S & T Test Report
Rod Mollise
Celestron Package:
A Lot
for a Little
An ensemble of Celestron equipment provides excellent visual and
photographic performance.
As robert heinlein
used to say. “There
ain’t no such thing as a free lunch.” That’s usually true,
but I almost feel like I got a free meal with Celestron’s
Edge 800 Schmidt-Cassegrain Telescope and VX mount.
I found the combination of the advanced 8-inch SCT and
inexpensive German equatorial mount (GEM) surprisingly capable, especially when equipped with Celestron’s
Edge f/7 reducer, off-axis guider, and StarSense autoalignment system.
I have dreamed of an enormous SCT on a fork mount
to ease me into my golden years. Unfortunately, I have
to carry my scope to dark sites to do my best observing,
and I really didn’t want to haul a 14- or 16-inch telescope
around. The more I thought about it, the more convinced
I became that an 8-inch SCT was still the scope for me.
Maybe my retirement scope should be a C8 of a new type,
though, Celestron’s Edge 800.
VX MOUNT U.S. price: $1,799
Excellent Go To accuracy
Tracking good enough for unguided 30-second exposures
Stable with an 8-inch SCT and accessories
Hand-control cable is too short
The included counterweight is too light for use with the
telescope and heavy cameras or accessories
The author’s Celestron 8-inch Edge SCT sits atop a VX German
equatorial mount. The standard 9x50-mm finderscope is attached.
A 12-pound counterweight is included in the package.
December 2014 sky & telescope
Different from other Schmidt-Cassegrains, the Edge
includes a built-in corrector-lens system that both flattens
the SCT’s normally curved field and reduces coma, the
blurring of stars at the field edge. For more on the Edge,
see Dennis di Cicco’s review of the Edge 1400 (S&T: Feb.
2011, p. 52). The Edge 800 is a scaled-down version of its
innovative big sister.
I thought I’d purchase a new mount too — one that
Celestron is pairing with the Edge 800, the Advanced VX.
The VX’s payload capacity is 30 pounds (14 kg), making
it the company’s smallest computer-equipped GEM. But
it’s well matched for a C8. Celestron currently offers the
combination as a package for $1,799.
I purchased the telescope and mount last year,
and they arrived in pristine condition. The tube came
equipped with a 50-mm finder and a Vixen-format dovetail bar to fit the VX. S&T recently borrowed a StarSense
and an off-axis guider from Celestron and shipped them
to me to complete the package so I could write this review.
The box that contained the VX mount included the
GEM head, a 2-inch steel-legged tripod, a single 12-pound
counterweight, the NexStar Plus computer hand control,
a cable for updating the mount’s firmware, an instruction
manual, the basic version of Software Bisque’s TheSkyX
planetarium software, and a DC power cord with a
cigarette-lighter-style plug.
The Edge 800 is a striking pale green and the mount is
impressively well finished for a GEM in this price class. I
particularly appreciated the VX’s large adjustment knobs,
well-laid-out control panel, and big power switch that’s
easy to manipulate with gloved hands.
Visual Use
On my first clear night, I hustled the new scope out to my
club’s dark site. I didn’t run into any problems assembling
the mount or attaching it to the scope. After a little practice, most people won’t need more than 10 to 15 minutes
to set up the Edge/VX combo for visual use.
The big deal, though, was not how easy the scope
and mount were to assemble, but how easy they were to
transport. The package breaks down into easily manageable components that encourage me to use it frequently.
At 14 pounds (6.4 kg) for the telescope, 17 pounds for the
mount head, and 18 pounds for the tripod, I never had to
strain. The telescope was quite stable on the mount with
vibrations dying out in a couple of seconds.
A GEM must be property aligned on the celestial
pole to track stars accurately. Polar alignment is simple
for visual use. Remove the end caps from the VX’s right
ascension housing, turn the scope perpendicular to the
mount’s head to open up a hole in the declination axis,
and then sight Polaris through the hollow polar bore.
After these steps, the mount’s Go To system will fi nd
objects with even the roughest polar alignment, though
tracking will be poor.
A DSLR is attached to the Celestron off-axis guider. The autoguider camera is not part of the reviewed Celestron package.
Before the VX can locate objects, it must be Go To
aligned. The first step is entering the time, date, time
zone, daylight-savings time status, and location into the
hand control. Most of these entries will be a one-time job
because the mount is equipped with a battery-powered,
real-time clock that keeps the date and time current.
There are several alignment options, but the most
accurate is the two-star alignment. When you select that
option, the VX will point at two stars it chooses from its
database. After you center them in the finder and main
scope, the hand control will ask if you want to add calibration stars. You may add as many as four, but I found three
sufficient for excellent pointing accuracy.
Even at a magnification of 100×, anything I requested
from horizon to horizon was in the eyepiece when the
mount stopped. In the year that I’ve had the VX, it amazingly has never missed an object when I’ve been careful
to do the alignment as outlined in the manual. The only
problem I have encountered has been the 3-foot-long
hand-control cable, which is a bit short.
The Edge f/7 Reducer
The addition of Celestron’s Edge focal reducer converts
the f/10, 2,000-mm-focal-length Edge 800 to an f/7,
1,400-mm-focal-length telescope that delivers lower powers and wider fields of view. The reducer is specifically
designed to work with the Edge’s built-in corrective lenses
to preserve the scope’s flat field. Although intended for
astrophotography, I found the reducer very effective for
visual use as well.
