What is a good MTF?

Understanding Modulation Transfer Function (MTF)

Modulation Transfer Function (MTF) is a measure of the optical performance of a lens or imaging system. It quantifies the system's ability to reproduce (or transfer) detail from the object to the image. Specifically, MTF describes how well a system can reproduce various levels of detail under different lighting conditions.

MTF is represented as a curve, showing the contrast (modulation) of the output image as a function of spatial frequency (detail level). Spatial frequency is measured in line pairs per millimeter (lp/mm), indicating the number of alternating black and white lines that can be resolved per millimeter.

Criteria for a Good MTF

A good MTF curve would exhibit the following characteristics:

• High Contrast at Low Frequencies: This indicates that the lens can reproduce large details with high contrast.
• Gradual Decline: A gradual decline in contrast as spatial frequency increases. A steep drop-off indicates a loss in the ability to reproduce finer details.
• Consistency Across the Frame: Good lenses show minimal variation in MTF performance from the center to the edges of the frame.

However, interpreting MTF charts requires understanding that no lens is perfect, and trade-offs are often made between different aspects of lens performance, such as sharpness, contrast, and chromatic aberration.

Conclusion

In summary, a good MTF is indicative of a lens's ability to render sharp, detailed images with high contrast, especially at lower spatial frequencies. While higher values across all frequencies are desirable, a balanced performance that maintains detail without sacrificing image quality is often more practical.