ALPACA will be a wide-field telescope employing an 8-meter rotating liquid mirror. Equipped with a large mosaic CCD camera, it will scan a long strip of sky two and a half degrees wide. As the Earth rotates, all objects in this strip will pass through the field of view of the telescope and be measured.
The optical design is a modified Baker-Paul 3-mirror reflecting system. Light from the 8-meter primary mirror is collimated by the convex secondary mirror, and then refocussed by a concave tertiary mirror. This design gives exceptionally-good images over a very wide field. For the ALPACA design, the images are less than 0.25 arcseconds (RMS spot diameter) over the entire 2.5-degree field of view. Atmospheric seeing will therefore be the primary factor determining the delivered image quality.