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History of the telescope & telescope vocabulary
Transcript of History of the telescope & telescope vocabulary
the refracting telescope
the reflecting telescope
there are two basic types of telescope design...
a refracting telescope uses lenses to bend the light to a single point. This concept is already familiar to most people in the form of a camera lens.
a reflecting telescope bounces light off of mirrors to a single point.
each design has its pros and cons
- image is bright for smaller apertures
- well made lenses yield excellent color
- contrast is also great on quality lenses
-conversely, poorly made lenses will yield bad color, and low contrast.
- because lenses must be very precise, many telescopes can exhibit chromatic aberration.
As light travels through the lenses, it's broken down into the individual colors of the spectrum (like a rainbow). If those colors do not meet at a precise point, white light isn't created. Most typically, violet is the last of the spectrum to join the 'point'. Chromatic aberration is therefore also known as purple fringing.
lends itself to smaller apertures because lenses are expensive and must be made precisely. Large lenses are also heavy and can sag over time.
-glass can be much less precise than refractors
-lends itself well to large formats
-much less expensive to produce
- mirrors will require collimation from time to time
- needs correcting to fix spherical aberration.
fine adjustment of mirrors so that they sit parallel to one another, ensuring that light reaches that perfect point.
telescope mirrors are not flat, this allows light to strike the mirror and reflect back in a cone shape. When the light doesn't form a perfect cone, you have spherical aberration which means the image will appear blurry. Correcting plates made of optically coated glass, as seen on a Cassegrain, will fix this.
Types of Refractors
There are many variations of the refracting telescope, these are based on:
Now for the variations!
number of lens groups & type of glass used
ED (extra-low dispersion)