Components · Optics
The lens forms the image the whole system depends on. Focal length sets the field of view, the aperture balances brightness and depth of field, and optical quality decides whether your sensor's resolution is actually used.
Ống kính tạo ra hình ảnh mà toàn bộ hệ thống dựa vào. Tiêu cự quyết định vùng nhìn, khẩu độ cân bằng độ sáng và độ sâu trường ảnh, chất lượng quang học quyết định độ phân giải thực tế.
How it works
Magnification is the ratio between sensor size and the field of view on the part. For a given sensor, a longer focal length gives a smaller field of view at the same working distance; a shorter focal length gives a wider view but more distortion and perspective error.
The aperture (f-number) controls brightness and depth of field. Closing the aperture increases depth of field but reduces light and, beyond a point, diffraction blurs fine detail — especially on sensors with small pixels.
Standard lenses see objects from a single point, so closer objects appear larger. Telecentric lenses collect only parallel rays: magnification stays constant within their telecentric depth, which is essential for accurate measurement of parts that vary in height.
Types
Open each type for how it works, where it fits, its limitations and the specifications to check.
How it works. Available in focal lengths from wide-angle to telephoto. Focus and aperture are set once and locked so vibration cannot change them.
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How it works. Optical design that resolves pixels of around 2–3.5 µm across the full sensor, with low distortion and good corner sharpness.
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How it works. Object-side telecentric lenses accept only rays parallel to the optical axis, so parts look the same size even if they move up or down slightly. Bi-telecentric designs are also telecentric on the sensor side for even lower error.
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How it works. Designed to cover sensors of 4k, 8k, 16k pixels and more with uniform sharpness and illumination along the whole line.
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How it works. Optimized for magnifications around 0.25× to several times, with short working distances and flat field.
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How it works. Zoom or fixed high-magnification optics, often with coaxial illumination ports.
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How it works. A liquid or polymer element changes shape under voltage, refocusing the lens for different distances under software control.
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How it works. Pericentric (360°) lenses view the top and side walls of a part in one image; hole-inspection lenses look inside bores; SWIR and UV lenses are coated and corrected for non-visible wavelengths.
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How it works. Bandpass filters block ambient light; polarizers reduce glare; extension tubes shorten the minimum object distance; protective windows shield the lens in dusty or splashing environments.
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Specifications
| Specification | What it means | How to choose |
|---|---|---|
| Focal length | Distance from the lens to the sensor when focused at infinity. | Calculate from sensor size, field of view and working distance (see the calculator). |
| Sensor format / image circle | The largest sensor the lens covers without dark corners. | Image circle must be at least the sensor diagonal. |
| Mount | Mechanical interface: C, CS, M42, M58, M72, F and others. | Must match the camera, or use an approved adapter. |
| Aperture (f-number) | Size of the lens opening; higher f-number = smaller opening. | Balance brightness, depth of field and diffraction (often f/4–f/8). |
| Resolution | Finest detail the lens can transfer (lp/mm or rated pixel size). | Must match the camera pixel size; see Nyquist in the calculator. |
| Minimum object distance | Closest distance at which the lens can focus. | Check that your working distance is above the MOD. |
| Distortion | Deviation of straight lines in the image, in percent. | Keep low for measurement; can be calibrated in software. |
| Magnification (telecentric/macro) | Fixed ratio between image and object size. | Choose so the field of view fits the sensor with margin. |
| Telecentric depth | Height range over which magnification stays constant. | Must cover the height variation of your parts. |
| Ruggedization | Locking screws, vibration-resistant designs. | Recommended on robots and machines with vibration. |
Engineering tools
Quick estimates based on standard formulas. Always confirm with a test on real parts.
Estimate magnification, focal length, required lens resolution and depth of field from your sensor, field of view and working distance.
Selection guide
| Requirement | Recommended | Why / note |
|---|---|---|
| General inspection, code reading | Fixed focal (FA) lens | Choose focal length from FOV and WD. |
| Precise measurement, height variation | Bi-telecentric lens | Constant magnification, low distortion. |
| 20 MP+ camera, small pixels | High-resolution lens rated for the pixel size | Otherwise the extra pixels add no detail. |
| Webs, long parts, line-scan | Line-scan lens with large image circle | Check mount and magnification. |
| Features below ~20 µm | Macro or microscope lens | Plan lighting for the short working distance. |
| Parts at varying distances | Liquid lens | Software-controlled focus per part. |
| Side walls, inside holes | 360° / hole-inspection lens | One image instead of several cameras. |
| Low light, high speed | Lens with low f-number (bright) | Watch the reduced depth of field. |
Examples
Illustrative setups showing how the components are combined in practice.
Application example
Application example
Application example
FAQ
Both use the same thread, but the flange distance differs (17.53 mm for C, 12.5 mm for CS). A C-mount lens can be used on a CS-mount camera with a 5 mm spacer; a CS-mount lens cannot focus on a C-mount camera.
Because they only collect rays parallel to the axis, the front lens must be at least as large as the field of view.
Often between f/4 and f/8. Wider apertures give more light but less depth of field; very small apertures add depth but diffraction reduces sharpness, especially with small pixels.
Yes — they reduce the minimum object distance and increase magnification, but image quality and brightness drop at large extensions. A macro lens is better for permanent close-up work.
Compare the lens resolution with the sensor's Nyquist frequency (1000 ÷ (2 × pixel size in µm) lp/mm). The calculator on this page shows the value.
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