Five-lens corrector for Cassegrain-form telescopes

Refractive elements are commonly used on Cassegrain-form telescopes to correct off-axis aberrations and both widen and flatten the field. Early correctors used two lenses with spherical surfaces, but their performance was somewhat limited. More recent correctors have three or four lenses with some including at least one aspheric surface. These systems produce high resolution images over relatively wide fields but often require the corrector and mirrors to be optimized together. Here we present a new corrector design using five spherical lenses. This approach produces high image quality with low distortion over wide fields and has sufficient degrees of freedom to allow corrector to be optimized independent of the mirrors if necessary.