APT Astro's AMF Equatorial Wedge
for the NexStar GPS Model Scopes
14 March 2004
(click this and any other image to view an enlarged version)
Note: as of December 2008 APT's web site is
offline. It appears they have closed their doors
and are no longer manufacturing the wedge. You might find one used or
still in stock at
and astronomy equipment dealer - I would recommend a Google search for "APT
Astro".
Early in 2004, a new astronomy equipment manufacturer caused
quite a stir among NexStar GPS scope owners. APT Astro (www.aptastro.com)
began advertising a line of high-quality accessories designed by
professional engineers. APT boasted not only engineers, but also
complete manufacturing facilities as their parent company manufactures a
wide-range of products.
Their first product to market is the AMF Equatorial Wedge
for NexStar GPS scopes (the latest version is now also compatible with Meade scopes).
It is widely recognized that the Celestron Heavy Duty Wedge is not
sufficiently stable for demanding equatorial work with the NexStar GPS
scopes - particularly the NexStar 11. Other robust wedges are
available, but all are built in low volume, generally one at a time and long
waiting lists exist for prospective buyers. APT on the other hand, has
the manufacturing capabilities to produce as many wedges as necessary to
meet demand. In fact, they intend to ship all orders immediately from
stock.
The question then, is how good is this wedge?
 I received the third wedge built by APT
Astro on March 9th after it traveled several thousand miles from Indiana
to Okinawa, Japan. APT's packaging insured the wedge arrived in
excellent condition. The shipping weight is 46 pounds, and the
wedge weighs nearly 40 pounds, so really, the packing is more important
to help protect anything else in the big brown truck that might be
damaged by the wedge! In concept, a wedge is a deceptively simply
piece of equipment. All we need is a stable tilting platform that is easy
to adjust in both azimuth and tilt (commonly called the latitude adjustment).
Unfortunately, many wedges are neither stable nor easy to adjust. The APT
wedge on the other hand is both and proved an excellent match for my NexStar 11.
 The wedge is truly built like a tank. The tilt plate and bottom
plate are both 1 inch (2.54cm) thick and made of solid aluminum. The
side plates are 3/4 inch (1.9cm) thick and are also solid aluminum. The
side plates are first bolted to the bottom plate and then TIG welded to
insure no possibility that the wedge will rack (twist or rock) side-to-side. This wedge is as
stable as they come. The aluminum is then powder-coated in APT Astro's
distinctive maroon color (other colors are available). Some have mentioned maroon would not have
been their first choice of color, but then, I'm sure many folks were less
than enthused by Celestron's aesthetic taste when they released the now
classic orange-tube C8.
 Adjustments are very easy. With many
wedges, you can make precise adjustments, but when you tighten the locking
bolts, the tilt plate shifts. APT's wedge does not suffer from that
problem at all. Shown here is the azimuth adjustment mechanism.
The outer black ring is mounted to the wedge. The center part of the black
aluminum disk bolts to the top of your tripod or pier and rides in the outer
ring with absolutely no play whatsoever. Turning the large black
handles to either side rotates the inner disk providing azimuth adjustments
up to 10 degrees either direction. This mechanism is so precise,
lock-down bolts are not used and not required - the wedge stays where you
put it.
 The latitude adjustment is also very precise. As seen here, the end of
a threaded rod is attached to a pivoting turnbuckle. The rod moves up
and down through a threaded hole in the pivoting bar attached to the side
plates. The tilt plate is then locked in place by a bolt on each side
of the wedge. Tightening these lock-down bolts does not shift the tilt
plate at all.
Motion of both the azimuth and latitude adjustments is very smooth and
very precise. You will have no trouble at all zeroing in on a good
polar alignment. Coupled with the Wedge Align routine in the NexStar
hand control, you can be up and imaging in very little time. The base plate of the wedge features two eyepiece holes (2" with 1.25"
adapters), a bubble level and a rectangular recess sized specifically for
SBIG camera power supplies. Imagers find the eyepiece holes more
useful to route cables, helping to prevent tangle. The level is a nice
touch as leveling the tripod helps to improve stability by keeping the
 weight directly over the tripod. In addition
to the bubble level and the back of the power supply recess, this picture shows the
center pivot of the base plate as well as the holes the mounting bolts pass
through to attach to the tripod or pier. Attaching the wedge to the tripod
or pier requires a hex wrench of 1/4 inch, but 6mm works in a pinch.
