This article is intended to be read after the general introduction to go-to mounts. It uses a specific mount, the DiscMounts DM-6, with an Argo Navis DSC computer, as an example to give a more detailed account of the procedure of setting up and using an alt-az mount with Digital Setting Circles.
We’ll be using a Stellarvue SV-105 refractor and small unit-power finder on the mount for this example.
Various features of digital setting circles are mentioned in the general introduction. On this mount, the specifics are:
Connecting the Argo Navis DSC System
Initializing and Aligning the DSC System
Having set up the mount, it’s time to start the Argo Navis DSC system and give it its first reference — a level OTA.
We set the date and time, and told the Argo Navis that it was being used on an Alt-Az mount, in a previous session, and it remembers that information. Now, we power the unit on and after a few seconds it says
FIX ALT REF
This is the unit asking us to establish its first reference position, the “altitude reference”, which can be a perfectly level or a perfectly vertical optical tube. We press ENTER and it asks which of these options we prefer with a display that reads
The “0°” is the setting for a horizontal tube reference. If we wanted to use a vertical tube, we could rotate the control dial one click and it would read “REF=90°”. We are, however, happy with the horizontal setting requested by the “REF=0°” reading.
We just tilt the telescope forward on the mount until the level is centred, indicating the tube is level. It doesn’t matter which “azimuth” direction (North, East, etc.) the tube is pointing — it only needs to be level.
With the tube level, we press ENTER on the Argo Navis and it responds by saying
WARP=ALT FIX OK
This is the mount acknowledging the first reference position, the “altitude fix”.
Now it’s time to do the 2-star alignment. To pick good alignment stars, let’s have a look at the sky.
At our fairly dark location, looking up, we can see the spectacular spread of stars in the night sky. It’s a little confusing at first.
First Alignment Star
We press EXIT on the Argo Navis to get out to the main menu level, then rotate the control dial until the display reads
MODE ALIGN STAR
Press ENTER to get to the list of suggested alignment stars, and rotate the dial until we see
on the display.
Again, just push gently on the handle of the mount until Arcturus is centred in the eyepiece view. With this system and this telescope, it isn’t necessary to have such precision that a cross-hair eyepiece is necessary, we just centre the star as accurately as we can by eye.
Press ENTER on the Argo Navis, and it replies
WARP= -4.75 (1)
The “WARP” number is meaningless at this point — it is a measure of the distance from where the mount “thought” it was pointed, and it had no idea. It could be any number, and we just ignore it.
Second Alignment Star
Now we spin the Argo Navis control dial until it indicates it is ready for our second chosen alignment star:
We repeat the alignment steps above. First, use the zero-power finder to centre Deneb, just pushing the telescope into position.
We press ENTER and the Argo Navis responds:
WARP= +0.50 (1)
The warp number is now fairly small, indicating that the star wasn’t too far from where the mount calculated it would be. The small error number is due to our centring the two stars only “by eye” and not with a precision reticle. This is good enough. The Argo Navis is now aligned and ready to use, and the whole procedure only took 3 or 4 minutes.
Using the DSC System
Setting up the DM mount and Argo Navis DSC is really simple, and using it is that simple too.
I’m anxious to show you the spectacular globular cluster M13. To get there quickly and easily, back the Argo Navis out to the main menu and rotate the control dial until it says
Press ENTER to enter the catalogue, and rotate the dial to browse the list of available catalogues, stopping when it says
Press ENTER to enter the Messier catalogue, and use the control dial and ENTER key to change one digit at a time, until the display reads
With M13 selected, we press ENTER and see
GUIDE 38 → 40 ↑
(In case the characters don’t render properly on your browser, there are little right-pointing and up-pointing arrows in there.)
The numbers on the GUIDE line tell us which directions we need to move the scope and how far, measured in degrees.
We start gently pushing the scope to the right, watching the display count down:
GUIDE 30 → 40 ↑
GUIDE 22 → 40 ↑
GUIDE 15 → 40 ↑
GUIDE 8 → 40 ↑
GUIDE 4 → 40 ↑
GUIDE 0.6 → 40 ↑
Once the number is close to, or exactly, zero, we adjust the vertical position by pushing the scope upward:
GUIDE 0.6 → 40 ↑
GUIDE 0.6 → 30 ↑
GUIDE 0.6 → 21 ↑
GUIDE 0.6 → 12 ↑
GUIDE 0.6 → 6 ↑
GUIDE 0.6 → 2 ↑
GUIDE 0.6 → 0.5 ↑
Looking in the eyepiece, we find our target.
We can repeat this process all night — go to the catalogue, select an object, and push the telescope until the GUIDE figures are close to zero. Every hour or two it’s worth re-doing the 2-star alignment, or adding one additional alignment star, to compensate for the gradual accumulation of errors in our initial alignment.
Thanks for following along.