The best focus for a GRIN fiber array is shown to occur when the object and image plane vertex distances are equal, even when neither plane is the proper Gaussian unit magnification plane. This analytical result agrees with previous experimental data. With non-Gaussian imaging, the image plane of best focus for the GRIN array is not coincident with the plane of best focus for the individual gradient-index fibers.

Some radiometric properties of gradient-index fiber lenses and lens arrays are explored. Consideration is restricted to the paraxial region of fibers that produce erect images at unit magnification. In two instances the radiometric properties of these lenses and lens arrays are considerably different from the properties of conventional (nongradient) lenses. First, the off-axis image plane irradiance for a single gradient-index fiber falls off far more rapidly than the familiar cos(4) law. Second, the exposure (integrated image irradiance) for a fiber array is independent of the object-to-image distance.

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