If you are using the stock Celestron Heavy Duty Tripod, there are two ways
to attach the wedge. First, you can use the threaded holes in the top
of the wedge. In this case, your azimuth adjustment range will be
limited. You will only be able to move left or right a couple of
degrees before the adjustment knobs run into the top of the tripod legs.
If you are careful with your initial setup you can make do with this.
This orientation is shown in my final picture below. {UPDATE:
the latest version of the tripod now has a taller base plate allowing the
azimuth knobs to clear the top of the tripod.}
The second method is to use the small threaded inserts that came with the
tripod. {UPDATE: for those who do
not have the inserts, APT has them available for a small cost.} These are placed, from the bottom, into the unthreaded holes
in the top of the tripod - the holes you generally pass the bolts through
when you mount the scope in alt-az mode. In this case, there is no
interference between the tripod legs and azimuth adjuster knobs. Once the wedge is mounted, you face the formidable task of putting the scope
onto the wedge. The larger set of bolts included with the wedge are
for this purpose. Do not try to use the regular mounting bolts, they are
not long enough. These bolts require a 5/16 inch hex wrench, although
an 8mm wrench will generally fit (tightly).
 It is likely you have never
looked at the bottom of your scope. Well, now is the time. You
will quickly notice that there are two sets of threaded holes that the
mounting bolts fit into. The inner set is used when mounting the
scope directly on the tripod in alt-az mode. When mounting the scope
on the wedge, you will be using the outer set indicated by the arrows in
this picture. One thing to keep in mind
throughout this process - do not put any substantial force against the
optical tube while the altitude (declination) clutch is locked.
Over time, this will cause the altitude clutch to loosen and there is no easy
way to adjust it. To protect yourself and the scope, it is best for two people to
work together to mount the scope on the wedge.
Start off by tilting the
scope to the side or setting it overhanging the edge of a table and
threading one of the three bolts into the correct hole. Thread
it in about 2 full turns. Notice that the top bolt hole in the wedge's
tilt plate is actually a slot. Lift the scope onto the tilt plate,
sliding the bolt into the slot. Have your partner help you from the
bottom of the scope base, insuring the bolt slides all the way down into the
slot - with the washers on the bottom of the tilt plate. At this point
you can safely line-up the other two holes and insert the other two bolts.
Tighten all three with a hex wrench. You might also find it useful
that the two threaded holes to the left and right of the altitude adjustment
rod are handy places to hold the two remaining bolts while you are guiding the scope
onto the tilt plate.
 At this point you are ready to use
the Wedge Align routine and the silky smooth adjustments on the wedge to
zero-in on a polar alignment. After everything is set, use that 5/16
inch (or 8mm) hex wrench to tighten the tilt plate lock-down bolts - the one
on either side of the wedge with the large washer.
One last note
about stability. The stock Celestron Heavy Duty Tripod is generally
maligned as being insufficient to support the NexStar 11 on a wedge. I
did not find this to be the case with the APT wedge. I experienced no
quivering at the eyepiece when focusing by hand and even a strong push on
the top of a fork arm produced vibrations that subsided in less than 2
seconds. While this certainly could be improved with a more
substantial tripod, it is acceptable performance. The added weight of the wedge seems to settle
the tripod in a very firm stance. Additionally, the APT wedge is
designed to keep the center of gravity of the scope directly over the top of
the tripod.
So, by now, you know I really like this wedge. I've never seen one
better and most don't even come close. If I had to find anything
negative to say about it, it would be the price. At an
introductory price of $525, it might be a bit more expensive than some are
willing to pay. But, it is certainly worth every penny and I'm betting
it is the last wedge you ever buy for your fork-mounted Celestron scopes.
Visit APT Astro's web site -
www.aptastro.com - for
more details on this and other products. To join in discussions about
APT's products, join the APT Astro Yahoo Group -
groups.yahoo.com/group/APTAstro.
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