Secondary
mirror
(flat)Secondary mirror
(hyperbolic)EyepieceEyepieceEyepieceIncoming
lightPrimary mirror
(parabolic)Primary mirror
(parabolic)Primary mirror
(parabolic)Focused
imageEllipseCircleParabolaHyperbolaCircle Ellipse
Parabola
x HyperbolayWWW.ASTRONOMY.COM 33
As he, Hale, and Adams argued over the proper
design, Ritchey, who had befriended Hooker and
gained his confidence, quietly made his case in no
uncertain terms. He had come to the opinion that Hale
and Adams had no idea what they were talking about.
Hale later learned of Ritchey’s circumvention of his
authority and promptly demoted him from lead on the
100-inch project, relegating him to the optical shop
where he would remain until the 100-inch primary
mirror was finished, polished, and tested for use in
the telescope. The highly persuasive director then
convinced Hooker that the original parabolic design
was perfect for his new telescope. Hale’s reputation as a
scientist, instrument designer, and observatory builder
doomed Ritchey, who lacked the poise and power of
persuasion of the Mount Wilson director. Hooker soon
relented and died not long after, leaving Ritchey to his
fate. He had bitten the hand that fed him and his days
at Mount Wilson were numbered.
When Ritchey was forced to depart Mount Wilson
in the fall of 1919 — just as the likes of Edwin Hubble
and Milton Humason were beginning highly profitableTELESCOPES
AND MIRRORS
In a reflecting telescope, the prime focus
is the point where light rays bouncing off
the primary mirror create a clear image in
front of the primary. But this is typically
an inconvenient place to focus light. A
secondary mirror, placed in the path of
light reflected from the primary mirror,
can focus the image elsewhere. Light
focuses at the Newtonian focus when the
secondary mirror deflects light off to the
side of the telescope. Alternatively, the
secondary mirror can send light back
toward the primary mirror to focus at a
point just behind the primary: the
Cassegrain focus.
The primary and secondary mirrors
can have various shapes. Parabolic and
hyperbolic surfaces represent the
geometric sections of a cone intersected
by a plane. In essence, parabolas and
hyperbolas are slices of the cone, taken
from different places. In the case of a
parabola, the plane intersects parallel
to one side of the cone. To create a
hyperbola, the plane must intersect
both surfaces of a double cone
at a steeper angle, often
perpendicular to the bottom
of the cone and parallel to
its axis of rotation. — R.V.,
Alison Klesman
Parabolas and hyperbolas are conic sections, which mean they are curves created by taking slices through
a cone. A parabola results from the intersection of a plane parallel to one side of the cone. Inserting a plane
at a steeper angle creates a hyperbola. ASTRONOMY: ROEN KELLYPRIME FOCUS NEWTONIAN FOCUS CASSEGRAIN FOCUS