There are several possibilities for an optical telescope design to have light gathering power equivalent to that of a 15 metre diameter monolithic mirror telescope. These include a segmented mirror telescope, using as many as ninety hexagonal mirrors; a multi-mirror telescope with six mirrors of over 6 metres diameter; or an array of twenty-five 3 metre telescopes with a common focus. It is the purpose of this paper to show the advantages of an array telescope, these being in summary that: 1) the individual telescopes, using thin meniscus mirrors of short focal length are certainly quite practicable and of low cost; 2) the array is flexible and can be added to without difficulty; 3) the array can be coherent over path lengths of a least 70 metres with existing technology and can have a finite field of at least 5 minutes of arc with good definition; 4) very high resolution interferometry will be possible with such an array, equivalent optically to the VLA in radio wavelengths, as well as the use for photometry, polarimetry, spectroscopy and direct photography or finite field imaging with solid-state detectors.
G. J. Odgers, G. J. Odgers,
"Coherent Array Telescopes As A Fifteen Meter Optical Telescope Equivalent", Proc. SPIE 0332, Advanced Technology Optical Telescopes I, (4 November 1982); doi: 10.1117/12.933547; https://doi.org/10.1117/12.933547