EDGE FOCAL REDUCER U.S. price: $299.95
Sharp stars to the field edge
Using larger imaging chips could pose a problem
Sk yandTelescope.com December 2014
S&T Test Report
For prime-focus deep-sky imaging, a focal reducer is
highly desirable. The Edge reducer, which is optimized for
small imaging chips, almost doubles the size of a telescope’s field and cuts required exposure times in half. With
my Canon DSLR, stars were sharp all across the frame.
Unguided Imaging
Since astrophotography was in my plan on a trip to the
Chiefland Astronomy Village in Florida, I kept things
simple. I shot through the SCT and reducer with my
DSLR, but I didn’t guide any exposures.
I mounted my Canon 60D camera to the scope with
a standard prime-focus adapter threaded onto the Edge
Reducer, which replicates the normal SCT threads. The
only problem I ran into was balance. The VX’s single counterweight was not heavy enough to balance the telescope
in right ascension with the camera onboard. Fortunately, I
had brought an additional 11-pound counterweight.
Because good tracking is critical for imaging, once
the Go To alignment was complete, I performed the VX’s
All-Star Polar Alignment procedure. After centering a star
I chose from the hand control’s database, I completed the
process by re-centering it again using the mount’s alti68
December 2014 sky & telescope
The author imaged the Dumbbell Nebula (M27) through the Edge
800 setup. The picture is a stack of twenty 30-second unguided,
prime-focus exposures using the Edge f/7 focal-length reducer.
tude and azimuth adjusters rather than the hand control.
Preliminaries over, I sent the scope to M15 and began
firing 30-second exposures. I shot twenty 30-second
subframes of the globular. My stars were not quite round
in all frames, but stacking these short exposures into a
finished picture yielded pleasing images. What’s amazing
is that a beginner could have achieved similar results. I
didn’t do anything special; I just snapped away.
The Off-Axis Guider
If you want to go much beyond 30-second exposures,
you’ll need to guide the VX. Today, that’s done with an
autoguider camera that plugs into the VX’s autoguide
port. You could use a separate small telescope to provide
guide stars for the camera to monitor, but flexure between
the main scope and guide scope can cause trailed stars.
Enter the Celestron off-axis guider (OAG).
When I opened the box containing the guider, my
heart sank. There appeared to be a million adapter rings
OFF-AXIS GUIDER U.S. price: $249.95
Good construction quality with large, clear aperture
Camera and T-ring attach to off-axis guider with less-thansecure setscrews
and spacers. Luckily, the instructions for configuring the
OAG for my setup were clear. Three setscrews attached the
camera to the guider body. I prefer a more secure connection, but it caused no problems and I was impressed by the
OAG’s otherwise hefty construction and quality finish.
My pictures with the guider weren’t award winners
because I was imaging from my light-polluted backyard
under a full Moon. And I did have one scare — when I
began autoguiding at first, the guide camera didn’t pick
up a single star. It turned out that my autoguider wouldn’t
reach focus without an extension tube due to the presence
of the Edge reducer. With the guider inserted into the
tube from an old Barlow, the OAG worked well, keeping
stars respectably round.
The StarSense AutoAlign Camera
Celestron’s StarSense accessory mounts to the Edge’s tube
in place of the telescope’s 50-mm finder and automates
the Go To alignment process. The box contained a small
Completes a good Go To alignment in 3 minutes
The All-Star polar-alignment feature did not function
The Celestron StarSense camera takes the place of the standard 9x50-mm finder when used. This camera automates the
Go To alignment process.
The author’s image of globular cluster M15 consists of twenty
30-second, stacked, unguided, prime-focus f/7 exposures.
camera and a replacement NexStar hand control. Connect
the StarSense controller in place of the original, hook the
camera to one of the mount’s Auxiliary ports, and you’re
ready to go.
I was skeptical that such a seemingly simple gadget
would enable the VX to align itself. Nevertheless, it
worked. I turned on the mount, entered the date, time,
and city, and selected Auto Alignment. StarSense directed
the mount to take images of star fields on both sides of
the meridian. Despite a bright Moon, the camera was
sensitive enough to acquire 40 to 100 stars every time. In
only three minutes the StarSense indicated that the VX
was aligned. We’d see about that.
I punched in M13. There it was near the center of the
field of a 20-mm eyepiece at 100×. M57? Same. M3? Yep.
Every single object from horizon to horizon was in the
eyepiece. Go To accuracy seemed just as good as with
alignments done the old-fashioned way.
Not that the StarSense was perfect. My eyes had difficulty with the display’s small fonts. More significantly,
the StarSense’s All-Star polar-alignment routine didn’t
work. The results it yielded were inaccurate — it put the
telescope degrees away from the celestial pole. I contacted
Celestron technical support, who assured me they are
working to make All-Star functional by the end of 2014.
Even without All-Star, however, the StarSense was amazing. Not only did it align the VX as well as I could, it was
just so cool.
The VX mount is not a caviar-class GEM, but it makes
up for that with its low price, portability, and solid performance. Throw in the optically impressive Edge 800,
the Edge Reducer, the off-axis guider, and the StarSense,
and a novice — or an old hand — will be equipped with a
system ready to take on almost any task for a price lower
than I would have thought possible. ✦
S&T contributing editor Rod Mollise writes an entertaining
astronomical blog at www.uncle-rods.blogspot.com.
Sk yandTelescope.com December 2014