Learn the technical terminology of industrial lenses

With the rapid development of science and technology, the machine vision industry has received extensive attention and sufficient industrial applications in various industries with the strong rise of the manufacturing industry. We have to understand the relevant professional terms of machine vision industrial lenses.

1. Telecentric optical system:

Refers to an optical system in which the main ray is parallel to the optical axis of the lens. Light emitted from an object towards the lens, parallel to the optical axis, or even off-axis, is called an object-side telecentric optical system. Light that is directed toward the image from the lens and parallel to the optical axis, or even off-axis, is called an image-side telecentric optical system.

2. Telecentric lens:

A telecentric lens is a lens in which the main light is parallel to the light source of the lens. There are telecentric on the object side, telecentric on the imaging side, telecentric lines on both sides, etc.

The usual shots

The main ray is angled to the optical axis of the lens, so the size of the image changes when the workpiece moves up and down.

The two sides are far from the state of mind

The main object side and image square are parallel to the optical axis of the main ray

The aperture is variable, so you can get a high depth of field, and you can get a more stable image than the object far from the mood head

Suitable for image processing optical systems for measurement, but it is expensive to make it larger

The object is far away from the state of mind

It's just that the main ray of the object side is parallel to the main axis of the lens

The workpiece changes up and down, and the size of the image does not change at all

It is also possible to reduce the size of the coaxial illumination, which is necessary for the use of coaxial illumination

Like Fang Yuan's state of mind

It's just that the image square main ray is parallel to the optical axis of the lens

Even if there is a difference in the mounting on the camera side, it can absorb changes in photographic magnification

For color shift compensation, which is what cameras are supposed to do

3. Characteristics of telecentric optical system:

Pros: Smaller size. Reducing the number of lenses reduces costs.

Disadvantages: When you move the surface of an object up and down, it will change the size or position of the object.

Advantage: When moving the surface of the object up and down, it does not change the size or position of the object. When using coaxial lighting. Smaller sizes are available.

Disadvantages: When coaxial illumination is not used, it is larger than the size of a standard lens.

Advantages: Similar to MML, but with a large difference in the size of the rear end of the lens flange, the accuracy is improved.

Disadvantages: Similar to MML, but more costly than MML.

4. Telecentricity:

Telecentricity refers to the magnification error of an object. The smaller the magnification error, the higher the Telecentricity. Telecentricity has a variety of different uses, and it is important to grasp Telecentricity before using the lens. The main light of the telecentric lens is parallel to the optical axis of the lens, and if the telecentricity is not good, the use of the telecentric lens will not be good; Telecentricity can be easily confirmed using the figure below.

5. Resolution (μm):

The scale of the optical system means that when the black and white grid pattern is observed through the lens, the number of black and white stripes can be distinguished in 1 mm. For example, a resolution of 1 μm means that the closest distance between two points is 1 μm. The following is a formula for calculating the theoretical resolution based on the diffraction of the unphased light of the lens.

6. Resolution(Lines/mm):

Resolution refers to the number of black and white stripes that can be recognized in the 1mm area of the image in the black and white network line diagram lens. The unit of resolving power is lines/mm, for example, 100 lines/mm means that the black-and-white spacing can be recognized at 1/100mm (10 μm). The width of the black and white lines is 1/200 mm (5 μm).

7. Horizontal TV resolution (TV line):

The total number of black and white horizontal lines in the width is equivalent to the height of the vertical height of the TV screen. The ratio of the vertical to horizontal length of the screen is usually 3:4, so the total number of bars in the horizontal width is 3/4. The horizontal resolution of the TV is 240 TV lines, and the total number of horizontal widths of the TV screen is 320 lines. When measuring the resolution of a lens, a set of black and white lines should be considered as a line, but in the case of TV resolution lines, a set of lines should be considered as 2TV lines.

8. Distortion (%):

Distortion is a straight object outside the optical axis, and the lens aberration when it appears as a curve. Lens distortion is also known as lens distortion, that is, the general term for the perspective distortion inherent in optical lenses, which can be divided into pincushion distortion and barrel distortion, the distortion of the straight line towards the center is pincushion distortion, and the distortion that expands outward is called barrel distortion. As shown below:

9. TV Distortion (%):

The image on the TV screen is distorted. The closer the value is to zero, the higher the animal energy.

10. TV Distortion:

The calculated value as a percentage of the actual edge length of the distorted shape to the ideal shape.

11. Aperture efficiency marginal light quantity (%):

Aperture efficiency is the difference in brightness between the optical axis of the imaging disk and the surrounding area when photographing an object of uniform brightness with a lens, measured in percentages (%), assuming a central brightness of 100, which is one of the optical characteristics of the lens.

12. Shielding (%):

Occlusion is the difference in brightness between the center and the edges of a TV screen when using a lens and a CCD-TV lens to capture an object of uniform brightness, in percentage (%). This percentage is typically calculated using the power ratio of the light-receiving module to the CCD module. Occlusion refers to the overall performance of the lens and the TV lens, and the telecentric optical system can be used to reduce the occlusion.

13. Color difference:

In the optical system of a lens, the position and magnification of the image vary with the wavelength of the light. Different wavelengths of light have different colors, which is called color distortion. Distortion on the optical axis is called color distortion. The difference in magnification is called magnification color distortion.

14. Working distance (WD) (mm):

The working distance refers to the distance from the first working surface of the lens to the object to be measured.

15. Object to Imager (O/I)

OI refers to the distance from the object to the plane of the junction.

16. Focal length f(mm) posterior focal length/front focal length

The focal length is the distance from the main point of the optical system to the focal point. The distance from the apex of the *rear lens to the back focus point is the back focal length. The distance from the apex of the first lens to the front focal point is the front focal length.