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A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the light is focused.
ome tele opes, known as re telescopes, known as reflectors (Newtonians), use mirrors. Then, the
chmidt- ssegrai elescop ses. Each optical design is briefly discussed below:
evelope in the early 1600s, is the oldest telescope design. It derives its name from the method it uses to focus
ct incoming light rays, hence the name (see Figure 4-1). Early
s acts like a prism and breaks light down into the colors of the
get around this problem, a two-element lens, known as an achromat,
as introduced. Each element has a different index of refraction allowing two different wavelengths of light to be focused at the
ht
New
e back end. There light is bent forward in the tube to a single point, its focal point. Since putting your head in
is
u can
and dust. However, this small drawback does not hamper this type of
lescope’s popularity with those who want an economical telescope that can still resolve faint, distant objects.
S sc fractors, use lenses. Other
Ca n t e uses both mirrors and len
S
D
d the refractor
in li . The refractor uses a l
coming ght rays ens to bend or refra
designs used single element lenses. However, the single len
ainbow, a phenomenon known as chromatic aberration. Tor
w
same point. Most two-element lenses, usually made of crown and flint glasses, are corrected for red and green light. Blue lig
may still be focused at a slightly different point.
Figure 3-1
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tonian reflector uses a single concave mirror as its primary. Light enters the tube traveling to the mirror at
front of the telescope to look at the image with an eyepiece would keep the reflector from working, a flat mirror
called a diagonal intercepts the light and points it out the side of the tube at right angles to the tube. The eyepiece
laced there for easy viewing.
p
Newtonian Reflector telescopes replace heavy lenses with mirrors to collect and focus the light, providing much
more light-gathering power for the dollar. Because the light path is intercepted and reflected out to the side, yo
have focal lengths up to 1000mm and still enjoy a telescope that is relatively compact and portable. A Newtonian
Reflector telescope offers such impressive light-gathering characteristics you can take a serious interest in deep
space astronomy even on a modest budget. Newtonian Reflector telescopes do require more care and maintenance
because the primary mirror is exposed to air
te
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