Telescopes Flashcards
(12 cards)
What is normal adjustment?
When distance between lenses is Fo+Fe and the final image is at infinity
What are the disadvantages of a refracting telescope?
1) Chromatic aberration, different colours refract more than others
2) Good quality lenses hard to make and large lenses can get distorted due to their weight
3) Magnification proportional to focal length so larger magnification requires larger telescope
What are the advantages and disadvantages of Reflecting telescope?
1) Mirrors can be supported better so they tend not to distort as much
2) Spherical aberration, if the mirror is not perfectly parabolic then the rays may not converge onto a single point
What type of lenses does a refracting telescope use ?
consists of two converging lenses
What is a Cassegrain telescope and what are its benefits?
Cassegrain telescope is a reflecting telescope that uses a concave and convex mirror. Creates dimmer image since secondary mirror blocks light however it reduces spherical aberration.
What are a ccds?
Charged couple devices, sensitive light detectors used to capture images digitally
Compare CCDs to the eye
1) Quantum efficiency - ratio of detected photons over incident photons is 80% for CCD and only 1% for eye
2) Resolution - eye 500 megapixels vs 50 megapixels for CCDs which have much better spacial resolution
3) Convenience - CCDs produce digital images and can be used remotely
Describe the structure of a Radio telescope
They use parabolic mirror and an antenna at the focal point which is the eye piece equivalent (also manoeuvrable)
What are the advantages of using large diameter telescopes?
Collecting power is proportional to the diameter squared, this allows more fainter objects to be viewed and allows better resolution.
What is minimum angular resolution?
The smallest angular separation for a telescope to distinguish between two points. (depends usually on wavelength)
How can you work the magnification of a telescope?
Angle obtained from the naked eye divided by the angle obtained from the virtual image.
How is Rayleigh criteria related to resolving power?
The smaller the angle is for the Rayleigh criteria, the greater the detail due to greater resolving power
