Lens selection is a process of gradually defining all lens parameters. As an imaging component, a lens, together with light sources and cameras, forms a complete image acquisition system. Thus, lens selection is restricted by the overall system requirements. Analysis and evaluation can generally be carried out from the following perspectives.

The lens operating wavelength and zoom requirement are relatively straightforward to confirm first. Zoom lenses are adopted for applications requiring variable magnification during imaging, while fixed-focus lenses suffice for other scenarios.

In terms of operating wavelength, visible light band is the most common, yet other wavebands are also applicable. Several questions need to be evaluated comprehensively before finalizing the lens wavelength: Is additional filtering required? Is monochromatic or polychromatic light adopted? Can stray light interference be effectively suppressed?

Special requirements derived from practical application scenarios shall be clarified in advance. Examples include measurement functions, demand for telecentric lenses, and requirements for large depth of field (DoF). Depth of field is often overlooked but is an essential factor for every imaging system.

Working distance and focal length are normally evaluated in combination. The general design logic is as follows: Confirm the system resolution first, calculate the magnification based on CCD pixel size, estimate the object-image distance subject to mechanical spatial constraints, and then compute the required lens focal length. Therefore, lens focal length is correlated with working distance, system resolution and CCD pixel size.

The lens image circle must be compatible with the camera sensor size, following the rule that "larger formats are backward compatible with smaller ones". The camera sensor must not exceed the marked image circle of the lens; otherwise, marginal field-of-view image quality will deteriorate. Image quality evaluation mainly focuses on MTF (Modulation Transfer Function) and distortion. Distortion control is particularly critical for measurement applications.

Lens aperture primarily affects image plane brightness. In modern machine vision, the final image brightness is jointly determined by multiple factors including aperture, camera gain, exposure integration time and light sources, leaving multiple adjustable parameters to achieve the target brightness. The lens mount interface refers to the physical connection standard between lens and camera, which must be matched. Adapters shall be used if direct matching is unavailable.

Line scan lenses are paired with line scan cameras. They operate in scanning mode, requiring relative motion between the lens and target. Each exposure captures a single line of pixels, and multiple exposures are stitched into a complete frame. Characteristics of line scan imaging: The resolution along the CCD line array is fixed, while the spatial sampling frequency in the target movement direction depends on the relative motion speed.

From an imaging perspective, line scan lenses have no fundamental difference from other lens types; only the operating method varies.

Micro lenses are deployed in high-resolution scenarios to capture fine target features, featuring short working distances, high magnification and small fields of view.

An object-space telecentric optical path means the chief rays in object space are parallel to the optical axis, with the convergence point of chief rays located at infinity on the object side. Its core function is to eliminate measurement errors caused by inaccurate focusing on the object plane.