USAF resolution chart, original
The 1951 USAF resolution test chart is a resolution test pattern conforming to MIL-STD-150A standard, set by US air force in 1951. It is still widely accepted to test the resolution of optical imaging systems such as microscopes, cameras and image scanners. The pattern consists of groups of three bars (small Ronchi rulings) with dimensions from big to small. The largest bar the imager cannot discern is the limitation of its resolving power.
The common MIL-STD-150A format consists of six "groups" in three layers of patterns. 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
Two patterns are available, 0 - 7 and -2 - 7, produced in accordance with the USAF Resolving Power Test Target 1951 Standard. The most popular range is 0-7 group, with 6 elements per group, an element consisting of two target patterns of 3 lines at 90 degrees to each other, the line space ratio being equal. These charts are produced as a chrome surface image on glass plate. The R70 has an image area of 12 x 12mm on a 51mm square plate and the R71 has an image area of 48 x 48mm on a 75mm square plate. Both plates are 1.5mm thick.
|SR70||USAF resolution chart, original||groups 0 - 7, glass||each||4 weeks||AU $301.00|
|SR71||USAF resolution chart, original||groups -2 - 7, glass||each||4 weeks||AU $403.00|