A 1951 USAF resolution test chart is a

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded as the scale be ...

optical resolution test device originally defined by the

U.S. Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Sign ...

MIL-STD-150A standard of 1951. The design provides numerous small target shapes exhibiting a stepped assortment of precise

spatial frequency In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier tra ...

specimens. It is widely used in

optical engineering Optical engineering is the field of science and engineering encompassing the physical phenomena and technologies associated with the generation, transmission, manipulation, detection, and utilization of light. Optical engineers use optics to solve ...

laboratory work to analyze and validate imaging systems such as

microscopes A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisib ...

cameras A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with a ...

and

image scanner An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting or an object and converts it to a digital image. Commonly used in offices are variations of the desktop ''flatbed scanner'' ...

s. The full standard pattern consists of 9 groups, with each group consisting of 6 elements; thus there are 54 target elements provided in the full series. Each element consists of three bars which form a minimal

Ronchi ruling A Ronchi ruling, Ronchi grating, or Ronchi mask, named after the Italian physicist Vasco Ronchi, is a constant-interval bar and space square-wave optical target or mask. The design produces a precisely patterned light source by reflection or ill ...

. These 54 elements are provided in a standardized series of logarithmic steps in the spatial frequency range from 0.250 to 912.3 line pairs per millimeter (lp/mm). The series of elements spans the range of resolution of the unaided eye, down to the diffraction limits of conventional light microscopy. Commercially produced devices typically consist of a transparent square glass slide, 2 inches or 50 mm in dimension. The slide is printed in metallic chromium by photolithography with the standard pattern, photographically reduced from a large master plot. Slides are available as photographic positive or negative prints to best fit the illumination technique used in various testing methods. A less expensive, abbreviated version omits the two tiniest groups at the center of the pattern (groups number 8 and 9), since the lithography at that scale is costly, and the group elements represent resolution beyond the design of many imaging applications. In practice, the spatial resolution of an imaging system is measured by simply inspecting the system's image of the slide. The largest element observed without distinct image contrast indicates the approximate resolution limit. This element's label is noted by the observer (each group, and each element within a group, is labeled with a single digit). This pair of digits indicates a given element's row and column location in the series table, which in turn defines the spatial frequency of each element, and thus the available resolution of the system. An analytical characterization of resolution as the modulation transfer function is available by plotting the observed image contrast as a function of the various element spatial frequencies. Optical aberrations in the imaging system are readily detected and characterized by translating and rotating the elements within the imaging system's field of view.

Pattern format

The common MIL-STD-150A format consists of six groups in a compact spiral arrangement of three layers. The largest two groups, forming the first layer, are located on the outer sides. The smaller layers consist of repeating progressively smaller pairs toward the center. Each group consists of six elements, numbered from 1 to 6. Within the same layer, the odd-numbered groups appear contiguously from 1 through 6 from the upper right corner. The first element of the even-numbered groups is at the lower right of the layer, with the remaining 2 through 6, at the left. The scales and dimensions of the bars are given by the expression :

\text = 2^,

although usually the following lookup table will be more convenient to use. The line pair (lp) means a black and a white line.

Images

File:USAF-1951.svg, USAF-1951 map, vector format File:SilverFast Resolution Target USAF 1951.png, SilverFast USAF 1951 Resolution Target by LaserSoft Imaging

References

External links

efg's Tech Note: USAF 1951 and Microcopy Resolution Test Charts.

A USAF 1951 resolution chart
in PDF format is provided b

This chart should be printed such that the side of the square of the 1st element of the group -2 should be 10 mm long.

Further explanations and examples

Norman Koren's updated resolution chart better suited for computer analysis {{DEFAULTSORT:1951 Usaf Resolution Test Chart Imaging 1951 establishments in the United States Usaf Resolution Test Chart, 1951 20th-century history of the United States Air Force

Pattern format

Images

See also

References

External links