Sky and Telescope - January 2017 - 6

FROM OUR READERS

A Night on Mount Wilson
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I enjoyed reading about Robert Naeye's
visit to Mount Wilson's 100-inch
reﬂector (S&T: Sept. 2016, p. 22). He
mentions the novel relay lens system to
facilitate viewing through this historic
telescope. However, he didn't go into
detail about its design and function. So
I was curious about its optical conﬁguration and how it converts the system
from f/16 to f/11.3.

100-inch
focal
plane
(f/16)

Meade
152ED
refractor

Astronomer Laszlo Sturmann
replies: As shown at right, the

telescope is used in its Nasmyth conﬁguration and the relay optics are on the outside.
Think of the Meade objective as a very longfocal-length "eyepiece" that, just like any
other eyepiece, forms a real image at the
exit pupil of the telescope. Usually, the exit
pupil of an amateur telescope is just a few
millimeters across. But for the combined
100-inch telescope and Meade objective,
the exit pupil is about 90 mm in diameter. If
the telescope is focused to inﬁnity, the light
passing through the exit pupil is collimated.
So we added a second refractor objective,
from Explore Scientiﬁc, to take in that big,
collimated beam and send it to a conventional eyepiece.

I had no idea that the 100-inch telescope is now available for half- and
full-night rentals, much as the 60-inch
has been. A full night's rental for these
telescopes costs $5,000 and $1,700,
respectively, but both scopes represent

Ritchey and His Telescopes
Although it's true that the Chabot Space
and Science Center in Oakland, California, once housed George Ritchey's
24-inch Newtonian-Cassegrain reﬂector (S&T: Oct. 2016, p. 66), it was
returned to the Smithsonian Institution
several years ago. Also, those interested
in learning more about Ritchey and his
relationship with George Ellery Hale
should track down the deﬁnitive biogra6

J A N U A R Y 2 0 1 7 * SK Y & TELESCOPE

Pupil

The addition of a clever optical relay
system, pictured above and diagrammed
schematically at right, allows the famed
100-inch telescope on Mount Wilson to be
used visually.

a huge bargain if the fee is split among
members of a visiting group. I wish I
lived in California!
Tom Sales
Somerset, New Jersey

It was surprising to learn that many
deep-sky objects fared so poorly through
Mount Wilson's famous 100-inch
telescope. In fact, Naeye notes that he'd
had better views of many of these with
smaller-sized instruments under darker
skies. This only shows that a large aperture is no remedy for light pollution.
Then there were the scope's relatively

phy, Pauper and Prince: Ritchey, Hale, and
Big American Telescopes. Author Donald
Osterbrock beautifully and sympathetically describes Ritchey's great accomplishments while acknowledging his
many personal weaknesses.
Kenneth Lum
San Carlos, California

Author Ted Rafferty replies: In addition to Osterbrock's book, Deborah

100-inch primary mirror

Explore Scientific
ED127 refractor
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Focal
plane
(f/11.3)

poor views of Uranus and Neptune, even
though he rated the seeing at 1 to 1½
arcseconds. With its large aperture, the
telescope was probably looking through
a column of air that contained numerous image-distorting convection cells,
each an estimated 10 to 20 cm across.
In fact, it's often claimed that, when the
seeing is less than ideal, smaller apertures are affected by fewer convection
cells (or perhaps only one) and thus can
provide a more stable image compared to
that from a larger instrument.
Frank Ridolfo
Bloomﬁeld, Connecticut

J. Mills wrote an excellent article titled
"George Willis Ritchey and the Development of Celestial Photography," published in
American Scientist in March 1966.

The "Observer's Challenge"
In February 2009, the Las Vegas Astronomical Society started an online
feature called the Observer's Challenge.
LVAS member Fred Rayworth and I
created this monthly forum to bring

L ASZLO ST UR M A NN (2)

Martin Lewicki
Adelaide, South Australia

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Sky and Telescope - January 2017

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