## sábado, 22 de noviembre de 2014

### USAF-1951 target resolution to angular resolution calculator

Abstract
An easy way for testing camera resolution is  to use the USAF-1951 target pattern also called "USAF 1951 Resolving Power Test Target". The aim of this entry is provide an excel calculator to convert from target resolution to angular resolution (cycles per millimetre to cycles per milliradian).

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Although nowadays there are more precise methods for testing camera resolution, the use of the old  USAF-1951 pattern is widely used when testing infrared and visible cameras due to its simplicity and straightforward interpretation.

 USAF-1951 pattern explanation
 USAF-1951 Test Pattern

The USAF-1951 is defined in the military standard MIL-STD-150. The resolution of a particular element in line pairs per millimetre (or cycles per millimetre) can be computed using the following formula.
$$R=2^{K+\frac{N-1}{6}}\\ R: cycles\ \ per\ \ millimetre\\ K: group\ \ number\\ N: Element\ \ number$$

There are, however, a few cases when is desirable to get the resolution in cy/mrad, for example when testing against a collimator and we need to know the camera angular resolution under these units.
For these cases, the excel file USAF 1951 conversion cy-mm to cy-mrad fits like a glove.

REFERENCES
[1] MIL-STD-150A Photographic Lenses
[2] USAF 1951 Chart Standard Layout Product Specifications