[Return to the DDU FAQ Index]
[Back to Section 3: Collimation] [Proceed
to Section 5: Other Questions]
4.1) What are Digital Setting Circles, or DSCs?
4.2) Should I consider buying DSCs?
4.3) Are there any reviews of the Discovery DSC kit?
4.4) Is the Discovery DSC kit my only option?
4.5) My DSCs don't seem to be working correctly...
4.1) What are Digital Setting Circles, or DSCs?
P.J. Ward's site on the Barden Ridge Observatory defines digital setting circles thusly:
Digital setting circles (DSC's) come in a variety of shapes sizes and capabilities. Their most basic function is to accurately display the coordinates in the sky to which a telescope is being pointed. More advanced units have built in object catalogues or databases which can be quickly accessed to point a telescope to any one of these objects. Even more advanced units have a built in computer port (RS232) which can repeat the position of the telescope to a planetarium program, which then displays a cursor on a star-chart, again indication the telescope's current pointing.
Before you do anything else, read the DSC FAQ section of the Purchasing Amateur Telescopes FAQ, written by Jim van Nuland. This tells you a lot!
Tom Truscock has also written an exellent DSC primer on Cloudy Nights
4.2) Should I consider buying DSCs?
NO!!! Okay, now you know my opinion, but read on. :)--Wes Stone
The answer really depends on a lot of things
- Cost. At around $500, they're not cheap.
- Observing style. Some people (like Paul Markov and Art Russell get their kicks starhopping. DSC detractors say (among themselves, and over beer) that DSCs are a hop, skip and a jump away from those infernal "goto" scopes, which do everything for you, include grind the coffee (which, rather than a bug, might be a feature!). DSC enthusiasts counter by saying that DSCs are, much like sky atlases and laptops, another tool in the amateur's arsenal to be used whenever the observer deems it necessary. Each of us knows what's fun for ourselves, and where we get our kicks.
- Conditions. DSCs are useful for observing dim objects among dim stars. In such conditions, starhopping can be be a serious problem. I disagree here. Just to see a really, really dim object requires an intimate knowledge of a starfield that you'll get from starhopping via a very deep chart and/or image. It's not enough to have the object's putative coordinates near the center of the field. Maybe DSCs will help you locate "bright to moderately dim" objects without an adequate chart. --Wes Stone
- Surveys. DSCs are useful for quickly locating a series of objects quickly, or without much downtime between views (such as at a public star party).
4.3) Are there any reviews of the Discovery DSC kit?
Not entire articles, but a few people have weighed in on the topic:
[Don D'Egidio] I have Discovery's DSC kit for my 17.5" TD and they are well thought out with only a minor complaint. The azimuth encoder is attached with a new bolt and center pivot that accepts the encoder shaft and is held with a setscrew. My only complaint is that I wish it was about 1/4" higher and used a thumbscrew instead which would make removing the encoder when needed easier. As it is now you would need to remove the entire center bolt and pivot then loosen the setscrew and remove the encoder.
[Penny Fischer-Otte] Well, I am pretty impressed with the DSC's from Discovery. The install was not too bad, taking about 40 minutes, some of the original components of the Dob base are no longer used such as some Teflon pieces and the center bolt. The finished assembly was nice and neat, in fact, better than a lot of other DSCs I have seen, more professional looking and seamless. The set up was a bit of a pain... it took a while because we did not find the instructions explicit enough. But the operation of the DSC's is WAY easy and we can knock out 20 objects in the time it takes to find two or three manually. I would recommend their product.
4.4) Is the Discovery DSC kit my only option?
A few people have assembled their own kits, but more people on the list seem to have bought the Discovery DSCs. There are, in fact, two major manufacturers of DSC computers: Sky Commander and NGC-MAX. Discovery uses the latter. Jeff Lipsman wrote a DSC computer comparison that you might want to read. Newer on the block is the Argo Navis, reviewed on Cloudy Nights by Tom Trusock
Dave Grimmer posted an excellent summary of his experience using the Sky Commander product with his 17.5 Truss Tube. He recently gave an update, 6 months later:
[Dave Grimmer] I ordered the encoders, mounting hardware and cables from Discovery with my scope, and placed an order with Sky Engineering for their Sky Commander product. I have had zero problems with it. The tool has allowed me to spend more time looking at objects and less time looking for them. I have been star hopping with an 8" Dob for the past 15 years, so I've learned the sky pretty well. I can see to about mag 4.5 from my driveway, so the DSC really helps when there are few guide stars to "hop" with.
For those who want a GOTO option, the ServoCat Jr. and related products are available.
4.5) My DSCs don't seem to be working correctly...
There are many possible problems. Here's some advice from the list:
[Fred Kiesche] A good initial alignment of the scope with the first two stars helps. This should lower your warp factor. And, to keep things going, you need to realign every now and again. What I do is to realign on every "point object" that I observe. So, when I observe a double star, I press the realign button. Ditto Planetary Nebula, etc. I consistently get the warp factor down to 0.0. It'll start to creep up again, especially if you observe "non-point" objects (galaxies, nebula), but you can keep it low by using realignments.
[Return to the DDU FAQ Index]
[Back to Section 3: Collimation] [Proceed
to Section 5: Other Questions]