How to analyze the MTF curve of industrial lens ?

The analysis of the MTF (Modulation Transfer Function) curve of an industrial lens is an important method to evaluate the image quality of the lens. The MTF curve can intuitively show the contrast reduction of the lens and the resolution of the lens at different spatial frequencies. The following is a detailed analysis of the MTF curve:

First, the meaning of MTF curve

MTF curve is a graphical representation of lens performance. It comprehensively reflects the contrast and resolution characteristics of the lens, and is currently recognized as a relatively scientific method for analyzing the image resolution ability of the lens. The MTF curve shows the lens's restoration of contrast, the vertical axis indicates the quality of contrast (the value range is usually 0 to 1, the closer to 1 means the better image quality of the lens), and the horizontal axis indicates the distance from the imaging center (the unit is usually in millimeters, indicating the distance from the center of the lens to the edge of the lens).

Second, the composition of MTF curve

1. Solid line (S curve) :

• Indicates the imaging performance of shooting radiating patterns from the center.

• Usually denoted by the letter "S", which stands for MTF properties in the radial (sagittal) direction.

2. Dashed line (M curve) :

• Indicates the imaging performance of the shooting line in concentric circles extending outward.

• Usually denoted by the letter "M", it represents the MTF property in the tangential (meridian) direction.

Three, MTF curve analysis points

1. Curve height:

• 10 lines/mm curve: reflects the image contrast of the lens. The closer the curve is to 1 (the maximum), the better the image contrast of the lens.

• Curve of 30 lines/mm: reflects the resolution of the lens. The closer the curve is to 1, the higher the resolution of the lens. The unit "line/mm" means how many white and black stripes there are in 1 mm width.

2. Curve shape:

• The slower the MTF curve decays from left to right, the better, indicating that the imaging gap from the center of the lens to the edge is small, that is, the edge imaging performance of the lens is more consistent with the center imaging performance.

• If the curve suddenly drops at a certain spatial frequency, it may indicate that the lens has some kind of aberration or defect at that frequency.

3. How close the solid line is to the dotted line:

• The closer the solid line is to the dotted line, the closer the MTF performance of the lens in the two vertical directions, that is, the smaller the astigmatism of the lens and the more uniform the image quality.

• If the solid line is far from the dashed line, it may indicate aberration or distortion in a certain direction of the lens.

4. Performance at different apertures:

• MTF curves are usually tested at different apertures. In general, the MTF value at the maximum aperture may be slightly lower than the MTF value at the best aperture (such as F8).

• The imaging performance of the lens at different apertures can be evaluated by comparing MTF curves at different apertures.

4. Application of MTF curve

1. Lens selection:

• When choosing an industrial lens, you can choose a lens with better image quality by comparing the MTF curves of different lenses.

• Especially for applications that require high resolution and high contrast, the MTF curve is an important reference.

2. Lens optimization:

Lens manufacturers can analyze the MTF curve to find out the shortcomings in the lens design and optimize and improve it.

• For example, the MTF value of the lens can be increased by adjusting the lens combination, optimizing the coating process, etc.

3. Imaging quality assessment:

• In practical applications, the MTF curve of the lens can be measured to assess whether its image quality meets the requirements.

• If you find that the MTF curve is not performing well at a certain spatial frequency, you can further check whether there are problems with lens installation, focusing, etc.

In summary, MTF curve is an important tool to analyze the image quality of industrial lenses. Through in-depth analysis of MTF curve height, shape, close to the solid line and dotted line and performance at different apertures, the imaging performance of the lens can be comprehensively evaluated, providing strong support for lens selection, optimization and image quality evaluation.