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Go to a star party and what does nearly every scope have hanging from it nowadays? Some form of Digital Setting Circles (DSCs) ! The popularity of these object finding mini-computers has exploded in the past couple of years. The time of Lumicon being the big distributor of DSCs has past and now nearly every large telescope comany caries them. For example, companies the likes of Orion, Meade, Losmandy, SkyComm Engineering, Lumicon, etc. carry such devices.
All display price tags similar to one another, with the exception of Meade, being the lowest (approx. $295). For the most part, though all these companies supply their units for $400+ complete. How does one choose between the many varities? Price and objects in the databases of the respective computers are two main factors. For the latter, most units contain somewhere near 10,000 different objects. These may include, all the Messier, NGC, UGC, and IC objects along with the planets, double stars and room for storage of user-input (asteroids, comets, etc.).
From the above mentioned DSC distributors I choose to purchase my setup from SkyComm Engineering out of Coral Springs, FL. Not only did I compare prices and databases, but I also spoke with users of this particular unit and those with others. The vote was unanimous for the SkyCommander Digital Setting Cirlce unit. A friend of mine, the owner of StarMaster Telescopes, swears by SkyComm and their products.
The installation is quite straight forward and all necessary components are provided in the $438 price tag. Unlike some of the other companies, Victor (owner of SkyComm) provides all mounting brackets for the high-resolution encoders in machined aluminum and brass. Very high quality workmanship! Once installed on your Dobsonian, you will have to make sure your tube can easily pass over top of the azimuth encoder. This was not the case with my 8" Orion Dobsonian; the encoder would prohibit the tube from pointing straight up. If this is the case, you will have to heighten your rocker box. In most cases 3/4" will do the job. If you are still designing your telescope at this time, clearance for the azimuth encoder should be taken into account.
Usage of the computer is also quite simple. The scope is first pointed at two bright stars (two from the 41 or so in the database) and then the date is entered. With those three coordinates the SkyCommander can then find it's way around the sky. If the sky is cut in half, the SkyCommander would tend to be more accurate if you stay in one particular half of the sky. If you venture over to the other half of the sky, accuracy will degrade (slighty, possibly a quarter to half of a degree at times). On cold Autumn and Winter nights, the SkyCommander will require an external battery source to run it's internal heater. Running the SkyCommander without it's heater requires one 9V battery, but the heater requires an extra 3V of power. In this case, it is best to stop by a specialty battery store, Radio Shack or a store that carries alarm systems since they will mostly likely have 12V battery. I use a 12V 7A.H. Lead-Acid battery, which ran me about $35 (the charger was an extra $15). Using both my SkyCommander and cooling fan all night long on observing night (about three or four a month on average) I need only to charge the battery once a month.
I have been using the computer for over two years now and can't complain. I would not have found quite as many deep-space objects as I have without it. Plus Digital Setting circles are great at star parties or when the weather is ice-cold and one would not want to stand and freeze while trying to track an object down.
The decision of choosing a setup is up to the user, but one should definately do research about each of the units (since they are rapidly changing with technology) to get the best deal. Good luck!