The concepts of optics form the principles required to understand how optical devices, such as telescopes function. Leveraging the knowledge of lenses, which are pieces of glass with curved surfaces, the book explains how images are formed. There are two types of images formed, positive and negative, which are directly correlated to the focal length of the lens. This is also the reason why lenses are â€œpoweredâ€ or â€œnumberedâ€. The following diagram, illustrates these different types of lenses.
Within the realm of telescopes, there are primarily two different types, namely refractor and reflector telescopes. There are advantages and disadvantages offered by both. Whilst it is not possible to list a detailed argument within the scope of this report, there are then aspects which should be considered when deciding on which kind of telescope of use. These aspects are (i) definition, (ii) achromatism, (iii) magnifying power, (iv) light-gathering power, (v) resolving power, (vi) size of image and usable field, (vii) flatness of field, (viii) versatility, (ix) economy and ease of construction and (x) ease-of-use and maintenance (Page and Page, 1966, p.30).