Simulation · Physics · Class 12
Astronomical telescope
From the lesson Telescope in Ray Optics and Optical Instruments. Change the values and watch what happens.
Astronomical telescopePhysics · Class 12
The idea behind it
NCERT § "Telescope"
- A refracting (astronomical) telescope has an objective of large focal length and large aperture and an eyepiece of short focal length; it gives angular magnification of distant objects.
- In normal adjustment the final image is at infinity, the magnifying power is m = f_o/f_e, and the tube length (separation of the lenses) is f_o + f_e.
- The final image of an astronomical telescope is inverted.
- A large objective aperture collects more light and improves resolving power, but large lenses are heavy, hard to make free of defects, and can be supported only at their edges.
- Reflecting telescopes use a concave mirror as the objective; this avoids chromatic aberration, and a mirror weighs less and can be supported over its whole back surface.
- In the Cassegrain design the light from the concave primary mirror is reflected by a small convex secondary mirror through a hole in the primary to the eyepiece or detector.
- For a telescope, magnification is about angles, not sizes: the image subtends a larger angle at the eye than the distant object does.