I've had my ETX 125 for a few days now, and have been playing with the Autostar for quite a while. I thought you might be interested in what I found.
Autostar Tips & Alignment
A great deal has been written about the difficulties of using the Autostar controller. I've read a lot of this advice and tried a couple of things when I got my scope. The result was that I had no trouble using the Autostar. In all my observing sessions, the Autostar puts all objects very close to the center of the 26 mm eyepiece of my ETX 125.
The Home Position
Meade makes great telescopes, but they write lousy manuals. I had a couple of questions about aligment, and even their Tech Support had a hard time giving me answers. So here's how I align the telescope for the home position.
First, I always use the scope in Alt-Az mode. There is no advantage in using Polar mode, unless you plan to take long-exposure images with the scope--a real challenge with the ETX.
An important point in which I differ from others is that I DO NOT level the platorm or mount on which my scope sits. My driveway has quite a slope from west to east, but I do not compensate for this by leveling the mount.
First, I point the scope roughly north, with the control panel on the scope base pointing west, and then rotate the OTA anti-clockwise until the RA axis hits the hard stop. Despite what the Meade docs say, the arm with the declination lock on it will NOT be over the control panel--it will be a little in front of (to the north of) it. I then turn the OTA clockwise on the base until the arm with the declination circle is over the control panel. This clockwise turn is about 180 degrees. I then lock the RA axis.
To finish the job, I align on Polaris. I move the whole base of the scope (with the RA axis locked) until it points to the approximate direction of Polaris. I then move the scope in decination until Polaris is in the finder scope. I lock the Declination axis and use the hand controller (in declination ONLY) to put Polaris as close to the center of the eyepiece field as I can. All RA adjustments are achieved by moving the whole base of the scope in RA (with the axis locked). If you're using a tripod, you'll need to move the whole assembly. When Polaris is centered, I use the Autostar to move the scope in declination only. As the scope approaches the horizontal, I place a small spirit level on the tube. The level is parallel to the optical axis (i.e. facing the way the tube is pointing).. I stop moving the scope when the spirit level tells me the OTA is level. The ETX is now in the Alt-Az Home position.
Training the Drives
My observing site is an astronomer's nightmare. It is surrounded by tall trees and altogether quite wooded. Meade recommends training the drives using a terrestrial object because, of course, celestial objects move as the earth rotates. My problem was that I could not find a terrestrial object far enough away to train the drives effectively. However, Polaris moves very little in the sky as the earth rotates, and so I used it to train my ETX drives.
To train the drives, I first put my scope in the Alt-Az Home position--again, without leveling the mount, just making sure the OTA was level in the direction in which it was pointed. I then centered Polaris in the field and trained the drives.
The advantage of using a point source is obvious--you can tell exactly when the object is centered in the field of view--something that is harder to do if you use terrestrial objects. The result is that your drives can be trained very precisely with this method, even if you use only the 26mm eyepiece.
After training, two star alignment puts alignment stars in the field of the finder scope (usually toward the edge). After aligning on both stars, Autostar is extremely accurate. Most of the objects I GOTO are very close to the center of the field of the 26mm eyepiece, even if I'm slewing halfway across the sky.
Subject: Drive Training Tip Sent: Friday, February 16, 2001 14:45:59 From: email@example.com (Clay Sherrod) I think training the telescope at or near 45 degrees is one of the easiest and most beneficial things that any ETX owner can do to increase the accuracy of his or her telescope. Although my latitude is about 35 degrees, that is still high enough for me to train on Polaris instead of a land-based object, putting just enough load on the OTA to make it work in training the motors. clay -----Original Message----- From: Autostar Software Review Project (firstname.lastname@example.org) >Clarifying (I hope) my earlier comments, I *think* I've reduced >snap-back slewing. But that's based on a very brief (5 min?) peek at >the Sun on Thursday followed by looking around my neighborhood with >the OTA raised somewhat but nowhere near what happens when doing sky >gazing. I suspect the scope actively moved down in elevation after I >tried centering the Sun in my 26 mm EP by tilting up and this happened >more than once. OTOH, I've seen far worse amounts of motion with the >same EP so *maybe* the problem is reduced. The forecast for the >weekend looks promising for at least clear skies if not good seeing. >I'll update the situation as appropriate. > >As to what I did, the only change was to try training the scope at 45 >deg. elevation. Because there aren't a lot of obliging fixed targets >at the elevation, I had to make do with a telephone line running >diagonally acoss the FOV. > >Cheers, > Rick
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