Horizontal field-of-view estimator
Measure the width you need to cover at the target distance, then compare the exact camera’s horizontal field of view. A focal length such as 2.8 mm does not specify the same view on every sensor. Separate a wide overview from a view intended to show a face or handover.
Choose the lens for its viewing task
| Lens choice | Useful task | Check |
|---|---|---|
| Fixed | A known entrance or room view. | Exact horizontal angle and target detail at the installed distance. |
| Varifocal | Adjust the width during commissioning. | Adjustment range, focus and whether adjustment is manual or motorised. |
| Optical zoom | Capture a narrower view through the lens. | Detail and focus throughout the stated optical range. |
| Digital zoom | Enlarge part of an existing image. | It cannot recover detail absent from the original recording. |
Estimate the width, then check the recording
For a rectilinear lens on level geometry, scene width is approximately 2 × distance × tan(horizontal angle ÷ 2). At 5 m and 90°, this gives 10 m. A 2,560-pixel-wide stream across that width averages 256 pixels/m. These are geometry examples; distortion, viewing angle, compression and light change useful detail. This is not an identification-distance claim.
- Record mounting height, target distance and required width.
- Compare the published horizontal angle for the exact sensor and lens.
- Place a moving subject at the near and far positions; check obstruction, focus and glare.
- Review recorded and exported clips in daylight and after dark before accepting the lens.
Zoom and dual-lens ordering checks
A zoom ratio compares focal-length endpoints; it does not specify an identification distance. Hybrid zoom may combine optical and digital methods. For dual-lens equipment, ask which view is saved, its individual stream resolution, and how zoom and camera control work with the selected recorder. Keep fixed-focal-length comparison and PTZ operation as separate decisions.
Technical background: Axis: lenses in surveillance. The principles do not establish specifications for a QuarkView model. Request a lens configuration with distance, required width, mounting height and day/night viewing task.