Losmandy Schwab.qxd:Layout 1

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The
Losmandy
GM-8
A Solid, User Friendly
Equatorial Mount
By Don Schwab
I have used a variety of designs of
German Equatorial Mounts (GEMs) from
different makers and my biggest problem
has always been frustration with fiddling
with the right ascension and declination
locking levers in the dark. With most designs, to slew the scope by hand, we must
first unlock both axes of rotation, reposition
the scope, and then relock both axes to hold
the position and allow proper tracking. For
me, this can be a real pain-in-theneck...literally!
Of course, if you’re using automated goto controls, you don’t necessarily have to
lock and unlock the axes – just perform the
required alignment procedures, push a few
buttons on a hand controller, and the electronics will take you to your selected astronomical object.
But I’m not a go-to guy. So, I started
searching for a noncomputerized mount
that would require the
least amount of manual dexterity to navigate the heavens. I also
wanted an equatorial
mount that was capable of handling the
load of a mid-sized refractor (4 inches) together with a DSLR
camera for imaging.
Because of the additional demands of as- Image 1. The large knurled declination clutch knob is located
trophotography and where the substantial counterweight shaft meets the declination
keeping in mind the housing.
weight capacity guidetwice the load of the scope and imaging
lines recommended by many experts, I
components that I anticipated placing on it.
searched for a mount that was rated to carry
My intention was to permanently
Astronomy TECHNOLOGY TODAY
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THE LOSMANDY GM-8
Image 2. This view of the Right Ascension clutch knob shows the spring washer that
maintains the clutch load set with the knob.
locate the mount, scope and related imaging gear in my garage rooftop observatory.
Because of vibrations I create when in the
small observatory room and garage, I
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Astronomy TECHNOLOGY TODAY
wanted to be able to center the target, focus,
set the auto-exposure timer, and make a
quick exit completely away from the garage,
leaving the undisturbed mount to track, un-
guided, while the camera snaps relatively
short exposures. While waiting for completion of the imaging routine, I could be in
the yard with the grab-n-go setup I use for
visual work.
After researching all alternatives, the
specifications of the Losmandy GM-8 impressed me and, after checking out what a
number of GM-8 users had to say online, I
placed my order with an authorized Losmandy dealer. The price was higher than
most other brands claiming a 30-pound or
greater weight capacity, but I really liked the
fact that the GM-8 features adjustable slipclutches rather than the more common axis
locks. I was also very impressed with the
quality of the machining of the GM-8’s aluminum and stainless steel components, as
well as the overall fit and finish of the assembled mount.
The Losmandy GM-8 has proven to be
an excellent mount for my application. The
slip clutches are a real plus - no more grasping blindly for knobs in the dark and repeated unlocking and locking of the axes. If
THE LOSMANDY GM-8
Image 3. The tiltable drive corrector provides 6 slew rates: 0.3x and 0.5x for guiding and
2x, 4x, 8x and 16x for faster slewing. There are 4 tracking drive rates: Sidereal, King,
Solar, and Lunar. The corrector also features PEC, TVC, and provision for operation in
both Northern and Southern hemispheres.
Image 4. The compact hand controller features an intuitive “diamond” push button
pattern.
the tension needs to be adjusted on the
clutches, the large knurled knobs (shown in
Images 1 and 2) are easy enough to find,
grip and adjust in the dark, even with gloved
hands.
The tripod is very stout as delivered, but
I have added a homemade, hardwood accessory tray for convenience and even greater
stability. I’ve also fixed each tripod leg to the
floor of my 6-foot by 6-foot observatory
space. With such tight quarters, I wanted to
make sure that bumping a tripod leg would
not mess up my alignment and this has
proved to be a wise precaution – I have the
bruises on my legs to prove it!
With the adjustable height tripod, laserengraved
latitude
scale,
built-in
tripod level, and user-friendly azimuth and
altitude adjustments, polar and drift alignment is a breeze! As mentioned earlier, I do
not use auto-guiding and I find that the
GM8 does a superb job of tracking, even
without such assistance. With my 10-pound
refractor, finder, counterweights, and camera
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THE LOSMANDY GM-8
Image 5. The declination analog setting circle is laser engraved in increments of 2 degrees.
riding on the capable mount, I’m able to
capture very decent images by taking relatively short exposures.
My exposures are normally 120 to 180
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Astronomy TECHNOLOGY TODAY
seconds and 95 percent (approximately 19
out of 20) of the raw images that I capture
show no signs of tracking errors. The mount
has provision for a Periodic Error Correction
(PEC) routine, but I find it too time consuming to bother with, given the success I’ve
had without it. Because PEC isn’t stored between sessions, it has to be reset for each new
session and I simply see no reason to invest
that additional time and effort.
The GM-8 also has provision for Time
Variable Compensation (TVC), a function
that may be useful for some, but again, I
choose not to use it because of the time involved. TVC is designed to minimize backlash in the declination motor, but, like the
PEC function, has to be reset each time you
power up the drive. Here in Northern
Michigan, clear skies are rare. So, when the
opportunity for observing and imaging
does present itself, I want to spend my time
doing just that rather than PECing and
TVCing. For those whose astrophotography requirements are more strenuous than
mine, I’m sure that both functions would
be very helpful and well worth the time
and effort.
The build quality of the GM-8 is “top
notch” and the drive corrector features four
basic quartz tracking rates: Sidereal, King
(a modified sidereal rate), Solar, and Lunar.
