USAF1951 解析度測試標靶

A USAF 1951 group is resolved when both the vertical and horizontal three-line patterns remain separated.

• Very resolvable: clear and sharp
• Just OK: softer, but still separated
• Not resolvable: blurred together

The finest group that still remains separated is the practical resolution limit of your imaging system.

This product is designed and manufactured according to the US military standard MIL-STD-150A. Its different resolution units use corresponding group and element labels, and the resolution of each unit can be determined by looking up a table. Its applications are wide-ranging, from complex optical systems in aviation, aerospace, and astronomical telescopes to the manufacturing of commonly used optical products in daily life. It is not only suitable for evaluating the imaging quality of various optical instruments and equipment (such as stereo microscopes, collimators, and telescopes), but also highly suitable for evaluating the imaging quality of various lenses and optical components (such as aerial reconnaissance lenses, aerial mapping lenses, projection lenses, microscope lenses, camera lenses, video camera lenses, and industrial camera lenses).

The four-step method is as follows:

1. Installation and Focusing: Place the resolution plate on the focal plane of the system under test (e.g., on the microscope stage, directly in front of the camera), ensuring the plate is perpendicular to the optical axis. Use uniform illumination (front light or backlight) and adjust the focus to achieve the sharpest image. Note: Focus first on the thicker lines, then fine-tune to the finest area to avoid misjudgment.

2. Finding the Limit (Reading): Observe sequentially from the larger group (thicker lines, such as Group 0) to the smaller group (thinner lines, such as Group 7). Find the last group where you can clearly distinguish three independent lines (horizontal or vertical). Record the group number and element number of this pattern.

Criterion: When the lines are blurred and merged into one, or when the three lines cannot be distinguished, it is considered indistinguishable. The limiting resolution at this point is the previous group (the one you can clearly see). 3. Calculate Resolution (lp/mm): Based on the recorded group number (G) and element number (E), obtain the object space resolution value (line pairs/mm, lp/mm) using a formula or table lookup. (Calculation formula: Resolution R = 2^[G + (E - 1)/6])

4. Calculate System Resolution: If you are testing an imaging system (e.g., a camera photographing a resolution chart), magnification must be considered. The system's resolution in the sensor plane (image space) = object space resolution × (image height / object height).

Key Considerations:
Pseudo-resolution: When focusing is severely inaccurate or aberrations are excessive, extremely fine lines that should be blurred may become "sharp" again due to diffraction effects, but at this time the line contrast is extremely low or the position is incorrect. The criterion must be that three lines are clearly countable and have normal contrast.

Directional Differences: The resolution in the horizontal and vertical directions may differ (affected by astigmatism or the sensor); it is recommended to record them separately.

Field uniformity: In addition to the center, the resolution at the edges and corners of the field of view should also be checked to assess the image quality at the lens edges.