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Transcript
TELESCOPE REVIEW
Designed for portability and ease of use, this reflector features
more than 3 inches of aperture. / / / BY PHIL HARRINGTON
Backpack this scope
These days, telescopes come in a variety
of shapes and sizes. No matter which astronomical niche
you’re interested in, there seems to be a telescope to fit your
needs. That is, except for one. What about a telescope for the
youngest astronomers? Even the smallest refractors and reflectors are usually too large and too heavy for small-fry stargazers
to handle, which means they either have to
rely on an adult to set up the telescope for
them or do without.
To help fill this gap, Celestron recently
introduced the 3.1-inch f/6.9 ExploraScope,
a miniature Newtonian reflector poised on a
unique tabletop base. The ExploraScope
weighs only 5 pounds and measures 14"
long, making it small and light enough for a
7-year-old to carry. The ExploraScope’s
gourd-like shape is reminiscent of Edmund
Scientific’s venerable Astroscan, which can
trace its own roots to amateur telescopes
made more than 30 years ago.
Overview
The ExploraScope’s optics are enclosed
in a white, molded-plastic tube assembly. Two wing-like bulges serve as
grips for either holding or guiding the telescope. A carrying
strap is attached between
the wings. Realizing a
conventional altitude-azimuth or equatorial
mount would be too cumbersome for kids,
Celestron placed the ExploraScope on a
small, concave base. This design lets users
aim the telescope in any direction simply by
pointing. No axes need to be negotiated,
and no screws lock or unlock. Just point the
telescope, and let it go. Users who prefer a
more conventional mount will find an
adapter included for attaching the instrument to a photo tripod. Be sure to check the
adapter connection, as I found it would
work its way loose unless it was tightened
down firmly.
The ExploraScope comes with a 12.5mm
eyepiece already mounted in the telescope’s
cleverly designed helical focuser. The eyepiece threads into a collar that travels up
and down a track inside the drawtube as an
observer turns the black-plastic focusing
ring. The eyepiece magnifies 44x. The
ExploraScope provides a right-side-up view
by employing a built-in lens at the focuser’s
base. Focusing is smooth, without binding
or dead spots.
The ExploraScope is designed to let adult
users collimate both the primary and secondary mirrors. To adjust the primary, pop
off three plastic plugs located at the bottom
of the tube assembly. Inside are three
Phillips screws that adjust the main mirror.
THE EXPLORASCOPE’S FOCUSER is a knurled,
black ring located below the eyepiece. The
front protective cover slides into place easily
and keeps dirt out. ASTRONOMY: WILLIAM ZUBACK
Another trio of Phillips screws allows
adjustment of the secondary mirror, which
is held in the tube by a three-vane spider
mount. The ExploraScope’s instruction
pamphlet includes some rudimentary
instructions on aligning the telescope’s
optics, but if you’re unfamiliar with collimation, seek a helping hand from an experienced amateur astronomer.
Setup’s a snap
The ExploraScope is ready to use right out
of the box — no assembly is required. Just
place the telescope in its base on a picnic
table or other sturdy surface, and it’s set. For
the test, I restricted my explorations to
objects kids would be interested in viewing,
such as the Moon and bright planets.
Initially, I found images were not as crisp
as in some other small, inexpensive telescopes I’ve used. Removing the screw-in
eyepiece and looking into the focuser
revealed both mirrors were slightly out of
collimation. Once they were aligned properly, image sharpness improved somewhat but
still left something to be desired. Part of the
problem lies with the ExploraScope’s inexpensive eyepiece, and the inverter lens in the
base of the focuser may be responsible for
the remaining lack of sharpness.
That leads to one of my disappointments
with the ExploraScope. Although I like the
focuser’s design, it’s just a little too small.
The ExploraScope’s eyepiece looks like it has
a standard 1¼" barrel that’s threaded for filters. But it’s not. It turns out the eyepiece
barrel measures only about 1.2 inches,
which means the focuser’s drawtube is 0.05"
too small to accept 1¼" eyepieces. That’s
really a shame because images could be
improved by substituting even an inexpensive Plössl eyepiece. A 6mm Kellner eyepiece, which yields a magnification of 92x
and which is sized for the ExploraScope, is
available from Celestron dealers for $20.
© 2009 Kalmbach Publishing Co. This material may not be reproduced in any form
without permission from the publisher. www.Astronomy.com
CELESTRON’S EXPLORASCOPE is a great first
telescope for young astronomers.
