Install on one side of the passageway, directly facing the flow of people approaching from that side.

· ✅ Capture distance setting: 4–5 m

Scenario B: Entrances/Exits / Main Gates

The camera shall be installed 3–4 m inside the door, directly facing the entrance direction. The installation height shall be 2.4 m, with a downward tilt angle of 12°. Avoid backlighting; if the main door faces outdoors, supplemental lighting or a wide dynamic range setting should be employed.

· ✅ Recommended: 3–4 m inside the gate, directly facing the entrance direction

· ⚠ Note: If the main door faces outdoors, supplemental lighting or wide dynamic range (WDR ≥ 120 dB) is required.

Scenario C: Turnstile/Time & Attendance Machine (Station Detection)

If the camera is positioned more than 3 m from the turnstile, a 6 mm focal length is appropriate, with the俯角 (tilt angle) controlled between 0–5°. If the distance to the turnstile is only 1–2 m, it is recommended to switch to a 4 mm lens.

VII. Common Pitfalls and How to Avoid Them

❌ Error 1: Installing it too high without adjusting the angle

Height: 3 m;俯角: 5° → Face located in the lower 1/4 of the frame → Severe distortion; low recognition rate

· ✅ Countermeasure: For every 0.1 m increase in height, the downward angle increases by 1°.

❌ Error 2: Backlight installation

Camera facing the door/window → entire face appears black

· ✅ Mitigation: Use side mounting or add fill lights, or opt for a camera with wide dynamic range (WDR 120dB+).

❌ Error 3: Incorrect determination of installation distance

I thought a 6mm lens could capture up to 20m → in reality, beyond 8m, only half of my face is visible.

· ✅ Mitigation: For 6mm lenses, the maximum capture distance shall not exceed 8–10 m.

❌ Error 4: Excessive horizontal deflection angle

Camera shot in a diagonal angle from the side of the passageway → face yaw> 45° → algorithm fails to recognize

· ✅ Countermeasure: Horizontal deflection ≤ 20°, not exceeding 30° at the farthest point

VIII. On-site Commissioning Steps (Practical Procedure)

Step 1: Secure the camera at a height of 2.4 m (tighten the support bracket)

Step 2: Stand at a distance of 3–5 m, then adjust the俯角 until your face occupies the upper third of the frame.

Step 3: On the platform, inspect the face detection bounding box: Is the bounding box stably enclosing the entire face? Is the detected face pixel width ≥ 120 px?

Step 4: When a person approaches from a distance, check the captured trigger point: the ideal trigger distance for the 6mm lens is set between 3–8 m.

Step 5: Test with different heights: 1.6 m / 1.7 m / 1.8 m (one trial per height)

Step 6: Adjust the fill light brightness (avoid overexposure or underexposure)

On-site Quick Verification Formulas

Given the installation height H, the downward angle θ, and the target distance D:

The horizontal position of the face in the frame ≈ H-D × tan(θ)

Example: H=2.4 m, θ=12°, D=4 m → 2.4 − 4×tan(12°) = 2.4 − 0.85 = 1.55 m

→ The camera captured the pedestrian at a height of 1.55 m, which precisely corresponds to the facial region ✅