CCTV Lens & Field of View Guide
A CCTV lens's focal length helps determine how wide or narrow the camera view is, but focal length does not determine field of view by itself. Active sensor dimensions, lens design, distortion, cropping, and image processing also affect the final view.
What CCTV Focal Length Means
Focal length is an optical measurement, usually shown in millimeters. In general, a shorter focal length gives a wider view, while a longer focal length gives a narrower view. That comparison is most meaningful when the sensor or active image area is the same.
A 2.8 mm lens is normally wider than a 4 mm lens on the same camera, and a 6 mm lens is normally narrower still. But actual FOV depends on the sensor/image area and the lens implementation. Use the CCTV Lens Calculator when you know the target distance and scene width.
What Is CCTV Field of View?
Field of view is the angular view captured by the camera. Horizontal FOV describes the angle from left to right, vertical FOV describes top to bottom, and diagonal FOV describes corner to corner. These are angular measurements, not physical scene dimensions.
Physical coverage width depends on both the FOV angle and the target distance. The same angular view covers more meters at 20 m than it covers at 5 m. Use the CCTV Field of View Calculator to estimate FOV, scene width, scene height, and pixel density from sensor size, focal length, and distance.
How Field of View Is Estimated
A simple geometric estimate uses an ideal rectilinear model. For horizontal FOV, the formula is:
HFOV = 2 x atan(sensor width / (2 x focal length))
Scene width = 2 x distance x tan(HFOV / 2)
These are geometric estimates. Real published camera FOV may differ because wide-angle lenses can distort the image, cameras may crop or process the active image area, and manufacturers may publish usable FOV differently.
Worked Geometric Example
The following example uses a 5.6 mm sensor width, 3.15 mm sensor height, 2.8 mm lens, and 10 m target distance. Under the ideal geometric model, the approximate results are:
| Horizontal FOV | 90° |
|---|---|
| Vertical FOV | 58.7° |
| Scene width at 10 m | 20 m |
| Scene height at 10 m | 11.25 m |
Example only
This does not mean every 2.8 mm CCTV camera has a 90 degree horizontal FOV. It means this specific geometric input set produces about that result.
2.8mm vs 4mm vs 6mm CCTV Lenses
On the same sensor or active image area, a 2.8 mm lens usually provides a wider view than a 4 mm lens. A 4 mm lens is narrower than 2.8 mm, and a 6 mm lens is narrower still. Narrower views can be useful when the target area is farther away or when more pixel density is needed on a smaller scene width.
Comparing focal lengths is valid only when the rest of the optical system is considered. Sensor size, lens distortion, aspect ratio, image crop, and manufacturer implementation can all change the published result. Avoid treating any focal length as a universal degree value.
Fixed vs Varifocal CCTV Lenses
A fixed lens has one focal length. Its optical field-of-view range is fixed except for digital processing, image crop, or camera settings that alter the active image area. Fixed-lens cameras are simple and common when the coverage requirement is already known.
A varifocal lens has an adjustable focal-length range. It is useful during installation when the exact coverage must be tuned on site. Varifocal does not mean PTZ: a varifocal camera is adjusted to frame the scene, while PTZ cameras actively pan, tilt, or zoom during operation.
Why Camera Sensor Size Matters
The same focal length can produce a different FOV when active image dimensions differ. A larger active sensor width gives a wider horizontal angle for the same focal length, while a smaller active width gives a narrower angle.
Nominal optical-format labels such as 1/2.8 inch do not directly provide one universal exact active width. When accuracy matters, use the manufacturer published horizontal FOV, exact active sensor or image dimensions, and manufacturer lens/design tools.
Field of View and Pixels Per Meter
Pixel density connects the optical view to image detail. The basic horizontal calculation is:
PPM = horizontal image pixels / horizontal scene width in meters
1920 horizontal pixels / 10 m scene width = 192 px/m
Spreading the same resolution across a wider scene reduces pixel density. Narrowing the view or increasing usable resolution can increase pixel density. Use the Pixels Per Meter Calculator when scene width is known.
DORI Planning
DORI is commonly used as a pixel-density planning framework for Detection, Observation, Recognition, and Identification. The commonly applied planning thresholds are:
| Planning Level | Pixel Density |
|---|---|
| Detection | 25 px/m |
| Observation | 63 px/m |
| Recognition | 125 px/m |
| Identification | 250 px/m |
These are pixel-density planning guidelines, not a guarantee of real-world recognition or identification. Lighting, motion blur, camera angle, focus, compression, subject orientation, image processing, and lens quality all affect performance. Use the DORI Distance Calculator for distance estimates from horizontal FOV and image resolution.
Distance and Camera Placement
At greater distance, a fixed angular FOV covers a wider physical scene. As the same number of pixels spreads across more scene width, pixel density decreases. This is why lens choice, FOV, distance, PPM, and DORI should be planned together rather than separately.
Practical placement also includes mounting height, target direction, lighting, expected motion, obstructions, and whether the important target is near the center or edge of the image. A calculator gives the geometric starting point; final camera placement should be verified with the actual camera view.
Common CCTV Lens Planning Mistakes
- Assuming every 2.8 mm camera has the same FOV.
- Choosing lens by megapixels instead of scene width and distance.
- Ignoring target distance.
- Ignoring actual scene width.
- Ignoring pixel density.
- Treating DORI as a guarantee.
- Relying only on diagonal FOV.
- Ignoring manufacturer published FOV.
FAQ
What field of view does a 2.8mm CCTV lens have?
It depends on active sensor/image size, lens design, distortion, and camera processing. In the geometric example on this page, a 5.6 mm wide sensor with a 2.8 mm lens gives about 90 degrees horizontally, but that is not universal.
Is 2.8mm wider than 4mm?
Generally yes on the same sensor or active image area. A shorter focal length usually gives a wider view, but published camera FOV should still be checked.
What does a 6mm CCTV lens do?
A 6 mm lens usually gives a narrower view than 2.8 mm or 4 mm on the same camera, which can put more pixels on a smaller target area or longer distance.
Does sensor size change field of view?
Yes. The same focal length can produce a different FOV when the active sensor or image dimensions change.
How do I calculate CCTV coverage width?
Estimate horizontal FOV from sensor width and focal length, then project that angle at the target distance. The field-of-view calculator does this geometry for you.
What is pixels per meter?
Pixels per meter is horizontal image pixels divided by horizontal scene width in meters. It helps estimate how much detail is available across the scene.
What does DORI mean in CCTV?
DORI stands for Detection, Observation, Recognition, and Identification. It is commonly used as a pixel-density planning framework, not a guarantee of real-world performance.
Related calculators
Estimate focal length from target scene width, distance, and sensor size.
Estimate horizontal/vertical FOV and physical scene coverage.
Check pixel density from image width and scene width.
Estimate DORI planning distances from horizontal FOV and pixels.
References
- Axis Communications: Lenses in surveillance: technical background on surveillance lenses, focal length, field of view, sensor considerations, and lens selection.
- Axis Communications: Pixel density based on IEC 62676-4:2014: background on pixel density and DORI-style surveillance planning thresholds.
- Axis Communications: Pixel density based on IEC 62676-4:2025: updated technical reference on pixel-density planning concepts for surveillance use.