ASTRONOMY: WILLIAM ZUBACK
www.astronomy.com
93
Life with the ExploraScope improved
after I attached a small, red-dot, singlepower finder to the tube, and I’d recommend anyone buying the telescope do the
same. Keep in mind, however, that because
the tube is tapered, you’ll need to shim the
finder (I used a washer) in order to make it
parallel to the telescope’s optical axis.
You try it
THE EXPLORASCOPE’S TABLETOP BASE is
included and provides a stable platform for
observing. ASTRONOMY: WILLIAM ZUBACK
Under the sky
When I pointed the ExploraScope at the
Moon, I saw a wealth of surface features,
including the central peaks of the craters
Tycho and Copernicus. The Straight Wall
was plainly visible, as were countless small
craters. Of the planets, Venus’ phase was evident, as were Jupiter’s four Galilean moons
and Saturn’s rings. I could make out a hint
of Jupiter’s two equatorial belts, but I couldn’t see the Cassini Division in Saturn’s rings.
I also visited several bright deep-sky
objects. While observing them, I measured
the eyepiece’s true field of view at approximately 0.9°, close to Celestron’s stated value
of 1°. The Pleiades (M45) cluster put on a
nice show. The Orion Nebula (M42)
showed its characteristic shape along with
the four stars of the Trapezium buried
inside. Several bright globular clusters —
M13, M15, and M92 — were apparent,
although the small aperture couldn’t resolve
individual stars. Finally, some well-known
double stars, such as Albireo (Beta [β]
Cygni), were split easily.
Observing quickly revealed the biggest
shortcoming of a scope like this: It’s difficult
to aim. The lack of a finder scope meant I
had to scan back and forth until the target
crossed the field of view. The Moon’s glare
made it easy to acquire, but even Venus,
blazing brilliantly in the morning sky,
took some effort to locate.
A LOOK INTO THE EXPLORASCOPE
reveals a secondary mirror that can
be collimated by adjusting three
screws. ASTRONOMY: WILLIAM ZUBACK
Phil Harrington is the author of the new observing guidebook Star Watch, which is published by
John Wiley & Sons.
94 astronomy /// february 05
Of course, Celestron was not trying to
appeal to me when it introduced the
ExploraScope — the company designed the
telescope for kids. With that in mind, I
loaned the ExploraScope to my brother
Steve and his family. He and his wife, Ann,
have two kids: Lilia, who is 8, and Dan, 4.
None has any working knowledge of telescopes (I just didn’t rub off on Steve during
childhood), which probably makes them
typical of those who will purchase
ExploraScopes. What did they think of it?
After using it during both the day and
night, they came away with a few interesting
points. Lilia especially liked being able to
carry the telescope herself using the shoulder strap, and she thought setup was a snap.
But the simple design of the telescope’s
base also worked against it during use.
Because there is no way to lock it in
place, they found that it was easy to
throw the telescope off its target
when changing observers. Like
many adults who are unfamiliar
with viewing through an eyepiece, the kids grabbed the
scope when viewing. And
unless focusing was done
gently, it threw off the telescope’s aim.
Like me, the family
members
/// PRODUCT SPECIFICATIONS
CELESTRON EXPLORASCOPE
• 3.1-inch (80mm) Newtonian reflector
• 550mm focal length at f/6.9
• 12.5mm eyepiece included
• Carrying strap included
• True field of view: 1°
Length/weight:
14 inches/5 pounds
Street price:
$60 to $70
CONTACT INFORMATION:
Celestron International
2835 Columbia St.
Torrance, CA 90503
[t] 310.328.9560
[w] www.celestron.com
had one problem: aiming the telescope. In
the end, they entertained themselves by
scanning the sky back and forth rather than
selecting targets, save the Moon. Although
there is no suggested minimum age on the
box, I’d surmise the range is 7 to 10.
A few parting remarks
Most results from testing the
ExploraScope were positive.
On one hand, Celestron produced a lightweight telescope
kids can carry and set up on
their own. Images are reasonably sharp and easy to focus.
On the other hand, the telescope
lacks a finder scope and is easily
knocked off target because it’s
held in place by gravity alone.
While the ExploraScope has
some drawbacks, it is still better suited for young astronomers than any
department-store telescope. As
my friend Geoff Gaherty put
it, “many small telescopes
are really toys in disguise,
but Celestron’s ExploraScope is actually a telescope disguised to
look like a toy.” So,
parents, if a small,
portable telescope
is on your child’s
gift list, the
ExploraScope just
might be right for
him or her. X
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