Use two flash units at 45 degree angles to the chart as your light source. The largest two groups, forming the first layer, are located on the outer sides. 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. Most lenses are sharper in the center of the frame, especially at wide apertures. One way to test your own lenses is with the USAF lens testing chart.
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