The apparatus is of the first catadioptric order, lighted by a first-class pressure lamp.
Each instrument carries six, five of which can be attached at pleasure either to the catadioptric or the achromatic.
The catadioptric lens, or holophote, gives a far more powerful but a more concentrated beam than the parabolic reflector.
Another classification divides the instruments themselves into three classes: (a) catoptric, (b) dioptric and (c) catadioptric.
Relating to both the reflection and refraction of light, especially by a combination of mirrors and lenses or by a prism. Catadioptric systems are used in Fresnel lenses, optical calibration equipment, and some telescopes. Compare catoptric, dioptric.