The diagram shows a Newtonian reflector telescope viewing an object at infinity.
ID: 1271979 • Letter: T
Question
The diagram shows a Newtonian reflector telescope viewing an object at infinity. Based on the specs provided on the diagram.
a ) How far outside the tube will the rays come to a focus?
Newtonian telescopes are very long, which can make them unwieldy to move around and point at different objects in the sky. Describe how a Cassegrain telescope could be designed to decrease the total length of the telescope.
How far will the image point move if we use the telescope to observe a bird 50 m from the mirror?
Explanation / Answer
Part a:
as it is a newtonian telescope:
viewing an object at infinity, the image will be formed at focal length, i.e.: 285cm,
tube length = 225cm, so the image will be formed a t a distance:
285-225 = 60 cm.
Part b:
In a symmetrical Cassegrain both mirrors are aligned about the optical axis, and the primary mirror usually contains a hole in the centre thus permitting the light to reach an eyepiece, a camera, or a light detector. Alternatively, as in many radio telescopes, the final focus may be in front of the primary. In an asymmetrical Cassegrain, the mirror(s) may be tilted to avoid obscuration of the primary or the need for a hole in the primary mirror (or both).
It makes use of the special properties of parabolic and hyperbolic reflectors. A concave parabolic reflector will reflect all incoming light rays parallel to its axis of symmetry to a single point, the focus. A convex hyperbolic reflector has two foci and will reflect all light rays directed at one of its two foci towards its other focus. The mirrors in this type of telescope are designed and positioned so that they share one focus and so that the second focus of the hyperbolic mirror will be at the same point at which the image is to be observed, usually just outside the eyepiece.
See image in the web, i am unable to paste one..
Part c:
The movement will be ,miniscule..