NexStar Resource Site

line.gif (861 bytes)
Pop-Up Info Window
(close when finished)
line.gif (861 bytes)

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.

 


line.gif (861 bytes)
Copyright 2000-2017
Michael Swanson
 
  Contact the webmaster:
swanson.michael@usa.net