Explain industrial lens selection

Choosing an industrial lens involves careful consideration of various factors, including the lens's optical quality, material, precision, and lens structure. Industrial lenses can differ significantly in terms of imaging quality, even within the same type of lens, due to these factors. This also leads to a wide range of prices, from hundreds to tens of thousands of yuan. Common lens types include the four-element, three-group Tessar lens, and the six-element, four-group Double Gauss lens. When evaluating lens quality, manufacturers typically use the Optical Transfer Function (OTF), which includes the Modulation Transfer Function (MTF) and Phase Transfer Function (PTF). Here's a comprehensive guide on selecting industrial lenses, with a focus on key considerations and common optical aberrations.

Common Optical Aberrations

Optical aberrations affect image quality. Here are six common types of aberrations:

1. Spherical Aberration: This occurs when light rays from a single monochromatic cone emitted from a point on the optical axis do not converge at the same point after refraction through the optical system. This results in a diffuse light spot, also known as a blur circle.

2. Coma: When light rays from an off-axis point source refract through the optical system, they may form a comet-shaped light spot with a bright tail, known as coma aberration.

3. Astigmatism: This happens when light rays from an off-axis point source do not form a sharp point after refraction through the optical system but instead create a diffuse light spot.

4. Field Curvature: This occurs when the image of a flat object does not lie on a flat image plane but instead on a curved surface. This leads to blurred edges when the center is in focus and vice versa.

5. Chromatic Aberration: This occurs when light rays of different wavelengths refract differently through the optical system, resulting in color fringes around objects.

6. Distortion: This is a geometric aberration where straight lines become curved after passing through the optical system. Distortion doesn't affect image sharpness but alters its geometry.

Practical Parameters for Evaluating Industrial Lenses

When assessing industrial lens quality, several practical parameters come into play:

1. Resolution: The ability to clearly distinguish fine details in the subject. It's often measured in line pairs per millimeter (lp/mm).

2. Acutance: This refers to image contrast between the brightest and darkest areas.

3. Depth of Field (DOF): The range of distance within which the image remains relatively sharp. It indicates how much of the scene can be in focus at once.

4. Maximum Relative Aperture and Aperture Scale: The relative aperture is the ratio of the lens's entrance pupil diameter (D) to its focal length (f), represented as D/f. The inverse of relative aperture is called the aperture scale, indicated on the lens, like f/1.2. Larger apertures allow more light and are useful for low-light conditions or shorter exposure times.

Interactions Between Parameters

Here are some general rules for understanding the relationships among different lens parameters:

1. Focal Length:

   • Shorter focal lengths increase depth of field but also increase distortion and vignetting.
   • Longer focal lengths decrease distortion and increase depth of field.

2. Aperture Size:

   • Larger apertures increase brightness, resolution, and depth of field but may decrease image quality at the edges.

3. Image Center vs. Edges:

   • Typically, the center has higher resolution and illumination compared to the edges.

By understanding these principles, you can make informed choices about which industrial lens best suits your needs and achieve optimal results with the right lens selection.