Test condition of modulation transfer function of optical lens

For the online MTF testing of spaceborne remote sensing cameras, there are already many natural features on Earth that resemble slanted edges, such as coastlines, roads, and bridges. ISO 12233:2023 sets requirements for test conditions (the angle and contrast of the slanted edge). However, for natural features like coastlines, the angle of inclination and the contrast on either side of the coastline are uncertain, making it difficult to meet the requirements for slanted edges specified in ISO 12233:2023. It is necessary to study the MTF test conditions for optical lenses and impose constraints during the measurement process or compensate for the measurement results. The contrast of the slanted edge image captured by the camera is determined by both the intrinsic contrast of the target and the camera’s exposure. Firstly, two sets of slanted edge images are obtained through simulation and their MTF is measured. One set has different contrasts but the same maximum grayscale, while the other set has the same contrast but different maximum grayscale. Next, slanted edge images with different exposures and angles are collected separately and their MTF is calculated. By analyzing the experimental data, conclusions are drawn. To ensure the accuracy of MTF measurement, the camera’s exposure and slanted edge angle need to meet the following two conditions: the slanted edge image should be normally exposed or slightly underexposed; the slanted edge angle is best between 1-10 degrees. If the angle exceeds 10 degrees, the measurement results need to be corrected.