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Push-to v. go-to

Posted by Darrell Lee   10/31/2004 07:00AM

Push-to v. go-to

I own a Meade LXD55 mount with an 8" Schmidt-Cassegrain scope mounted on it, and a Meade LXD75 mount with a 10" Schmidt-Newtonian. I also own an Orion XT10i Dobsonian with Intelliscope controller. Optically, my scopes are well-matched, with the 10" f/4.7 Dob matching the 10" f/4 SN (with respective focal lengths of 1200 mm and 1016 mm, respectively) for rich field viewing, and the 8" SCT for higher magnification.

My impressions, experience with, and use of these scopes might be useful for astronomers who are thinking of taking the plunge into computer-assisted astronomy, and don?t know whether push-to will be adequate for their needs, or whether they should save enough to buy a go-to scope.

I received the LXD55 mount on the same day as my Intelliscope. I assembled my XT10i and had it finding objects my first night. My LXD55, by comparison, took me weeks of spare time to set up, and months to get it working. The Meade instruction manual was poorly organized and poorly written. It should tell you the necessities of getting the scope up and running (initialize location and scope, calibrate motors, train drives, do a rough polar alignment, and align on some stars), but doesn't. Instead, you have to wade through the entire manual before you get to training drives and doing polar alignments, and the manual doesn?t tell you what?s important to do and what is a waste of time.

With the Intelliscope, you do a vertical alignment, then a two star align until you get a satisfactory warp factor, and start selecting objects. It's a three minute job at most, and I was finding new objects immediately. The Intelliscope display shows you the direction to push your scope, and the numbers in the display drop to 0 when you've hit your target. The target is almost always in your field of view. Not only did I see all the objects I'd laboriously hunted for with my 6" Newt EQ, I was seeing dozens of new objects. Some nights I'd have a list of NGC or Messier numbers, and could easily find a dozen new objects in a night. I've come to love my push-to Dob. Its main disadvantage is no tracking ability. When I'm doing a fine doubles/triple split like Iota Cassiopeiae, the highly magnified image scoots out of the field of view too quickly.

Meanwhile, I'd assembled my LXD55, too. Unfortunately, go-to on an EQ mount is not easy or understandable like push-to. A first-time user has to initialize the controller with the observing site's latitude, longitude, elevation, date, and time. Then he/she has to wade through the owners manual to figure out how to set the scope up to find objects. My first try with go-to, I polar aligned my mount and did a 2 star alignment, but didn?t calibrate motors or train my drives. I should have been worried when the chosen alignment stars weren't in the fov. I told the go-to to find the easily visible moon, and it missed by a couple dozen degrees. Then I told it to point to Albireo, and it failed to put Albireo in the fov. Perhaps I'd been buffaloed by the LXD55 gearheads, who love to hypertune their mounts, or by the other posts from frustrated users who couldn't find objects after polar aligning, drive training, motor calibration, and other complicated setup procedures. I decided I'd do every drive-training and alignment procedure in the manual. That was a big mistake, as I tried to do a Meade-specific instruction with my Orion, confused the Meade saddle with the Orion dovetail plate, and ended up stripping the Dec motor housing screw hole.

I told the good folks at Meade my frustration, and they took mercy on me, repairing the LXD55 mount under warranty even though I'd caused my own problem. By the time I got my LXD55 mount back in mid-August, my new LXD75 had arrived! By then, I was convinced that push-to is all a new astronomer needs, and was phobic about go-to's confusing setup procedures. I was enjoying the view through my 10" Dob intelliscope, and with limited time every night, I used it to stargaze instead of tackling the dreaded go-to setup. I didn't assemble the LXD75 mount or try the LXD55 mount for two more weeks when I had a full free afternoon and evening.

With nothing to lose, I decided to do the absolute minimum go-to setup. I put the SC-8 OTA on the LXD55 mount, initialized the controller, did a rough polar alignment, trained the drives, and did a quick alignment (maybe 45 minutes setup time). I chose a target, and viola! Albireo was in the fov, and it tracked in the fov while I left the scope for several minutes. I quickly called up some familiar Messier objects, and the scope found them all. The advantages of the equatorial mount include image tracking and short-exposure astrophotography, but its main practical use will be in showing objects to friends and family, when its tracking pays off.

Now, with some viewing hours behind me with both systems, I see the benefits of both. Go-to is like a high maintenance spouse or a British sports car, demanding more care to work well, but glamorous and beautiful when it works. Push-to isn't as fancy or glamorous, but gets the job done quickly, steadily, and reliably, without frills. I don't find much difference in pointing/finding accuracy between the two systems. Target objects are in the field of view about 85% of the time, and just outside it the rest of the time. The go-to software claims to contain more than double the celestial objects in its database, but I've yet to see much difference in the push-to and go-to databases. The push-to and go-to controller target menus are fairly similar with menus for Messier objects, NGC objects, planets, monthly sky tours, etc. A quirk of the Intelliscope software is that it doesn't seem capable of finding planets (not even Saturn and Venus, which were bright in the sky). Go-to gave me my first views of Uranus and Neptune.

There's a big price difference to consider. Push-to costs roughly half the price of go-to for the same telescope aperture. The Intelliscope uses a 9v battery and will easily run for a week of observing sessions on a single battery. The motorized go-to mount requires a rechargeable 12v motorcycle battery at minimum, since eight D cell batteries will cost you as much as a motorcycle battery, and either will barely last you for a full night of viewing.

To underscore that high maintenance difference, my new LXD75 mount went back to the factory for warranty repair. Its first time out of the box, during first alignment, the RA gear slipped. The motor whirred, but the scope didn't move.

I think most people will be very satisfied with push-to technology. It does the job at the best price. I find that any time my viewing time is limited, I pull out my push-to scope. Go-to is best suited for budding astrophotographers and people who study the same objects for hours.

Darrell Lee
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