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.
Copyscope
A copyscope is type of refracting telescope that can be made by hand rather than bought in which the objective lens comes from an old photocopy machine, hence the origin of the name. The lenses usually come from defective or old photocopiers, allowing for the objective to be obtained for free or at a low cost. They are usually modest aperture lenses, ranging from 50mm to 60mm, of short focal length, good for use in a portable, wide-field telescope, but unsuitable for higher magnifications. Given the use of good components, however, a copyscope can become a rich-field instrument capable of reaching many extended objects and even star fields.