Putora Sharpness Indicator Type 7A9

Why is the Putora Sharpness Indicator called "The Magic Chart" by some users? The 7A9 chart has resolution targets from 1 to 9; 10 to 97 lines per millimeter when set up at a standard distance of 60x the focal length of the lens being tested. The frequency circles on the chart that donﾒt resolve will disappear like magic into the gray background making them invisible. The 7A9 Chart is the basic building block of the Sharpness Indicator System. It can be used independently or with the full size background. The 7A9 is useful with film, television, and still optical systems. At 10" x 10" it's a convenient addition to your equipment kit. Use it solo to check sharpness and back focus of any optical system. Use it to check critical focus on a production set. Instructions are included with the chart.