1951 USAF resolution test chart is a resolution test pattern conforms to MIL-STD-150A standard, set by US Air Force in 1951. It is still widely accepted to test the resolving power of optical imaging systems such as microscopes and cameras, although MIL-STD-150A was cancelled on October 16, 2006^[1]. The pattern consists of groups of three bars with dimensions from big to small. The largest bar the imager cannot discern is the limitation of its resolving power.

Contents 1 Pattern format 2 Problems with the 1951 USAF Chart 3 References 4 External links

[edit] Pattern format

The common MIL-STD-150A format consists of six "groups" in three layers of patterns. The largest groups, forming the first layer, are located on the outer sides. The smaller layers repeat the same pattern but are progressively smaller 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 can be found below and are determined by the equation Resolution (lp/mm) = 2^(Group + ((element-1)/6)).

Number of Line Pairs / mm in USAF Resolving Power Test Target 1951
Group Number
Element	-2	-1	0	1	2	3	4	5	6	7	8	9
1	0.250	0.500	1.00	2.00	4.00	8.00	16.00	32.0	64.0	128.0	256.0	512.0
2	0.280	0.561	1.12	2.24	4.49	8.98	17.95	36.0	71.8	144.0	287.0	575.0
3	0.315	0.630	1.26	2.52	5.04	10.10	20.16	40.3	80.6	161.0	323.0	645.0
4	0.353	0.707	1.41	2.83	5.66	11.30	22.62	45.3	90.5	181.0	362.0	-----
5	0.397	0.793	1.59	3.17	6.35	12.70	25.39	50.8	102.0	203.0	406.0	-----
6	0.445	0.891	1.78	3.56	7.13	14.30	28.50	57.0	114.0	228.0	456.0	-----

^[2]

[edit] Problems with the 1951 USAF Chart

The 1951 chart is not well suited for modern lens analysis. The fragmented arrangement makes it difficult for software to automatically determine the maximum resolution and it does not scale well for testing the corners of lenses where aberrations are more likely to appear. The complex numbering system and use of a look-up chart can be avoided by use of a newer layout chart (the T-21), which labels the groups directly in cycles/mm and is available in the links below from Applied Image. A second version is also available (the T-22) which alters the layout of the bar groups to a mostly straight line pattern, more suitable for scanning. The requirements of MIL-STD-150A are still met because the standard does not specify the pattern group layout.

[edit] References

1. ^ MIL-STD-150A, its Change Notices and the Cancellation Notice are available from http://assist.daps.dla.mil
2. ^ Edmund Optics - 1951 USAF Glass Slide Resolution Targets

[edit] External links

• Applied Image produces standard and custom image test patterns. Improved layout versions of the USAF chart are available (pn T-21 (labeled in cycles/mm) and pn T-22 (labeled in cycles/mm and uses a linear pattern for easier finding and scanning)).
• efg's Tech Note: USAF 1951 and Microcopy Resolution Test Charts.
• Koren 2003: Norman Koren's updated resolution chart better suited for computer analysis
• Max Levy Autograph produces USAF charts in high resolution chrome on opal, UV grade fused silica, and for fluorescent imaging.