Optical telescope
Many types of telescope fold or divert the optical path with secondary or tertiary mirrors. These may be integral part of the optical design (Newtonian telescope, Cassegrain reflector or similar types), or may simply be used to place the eyepiece or detector at a more convenient position. Telescope designs may also use specially designed additional lenses or mirrors to improve image quality over a larger field of view. 
Design specifications relate to the characteristics of the telescope and how it performs optically. Several properties of the specifications may change with the equipment or accessories used with the telescope; such as Barlow lenses, star diagonals and eyepieces. These interchangeable accessories don't alter the specifications of the telescope, however they alter the way the telescopes properties function, typically magnification, apparent field of view and FOV.
List of solar telescopes
This list contains ground-based professional observatory telescopes at optical wavelengths in chronological order. Solar telescopes often have multiple focal lengths, and use a various combination of mirrors such as coelostats, lenses, and tubes for instruments including spectrographs, cameras, or coronagraphs. There are many types of instruments that have been designed to observe Earth's Sun, for example, in the 20th century solar towers were common.