The Main Contents And Methods of Optical Lens Inspection

Optical lenses are the core components of optical imaging systems. Their imaging quality and performance directly affect the performance of the imaging system in practical applications. Therefore, it is very necessary to test the various performance indicators of optical lenses.

By testing the performance indicators of optical lenses such as resolution, contrast, distortion, dispersion, and focal stability, we can fully understand the imaging characteristics of the lens and provide data support for lens design optimization, production, manufacturing, and subsequent maintenance.

Ⅰ.The main contents of optical lens inspection

The inspection of optical lenses covers many aspects, mainly to comprehensively evaluate the imaging quality and mechanical performance of the lens. Its main contents include the following directions:

1.Optical performance testing

Resolution testing. Resolution is a measure of the lens's ability to distinguish object details and is the primary indicator of lens imaging quality. By measuring the lens's imaging effect on a standard resolution board, we can intuitively reflect the lens's resolution level.

Distortion testing. Distortion testing primarily detects the geometric deformations that may occur in lens imaging, including barrel distortion and pincushion distortion, which helps evaluate the fidelity of the lens to the image shape.

Color difference testing. Because lenses refract light of different wavelengths to varying degrees, color difference occurs in images. Chromatic difference detection mainly measures the difference in imaging quality of the lens under different wavelengths of light and evaluates the color reproduction ability.

Contrast test. Contrast reflects the degree of contrast between light and dark parts of the lens image. High contrast means the lens can present image details more clearly.

Light transmittance testing. Light transmittance testing mainly measures parameters such as lens transmittance and transmitted light intensity to evaluate the lens's performance in terms of light transmittance.

Optical consistency testing. Optical consistency mainly tests the imaging consistency of the lens under different parameters such as field of view angle and focal length.

Thermal stability testing. This test mainly tests the imaging performance of the lens in extreme environments such as high and low temperatures.

Perform optical performance testing on lenses

2.Appearance quality inspection

Surface flatness inspection. The smoothness and finish of the lens surface directly affects image quality. Checking the surface for smoothness and flatness, and for any obvious bumps, blemishes, or scratches, can help assess the lens's appearance quality.

Detailed size inspection. Check whether the dimensions of key parts such as lens size, aperture, focal length, etc. meet the design requirements.

Coating quality inspection. The coating on the lens surface can also affect image quality. It is necessary to check whether the lens coating is uniform, smooth and free of bubbles or peeling.

Appearance defect detection. Appearance defect detection mainly includes checking whether there are defects such as bubbles, stains, impurities, cracks, etc. on the lens surface.

Assembly quality inspection. Mainly check whether the lens components are firmly assembled and whether there is any looseness or offset.

Abrasion resistance test. This test mainly tests the abrasion resistance of the lens surface to ensure that it is not easily damaged during daily use.

Perform appearance quality inspection on the lens

3.Mechanical properties testing

Focus stability testing. This test verifies whether the lens's focus is stable and whether it drifts or changes under different environmental conditions, such as temperature and humidity. Focus stability testing helps ensure that the lens maintains stable imaging in various environments.

Aperture adjustment test. Check whether the lens aperture is adjusted smoothly and accurately, and whether there is any slippage or movement. The adjustment range, adjustment accuracy, and uniformity of the aperture blades of the lens will affect the amount of light entering the lens and the imaging effect.

Focus speed test. Focus speed refers to the time it takes for a lens to adjust from its current focal length to its target focal length. This test primarily assesses whether the lens's focus speed meets design requirements and its performance in fast and accurate focusing.

Focus ring inspection. This mainly checks whether the lens's focus ring is smooth and sensitive, and whether it is stuck or too loose.

Durability testing. This test examines the durability of the lens by simulating frequent twisting and focusing operations under actual usage conditions to assess its lifespan and stability.

Mechanical performance testing of the lens

4.Environmental adaptability testing

Temperature adaptability testing. This test primarily tests the imaging performance of the lens under different temperature conditions, including antifreeze performance at low temperatures and heat resistance at high temperatures, to assess the lens's adaptability to temperature.

Humidity Adaptability Test. Tests the imaging performance of a lens in high humidity environments. Humidity Adaptability Test helps ensure that the lens maintains good imaging performance in humid environments.

Vibration resistance testing. Tests the stability and shock resistance of the lens when subjected to vibration or impact to ensure it can still function normally in harsh environments.

Waterproof and dustproof performance testing. Mainly tests the waterproof and dustproof capabilities of the lens in harsh environments. Waterproof and dustproof performance testing is key to evaluating a lens's protection level.

Air pressure adaptability test. This test mainly tests the performance of the lens in high altitude or low pressure environments to ensure that the lens can adapt to different air pressure environments.

Ⅱ.Main methods of optical lens inspection

Different methods can be used to inspect optical lenses according to the inspection content and requirements. The following are some common inspection methods:

1.MTF measurement method

The MTF (Optical Transfer Function) measurement method evaluates lens imaging quality by measuring the modulation transfer function of a lens for sinusoidal images of varying spatial frequencies. MTF measurement is primarily used to assess a lens's resolving power and contrast performance. Higher MTF values indicate better imaging quality. MTF measurement is intuitive, quantitative, and easily comparable, making it a valuable tool for evaluating lens imaging quality.

MTF measurement method

2.Interference method

Interferometry is a measurement method based on the principle of light interference. By comparing actual measurement results with theoretical values, a lens's surface accuracy and optical performance can be accurately assessed. Interferometry offers advantages such as high precision, non-contact operation, and rapid measurement speed, making it a commonly used method for optical lens inspection.

3.Geometric optics measurement

The geometric optics measurement method evaluates the mechanical performance of the lens by measuring the lens's focal length, back focus and other geometric parameters. With its advantages of accurate measurement and ease of operation, geometric optics is an indispensable method for testing the mechanical properties of lenses.

4.Environmental simulation method

The environmental simulation method refers to simulating different environmental conditions, such as temperature, humidity, vibration, etc., to evaluate the imaging performance and stability of the lens under these conditions.

Main methods of optical lens inspection

5.Optical performance measurement method

The optical performance of the lens is evaluated by using optical equipment to measure luminous flux, test resolution, and detect color accuracy.

6.Infrared spectroscopy analysis method

The composition, structure and quality of lens materials are analyzed and tested through infrared spectroscopy technology to ensure that the quality of lens materials meets the requirements.