Among the other user friendly features of
the tiltable control panel (Image 3) is a
dimmer button to adjust the intensity the
red LED control lights, or to turn them off
completely, which is very useful for preserving night vision.
Image 4 shows the compact handcontrol box. It fits my hand comfortably
and has a nice slewing feature that I find
very useful – while pushing a directional
arrow button to move an object in right ascension or declination, you can temporarily
increase the speed to 16x by simultaneously
pressing a corresponding button. This does
not permanently change the tracking speed
– once the buttons are released, the 12-volt
DC stepper motors automatically resume
the correct tracking rate.
Even though there is a $1,000 option
for adding the go-to Gemini system to the
GM-8, I chose to stick with the manual
route. It seems that the majority of telescope users prefer go-to systems and, I sup-
THE LOSMANDY GM-8
pose, that’s the reason that many small to
mid-size GEMs are only equipped with
small, hard-to-read setting circles. The Losmandy GM-8 features 3.5-inch diameter
setting circles (Images 5 and 6) that are actually quite functional. The GM-8’s analog
circles are laser engraved for both Northern and Southern hemispheres, of adequate
size, and accurate enough to routinely get
me within finder or low power eyepiece
range of those elusive DSOs. The Right
Ascension circle is marked in increments of
6 minutes, while the Declination circle is
marked in increments of 2 degrees.
Now I certainly don’t claim to be an
expert at astrophotography – far from
it – but the GM-8 and my simple gear
have allowed me to have great fun and to
capture images of God’s universe that I feel
are worthy of sharing with family and
friends. Images 7 and 8 are “fun”images
that demonstrate the unguided tracking
accuracy of the Losmandy GM-8. Image
7 is an unguided, 3-minute exposure of
M27, the Dumbell Nebula, and Image 8 is
a “stack” of unguided, 2-minute exposures
of M51, the Whirlpool Galaxy.
In the time that I have owned the
GM-8, I’ve done nothing to modify or improve the gears – I'm happy with the way
the standard configuration performs and
firmly believe in the old adage, “If it ain’t
broke…don’t fix it!”
In my opinion, the fine craftsmanship
and tracking accuracy of the Losmandy
GM-8 make it a very attractive choice for
anyone wanting a German Equatorial
Image 6. The easy to read and very functional Right Ascension setting circle is laser engraved
in increments of 6 minutes.
Mount for user-friendly visual observing,
or for astrophotography work. In the latter
role, it is fully capable of carrying the more
than 15 pounds of telescope and related
imaging gear plus counterweights that I
load mine with.
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Astronomy TECHNOLOGY TODAY
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THE LOSMANDY GM-8
Image 7. This unguided, 3-minute exposure of M27 was captured with the author’s 4-inch refractor and DSLR using the GM-8.
FEATURES AND SPECIFICATIONS
Equatorial Head
• All machined components of
stainless steel or black anodized
aluminum
• All stainless steel hardware
• One 2.10-inch diameter needle
thrust bearing
• One 2.00-inch diameter needle
thrust bearing
• Two 1.50-inch diameter needle
bearings
• 2.812-inch diameter, 7075
aluminum worm gear, 180 teeth
• Dual supported, ball bearing
housed stainless steel worm, heat
treated and ground
• Variable slip clutch on both axes,
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Astronomy TECHNOLOGY TODAY
each with single-knob adjustment
• 1.25-inch diameter aluminum
shafts
• Fully locking, tangent-arm design
altitude adjustment from 0-64
degrees with large knob for easy
alignment
• Laser engraved latitude scale in
2-degree increments
• Single knob azimuth control,
bi-directional +/- 8.5 degrees
• 3.50-inch diameter laser engraved
setting circles with 6-minute R.A. /
2-degree DEC engravings. R.A.
circle engraved for both Northern
and Southern Hemispheres.
• Porter slip ring design.
• 160 ounce/inch stepper motor, 1.0
arc-second step
• Spit Dovetail saddle-plate design.
Accepts Losmandy “D” series
dovetail plates.
• Removable stainless steel weight
shaft w/safety knob
• 7-pound counterweight included,
11-pound and 21-pound extra
counterweights available
• Through-the-axis polar scope,
works in Northern and Southern
hemisphere. Polar scope optional
• Instrument weight capacity:
30 pounds
• Equatorial head weight: 21 pounds
THE LOSMANDY GM-8
Image 8. A “stack” of unguided, 2-minute exposures of M51.
Dual-Axis Controls
• Diamond push button pattern
hand control with R.A and DEC re
versing switches
• Three guiding rates: 30%, 50%
and 2x sidereal rate
• Three slew rates: 4x, 8x, 16x
sidereal rate, plus super fast 32x
HST (high speed transfer)
• Quartz tracking rates: sidereal,
solar, lunar, king
• Periodic Error Correction (PEC)
• Programmable DEC. Backlash
Compensation (TVC)
• Control panel dimmer
• Accepts auto-guider systems
• Northern and Southern
Hemisphere operation
• 12 volt DC, 500ma power use
• Tiltable control panel for easy
access
• Small hand control box for
comfortable use
Tripod
• Constructed of black-anodized,
machined aluminum
• Tripod height adjustable from 27
to 43 inches
• Fold-up tripod design for easy
transport
• Weight: 15 pounds
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