An enlarged sky image feeds a mini-lens array, typically a few thousands identical lenses each ~ 1 mm diameter.  The lenslet array output is a regular grid of as many small telescope mirror images, which serves as the input for a multi-slit spectrograph that delivers the data cubes. This approach was advocated in the early 1980s, with the first lenslet-based optical TIGER IFS observations in 1987.
