Cassegrains / SCT's

The Cassegrain format is one of the most common for reflecting telescopes, using a primary and secondary mirror to provide a relatively compact telescope, yet one with significant focal length.

Common modified Cassegrain designs are Maksutov Cassegrain, Ritchey Chretien and Dall Kirkham (corrected) to name but a few. As these varients are quite different, we offer them under there own sections. Here we have options that are closest to the original design.

Classic Cassegrain - These telescopes feature a parabolic primary mirror and a hyperbolic secondary. The hyperbolic secondary results in a scope with minimal spherical aberration. As with all scopes using a parabolic primary, there is coma which is easily dealt with using a coma corrector. Classic Cassegrains have focal ratios from F12 normally which offers minimal field curvature. The small secondary obstruction and excellent sharpness of the Classic Cassegrain make them ideal for planetary use.

The Schmidt-Cassegrain (SCT) is a long established design that offers long focal length for visual and imaging use in a very compact telescope. SCT's use a cheaper and simpler spherical primary and seconday mirrors in their layout. These introduce certain aberrations but when combined with a front corrector plate, they are minimised. The Celestron Edge uses an asperical secondary together with an internal corrector to provide good correction of coma and a flat image field.