COOLENS DTCM120 Series Bi-Telecentric Machine Vision Lenses for 1/2" Sensors

The COOLENS DTCM120 series consists of bi-telecentric machine vision lenses for industrial cameras with sensors up to 1/2" and a maximum sensor diagonal of 8.0 mm. The lenses are designed for precise optical measurements and inspection applications where constant magnification, high optical resolution and low image distortion are important. The bi-telecentric optical design minimizes perspective errors and maintains nearly constant image magnification, even with small variations in object distance.

The DTCM120 lenses combine high optical resolution with a specified optical distortion of less than 0.1% and telecentricity of less than 0.1°. This makes them suitable for dimensional inspection, edge detection, position measurement and quality control of mechanical and electronic components. The telecentric design is particularly important in applications where height differences or variations in product positioning could otherwise lead to measurement errors.

The series includes 20 lenses with an object-side field of view (FOV) diagonal ranging from 26 to 300 mm and optical magnifications from 0.308x to 0.027x. The working distance ranges from 73 to 465 mm, depending on the selected model. All models feature a standard C-mount camera interface and an adjustable back focal length. The wide selection of fields of view makes the series suitable for inspecting both small precision components and larger industrial products.

Bi-telecentric optical design for precise measurements

With conventional machine vision lenses, the apparent size of an object changes when the distance between the object and the camera changes. This perspective effect can cause measurement errors when components are not positioned at exactly the same height or distance. The COOLENS DTCM120 series features a bi-telecentric optical design, with telecentricity on both the object side and the image side. This keeps optical magnification nearly constant within the telecentric range and significantly reduces perspective-related measurement errors.

Object-side telecentricity is important for dimensional measurements of products with height variations or differences in working distance. Image-side telecentricity ensures that light rays reach the camera sensor almost perpendicular to its surface, contributing to a stable image scale. With a specified telecentricity of less than 0.1°, these lenses are suitable for precise dimensional inspection, diameter and width measurements, edge positioning and applications requiring a consistent image scale. However, the usable measurement depth still depends on depth of field and the required measurement accuracy.

High optical resolution and low distortion

The COOLENS DTCM120 series is designed for industrial cameras that require high-contrast imaging of fine product details and edges. Depending on the model, the specified MTF30 is greater than 175 to greater than 220 lp/mm on the image side. This value represents the spatial frequency at which the lens still transfers 30% contrast. Optical resolution varies between models and must be matched to the pixel size and resolution of the camera sensor. Especially with small-pixel cameras, it is important to verify that the lens provides sufficient contrast for the required measurement or inspection task.

In addition to optical resolution, geometric distortion is an important factor in measurement applications. According to the catalogue, all DTCM120 models have a specified optical distortion of less than 0.1%. This helps preserve straight lines and geometric shapes more accurately than many conventional lenses. This is particularly important when pixel coordinates are converted into real-world dimensions. For applications with demanding accuracy requirements, calibration of the complete camera system is still necessary to compensate for residual optical and mechanical errors.

Lens selection based on field of view and magnification

Selecting the correct DTCM120 lens starts with the required field of view, the camera sensor size and the required object-side pixel resolution. The series offers 20 different models with object-side FOV diagonals ranging from 26 to 300 mm. These values represent the diagonal of the object field, not the width or height of the captured image. With a 1/2" sensor measuring 6.4 × 4.8 mm, the DTCM120-26-AL provides a field of view of approximately 20.8 × 15.6 mm, while the DTCM120-300-AL provides approximately 237 × 178 mm.

Optical magnification ranges from 0.308x for the DTCM120-26-AL to 0.027x for the DTCM120-300-AL. With the same camera sensor, higher magnification results in a smaller field of view and finer object-side pixel resolution. Lower magnification allows a larger product area to be captured, but reduces the amount of object detail represented by each pixel. The required measurement accuracy, minimum defect size and available camera resolution are therefore important factors when selecting a lens. If a larger camera sensor is required, the COOLENS DTCM118, DTCM230 or other DTCM lens series may be a better choice.

Working distance and depth of field

The working distance of the COOLENS DTCM120 series ranges from 73 mm for the DTCM120-26-AL to 465 mm for the DTCM120-300-AL. Working distance is the distance between the front of the lens and the object plane for which the optical system is designed. When selecting a lens, this distance must be matched to the available installation space and the dimensions and position of the product. Working distance does not increase proportionally with the field of view for every model. It is therefore important to check the specified working distance of each individual lens.

The telecentric design provides advantages when inspecting products with height variations, but the usable depth of field still depends on optical magnification, aperture and the required image sharpness. The catalogue specifies F4.2 as the optimum aperture for all DTCM120 models and provides calculated depth of field values at F11 ranging from ±4.6 mm to ±603 mm. These values refer to different optical settings and do not mean that maximum optical resolution is available throughout the complete depth of field. Especially in precision measurement applications, the usable depth of field must be evaluated according to the required edge definition and measurement accuracy. Since the aperture configuration cannot necessarily be adjusted after delivery, the required settings should be confirmed before ordering.

Industrial design and mounting

All COOLENS DTCM120 lenses feature a standard C-mount camera interface. Mechanical dimensions and weight vary considerably between models. The smallest model, the DTCM120-26-AL, has a length of 107.2 mm and weighs approximately 0.3 kg. The largest model, the DTCM120-300-AL, has a length of 622.2 mm and weighs approximately 46.5 kg. Especially with larger lenses, a rigid mechanical mounting structure is essential to prevent deflection, vibration and changes in optical alignment.

All models feature an adjustable back focal length, identified by the AL designation in the model number. This allows precise adjustment of the image-side distance to match the optical configuration and camera sensor. In addition to working distance, lens selection must take into account the overall mechanical dimensions, weight and available mounting options. This is particularly important for larger telecentric lenses integrated into automated measurement and inspection systems.

Key features

• Bi-telecentric machine vision lenses for precise industrial measurement and inspection applications

• Designed for industrial cameras with sensors up to 1/2" and a maximum sensor diagonal of 8.0 mm

• Suitable for industrial CCD and CMOS cameras

• Bi-telecentric optical design with telecentricity on both the object side and image side

• Optical distortion of less than 0.1%

• Telecentricity of less than 0.1°

• MTF30 values greater than 175 to greater than 220 lp/mm, depending on the model

• Nearly constant optical magnification within the telecentric range

• Available in 20 different lens models

• Object-side FOV diagonals from 26 to 300 mm

• Optical magnifications from 0.308x to 0.027x

• Working distances from 73 to 465 mm, depending on the model

• Catalogue-specified optimum aperture of F4.2

• Calculated depth of field values from ±4.6 to ±603 mm at F11

• All models feature an adjustable back focal length (AL)

• Suitable for dimensional inspection, diameter and width measurements, edge detection and precise product positioning

• Industrial housing with model-dependent lengths from 107.2 to 622.2 mm

• Model-dependent weight from approximately 0.3 to 46.5 kg

• Standard C-mount camera interface