Telescopes

Activities such as astronomy or nature studies must often be done from a distance. For various reasons we cannot get close enough to the subjects to view them in the detail that is needed. Our eyes are general purpose tools and their resolution is limited, their magnifying properties are minimal and they are limited in how much light that they can gather. We must use optical devices such as telescopes to increase our visual range. A telescope is an optical device which makes far objects appear closer. It samples a small area of view, a field, and then magnifies it so that distant objects appear larger. Parallel light rays entering the telescope are focused to a single point, called the focus or focal point. These focused rays are then magnified with a very powerful lens, or more commonly a set of lenses, called an eyepiece, to give enlarged views of distant objects. The eyepiece acts in the reverse direction to the telescope lens, taking the focused rays and sending them to the eye as parallel rays. The diameter of the observed circle depends on the field of view of the eyepiece.

JODAS allows you to select any One-, Two- Mirror, Catadioptric or Refractor telescope from the pull down menu (located at top) and produces not only a predesign based on third-order aberration theory to your specifications, but perform real raytracing and plot detailed spot diagram and spherochromatic aberration plot, if refracted surfaces are used. All of the telescope designs shown in the telescope tree are descriebed bellow. In the sections that follows I give a brief summary of each design‘s characteristics, advantages, and disadventages to help you decide which designs are most interesting.



JODAS produces preliminary telescopes designs that must be further optimized. This is because the formulae used in the program are based on third order Seidel theory, which is an approximation. Designs begins with choosing what of telescope to design. I stree that different designs require different design procedures. If you have selected the telescope system, your choice influences the input design parameters you will need supply later on in the design process. After click on the Apply button, JODAS will displays the correspond design window.

First however JODAS needs to know the telecope‘s specifications: clear aperture primary and system focal length, the position of the focal plane with respect to the primary. If a corrector is used, you must input primary to corrector distance, corrector thickness and glass type. The program will accept any reasonable input values, but rejects impossible conditions. For example, you cannot specify a system focal length that is less than the focal length of the primary. The half field angle is needed for calculation of secondary mirror size.