Telescopes

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More expensive per inch of aperture

Heavier, longer and bulkier than equivalent aperture Newtonians and catadioptrics.

Small apertures

Less suited for viewing small and faint deep sky objects.

Color aberration due to colors of light bending different amounts.

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Reflectors (mirror)

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Advantages and disadvantages

Lowest cost per inch of aperture

Reasonably compact and portable up to focal lengths of 1000mm.

Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters.

Reasonably good for lunar and planetary work.

Low in optical aberrations.

Open optical tube design allows image-degrading air currents and air contaminants

More fragil

Large apertures (over 8") are bulky, heavy and tend to be expensive.

Slight light loss due to secondary obstruction when compared with refractors.

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Cassegrain reflector

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Catadioptric telescopes

Best all-around, all-purpose telescope design. Combines the optical advantages of both lenses and mirrors while canceling their disadvantages.

Sharp images over a wide field.

Excellent for deep sky observing or astrophotography with fast films or CCD’s.

Very good for lunar, planetary and binary star observing or photography.

Closed tube design reduces image degrading air currents.

Most are extremely compact and portable.

Large apertures at reasonable prices and less expensive than equivalent aperture refractors.

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Schmidtt-Cassegrain

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Problems with earth-based telescopes

Earth’s atmosphere reflects certain wavelengths

x-rays, gamma rays and most UV light is not transmitted by our atmosphere

Earth’s atmosphere blurs images

the bending of light by the atmosphere depends on the temperature of the “air”

“twinkling” (shimmering) effect

“Light pollution”

Solution? Put the telescope in space.

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http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

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Disadvantages of space-based telescopes

Expensive to launch and maintain

Difficult to repair

Low lifetime

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Examples of space-based telescopes