Ten parameters of telecentric lens

Telecentric lens (Telecentric) is a high-end optical lens designed to correct the parallax of traditional lenses. Compared with general lenses, it has absolute advantages in terms of magnification, distortion, parallax, and resolution. Let's talk about the ten parameters of telecentric lens selection.

Parameter 1: Telecentricity

Telecentricity refers to the error of the magnification of the object. The smaller the magnification error, the higher the telecentricity. There are various uses for telecentricity, and it is important to grasp telecentricity before using the lens. The main light of a telecentric lens is parallel to the optical axis of the lens. If the telecentricity is not good, the use effect of the telecentric lens is not good. The telecentricity can be easily confirmed with the following figure.

Parameter 2: Resolution (μm)

The scale of the optical system capability indicates the maximum logarithm of the black and white stripes that can be observed and observed in 1mm when the black and white grid pattern is observed through the lens. The resolution is the measurement value of the closest distance that can be approached before two points cannot be identified. For example, a resolution of 1 μm means that the closest distance that can be approached between two points is 1 μm.

Parameter 3: Resolution (Lines / mm)

The resolution refers to the number of recognizable black and white stripes in a 1mm area in the image in the black and white network map lens. The unit of resolution is line / mm. For example, 100 line / mm represents the recognizable black and white pitch of 1 / 100mm (10 μm). The width of the black and white lines is 1/200 mm (5 μm).

Parameter four: distortion (%)

Distortion is a straight object off the optical axis, and lens aberrations when presenting a curve. Lens distortion is also called lens distortion, which is a general term for perspective distortion inherent to optical lenses. It can be divided into pincushion distortion and barrel distortion. The straight line toward the center is called pincushion distortion. Barrel Distortion.

Parameter five: depth of field

Depth is when the object moves back and forth from the best focus. The distance between the closest point and the furthest point where the sharpest focus appears. The depth range on the object side is called the depth of field. Similarly, the range on the camera side is called the depth of focus. The value of the specific depth of field is slightly different. Depth of field can be calculated using the following formula:

Depth of field = 2 x Permissible COC x effective F / optical magnification 2 = allowable error value / (NA x optical magnification) (using 0.04mm Permissible COC)

Parameter six: depth of focus

Depth is the distance between the closest point where the sharpest focus appears and the farthest point when the CCD moves back and forth from the best focus. The depth range on the image side is called focal depth.

Parameter seven: optical magnification

Magnification means that the size of the original imaging area of the subject can be changed by adjusting the lens. Optical magnification is the magnification that can be changed by an optical lens. Relationship between main points and imaging: Magnification refers to the ratio of imaging size to the object.

Parameter eight: resolution

Shows that you can see the interval of 2 points 0.61x using wavelength (λ) / NA = resolution (μ). The above calculation method can theoretically calculate the resolution, but does not include distortion. ※ The use wavelength is 550nm.

Parameter 9: Edge brightness

The contrast degree refers to the percentage of the illuminance in the center and the illuminance in the periphery.

Parameter ten: zoom lens

Variable focal length lenses, magnifications, and imaging ranges can be easily changed. It is suitable for situations where you need to find the most suitable shooting conditions (shooting distance, focal length of the lens) for easy operation. A zoom lens does not cause a focus position shift, and a zoom lens causes a focal position shift.

After we understand these parameters, we will no longer be able to read them, and we will know more about lens selection for machine vision projects.