Specifications of the optical telescope

Последнее изменение 20 ноября, 2021

Specifications of the optical telescope and its measurements:

The focal length of an optical system basically tells us about how strongly the system converges or diverges the light. For an optical system that is in the air, it basically tells us about the distance over which initially collimated rays are supposed to focus after bouncing back. Systems whose focal lengths are shorter have more optical power than systems with longer focal lengths; That is, it bends the rays more strongly, bringing them to the focus at a shorter distance. In the field of astronomy, the f-Nuber basically denotes the focal ratio which is notated as N. The focal ratio of a telescope is basically defined as the ratio of the focal length of an objective divided by its diameter or by the diameter of an aperture stop in the system.


The instrument’s field of view is controlled by the focal length and the scale of the image that is projected onto the focal plane in an eyepiece, film plate, or CCD. Numerically, the focal ratios which are large are said to be slow or long. Small numbers are fast or short. There are some guidelines that help us to know when to use these terms, and an individual person may create his own guidelines or standards to use these terms. The plano optics produced by the spherical optics company are very accurate, to know more about it visit pfg precision optics. In contemporary astronomical telescopes, any telescope with a focal ratio of slower (larger numbers) than f/12 is generally considered to be slow, and any with a focal ratio of faster (smaller numbers) than f/6. There are more optical aberrations in the systems that are faster that is away from the center of the field of view and they are, in general, demanding more eyepiece designs than slower ones.

For practical purposes in astrophotography, a faster system is often desired for the purpose of collecting more photons over a given time period than a slower system, allowing time-lapse photography results to be processed faster. The use of telescopes that have a wide field of view such as astrographs is done to track the location of the satellites and asteroids that are used in cosmic-ray research and for the astronomical surveys of the sky. It becomes highly difficult to reduce the optical aberrations in telescopes that have low f-ratio in comparison to the telescopes which have larger f-ratio.

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