3.1 Telescopes
29
Fig. 3.5 Diagram showing the optical pathway of a Schmidt-Cassegrain telescope
optics and will have specialised tools and chemicals to do so; hence you should leave
it to them. If you are using an SCT and are condensating, you might find that slowly
warming the correcting plate with a hair dryer solves the problem, but do not hold
the hair dryer too close. If that is ineffective, the humidity is likely too high for good
observation, in which case it is normally worthwhile shutting the telescope down
until conditions improve.
As with refracting telescopes, reflecting telescopes suffer from optical degradation
due to weather (in fact, due to just being exposed to the air). With time, the thin
silver or aluminium coating on the mirror degrades and will eventually have to be
replaced—re-silvering. This is a relatively easy process (depending on the size, and
replacing the mirror is not as easy as taking it out), but it requires a vacuum chamber,
although many large professional observatories have silvering machinery on site.
3.2 Mounts
Just as important as the optics is the structure to which the telescope is fixed that
allows it to rotate. If the structure is not stable enough, finding an object and keeping
it in the field of view becomes extremely difficult and is perhaps the biggest problem
with the most inexpensive telescopes, which are good only for the Moon and the
brighter planets. A wide array of mounts are currently in use including Dobsonian
(which tends to be shortened to just Dob), German equatorials, GoTo mounts, English
equatorials, and Yoke mounts, although effectively only two designs are in use.
The first mounts were of an altazimuth (alt-az) design, whereby the telescope
is moved around both the vertical (altitude) and horizontal (azimuth) axes. This
design is cost-effective and easy to use. It does, however, have a major drawback.
Astronomical objects appear to move across the sky in an arc as a result of the Earth’s
rotation and its inclination to the plane of the solar system (more on this later). The
effect of this is that in order to track an object with an alt-az mount, the mount
needs to drive both axes in a nonlinear fashion. If it does not, the object soon drifts
out of the field of view. Such tracking is challenging to accomplish by hand and is
29
Fig. 3.5 Diagram showing the optical pathway of a Schmidt-Cassegrain telescope
optics and will have specialised tools and chemicals to do so; hence you should leave
it to them. If you are using an SCT and are condensating, you might find that slowly
warming the correcting plate with a hair dryer solves the problem, but do not hold
the hair dryer too close. If that is ineffective, the humidity is likely too high for good
observation, in which case it is normally worthwhile shutting the telescope down
until conditions improve.
As with refracting telescopes, reflecting telescopes suffer from optical degradation
due to weather (in fact, due to just being exposed to the air). With time, the thin
silver or aluminium coating on the mirror degrades and will eventually have to be
replaced—re-silvering. This is a relatively easy process (depending on the size, and
replacing the mirror is not as easy as taking it out), but it requires a vacuum chamber,
although many large professional observatories have silvering machinery on site.
3.2 Mounts
Just as important as the optics is the structure to which the telescope is fixed that
allows it to rotate. If the structure is not stable enough, finding an object and keeping
it in the field of view becomes extremely difficult and is perhaps the biggest problem
with the most inexpensive telescopes, which are good only for the Moon and the
brighter planets. A wide array of mounts are currently in use including Dobsonian
(which tends to be shortened to just Dob), German equatorials, GoTo mounts, English
equatorials, and Yoke mounts, although effectively only two designs are in use.
The first mounts were of an altazimuth (alt-az) design, whereby the telescope
is moved around both the vertical (altitude) and horizontal (azimuth) axes. This
design is cost-effective and easy to use. It does, however, have a major drawback.
Astronomical objects appear to move across the sky in an arc as a result of the Earth’s
rotation and its inclination to the plane of the solar system (more on this later). The
effect of this is that in order to track an object with an alt-az mount, the mount
needs to drive both axes in a nonlinear fashion. If it does not, the object soon drifts
out of the field of view. Such tracking is challenging to accomplish by hand and is