On telescope performance evaluation

Abstract

We analyse the imaging performance of synthetic-aperture optical systems (diluted aperture and segmented aperture) using the modulation transfer function. We select a single figure-of-merit, the functional cut-off frequency, over the traditional cut-off frequency, as the most useful one for assessing the optical performance of an instrument for its imaging capacity. A simplified aperture layout is proposed with the performance equivalent to that of the Keck telescope, incorporating a smaller number of segments. The detailed analysis in the spatial frequency plane leads us to observe that the central ring of the hexagons in the Keck telescope does not contribute to its resolution.