What do aplanatic optics do?

Aplanatic optics are designed to eliminate both spherical aberration and coma, two major aberrations (image defects) found in telescopes. The end result is sharper images across a much wider field of view than in other designs.

Aberrations are caused by limitations in the design and manufacture of the optics. Designers and optical factories strive to produce affordable telescopes that have as few aberrations as possible. Spherical aberration is caused by rays of light passing at different distances from the center of a lens or mirror not coming to the same focus. Edge rays will typically come to a focus closer to the lens or mirror than central rays. (Corrector plates in Schmidt-Cassegrain telescopes (SCT) are designed to fix this aberration.) Coma is a related effect: it is spherical aberration from rays that come in off-axis. Coma shows up as little off-axis comet-shaped blobs that point inwards towards the center of the field and get bigger as you look towards the edge of the field of view.

Aplanatic optics are superior to SCT optics, which only rely on the corrector plate to get rid of the aberrations in a small area around the center of the field of view. This is especially important for astrophotography, where coma towards the edges of an image can be very noticeable, making apalantic optics the superior choice for capturing astroimages. EdgeHD aplanatic optics maintain diffraction-limited images across the entire field of view of many of the most popular astrophotography cameras.

Updated 11/11/13