Advanced Astromaster Setting Circles

While the analog setting circles on your C-8 can be used to find objects, the convenience of digital setting circles can not be discounted. Having 10,000 objects at your fingertips makes observing more fun! It's much easier to dial in a new object when someone asks "Have you ever seen NGC1514 before" rather than having to pull out your copy of the RNGC or Sky Catalog 2000 to find where this object is.

I added the AAM to my Celestron a couple years ago and have not gone back to the iron circles since then! Here is a compilation of information about the AAM that may help you decide whether you want one and how best to use the unit.

Almost all digital setting circles come from a single company: Tangent. Whether you buy Celestron's unit or JMI's or Orion's, all come from Tangent. The deciding factors in selecting a unit are price, encoder resolution and number of objects in the database. Go with the 4000 pulse encoders and the 10,000 object database and I don't think you will be disappointed. Probably the best reason to buy the Celestron AAM is ease of mounting on your telescope. However, as I learned the hard way - don't count on it!

What exactly are digital setting circles? Here's a brief description for the novice. Digital setting circles are small computer units that keep track of where your telescope is pointed and allows you to position the scope on an object. Optical shaft encoders are secured to your polar and declination axes and the digital outputs from these units are fed to the computer box. The telescope has to go through an initialization routine so that the computer knows where the telescope is pointing. Once this has been established, the computer will keep track of where the telescope is pointing until it is turned off. The early digital setting circles (DSC) were exactly that - all they gave you was the Right Ascension and Declination of your telescope. Later models started to incorporate ROM based data bases that have now grown to 10,000 objects. These include the Messier Catalog, the NGC, parts of the IC and some double stars and other interesting objects. Newer units also include planets and the ability to key in a few objects of your own choosing.

 Here's a picture of the AAM computer and the RA encoder. I have added RJ-11 (telephone) connectors to the cables to make hooking up the device a bit easier and to keep from possibly bending the pins on the encoder units.


Here's the declination encoder mounted on the scope with the protective cover removed.

Again, you will see the RJ-11 connector that was installed to make connection and disconnection easier. Without this connector it is necessary to leave the long cables hooked to the declination encoder or to remove the cover to access the pin jacks and paddle board connection.



This picture shows the declination encoder with the protective cover installed. As you can see, there is no way to remove the cable without removing this cover. Celestron provides 6 self-tapping screws to hold the cover in place. I only use 2 to make removal a bit quicker. Once the encoder is mounted, there should be no reason to remove the cover.

I don't have a picture of the RA encoder mounted on the scope. Here's a shot showing both of the mounting points for this device. The encoder fits into the coupler behind the RA lock. The encoder is secured to a flat bracket about 3 or 4 inches long and this bracket is screwed to the black coupler on the right side of the base assembly. This bracket and the screw keep the encoder body from turning.

Mounting the encoders

Using the AAM

Computer interfacing

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