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Telescope Mounts

This web page represents the research trail I followed while deciding what telescope to buy. I am new to astronomy and not an expert. Nor do my opinions represent the Memphis Astronomical Society. I just collected all the information I used in considering what kind of telescope mount I wanted and made a web page. I hope this information is useful to other new amateur astronomers. To make the page generally useful I made a list of links for quick reference.

When people think about purchasing a telescope they primary think about optical systems. A very important aspect to using a telescope is the mount. The mount refers to both the legs and the mechanism that holds and points the telescope. The mount is critical for how you use and enjoy your telescope. In the old days mounts were just mechnical devices, but in these modern computerized times, mounts are becoming more intelligent. Mounts have computer guidance systems with built-in astronomical databases. There are many ways to mount and use a telescope, and thus many things to consider when choosing a telescope mount.

Altazimuth Mounts

Between these two motions you can point a telescope to view any position above the horizon. It's a simple system and easy to use and lends itself well to casual stargazing.

Equatorial Mounts

To understand and use the equatorial mount requires a good deal more skill and conceptualization. This knowledge is not required to enjoy using a telescope, or even to use an equatorial telescope because such scopes can be used for casual viewing without mastering all the skills first. The technicque of properly setting up an equatorial mount is called polar alignment. Once configured the equatorial mounted telescope can be aimed with their setting circles using an astronomical coordinate system. Looking at the picture on the right try and imagine these concepts:

• The tripod is positioned so it points along a line with celestrial north. The tripod can be placed pointing anywhere in a 360 degree circle, but you want the front of the mount aiming north. A polar alignment scope helps.
• The first joint above the tripod allows adjusting the telescope to be tilted back the same number of degrees as the viewer's latitude and will bring Polaris, the pole star into view in the polar finder scope. There are different kinds of polar alignment and various methods to perfect it including the drift alignment and iterative method. The goal is to get the scope polar alligned and then locked down for the night.
• The next joint up allows for motion along the right ascension (RA) axis and allows the telescope to follow a star across the sky. If you have ever seen photos of stars making circles in the sky that should help you visualize trying to follow one star as it arcs across the sky. A motor along this axis will track a star. Visualize the celestrial globe turning above, this axis follows the spin of the globe.
• The final joint, the one next to the optical tube assembly (OTA) is call declination and allows the telescope to move up and down the spinning celestrial globe to position the scope at the star's altitude. A motor at this axis helps position the scope.

If you like learning how things work then buying an equatorial scope and using it properly will force you to learn the concepts of celestrial coordinate systems. If you don't care, then consider buying a GOTO scope.

Equatorial telescopes come with setting circles which allow the user to manually position the telescope by using a coordinate system. It's possible to position the scope using the angular markings on the circles, and then track a target by manually turning the RA knob. Motors on one axis or both axis will allow you to observe without readjusting the scope. This is important because as you get into astronomy, the skill of just watching an object is critical to the skill of observing. Looking at one object for longer periods of time will help your eyes adjust and observe more detail. Constant readjusting the view hinders this process.

Accuracy of tracking will depend on the precision of the mount's mechanisms. With decent motors, good gear machining and precise polar alignment, the viewer can watch his target for several minutes or hours without making any adjustments. With fine precision a camera can be used with the telescope.

Which Kind of Mount to Choose?

Aiming the Telescope

Most experienced amateur astronomers recommend that newbies start out with binoculars and learn the sky. That's good advice before buying a telescope and mount. The next piece of advice is to go to some observing events and try out various telescopes. Following these two pieces of advice will help in deciding whether you want to do the driving or leave it to a computer.

Comfort of Viewing

Refractors mounted on tripods can be comfortable to use while sitting in a chair if the object you are viewing is not near the horizon or zenith. If the star you want to watch is at zenith, you will have to get on your knees and even contort yourself to look up sideways. If the object is near the horizon, you will have to stand, bend, or adjust your tripod to sit.

Reflectors which have their eyepieces toward the front of the telescope make looking up easy, as long as the telescope is of similar length to the observer's height. If the scope is huge, an observer will have to use a stool or ladder to view. Smaller scopes require kneeling or bending over to view.

SCTs position the lens at the end of the scope, but because the tubes are short, the eyepieces are generally higher off the ground. Like refractors, the diagonals can be turned to help with viewing.

Stability of Viewing

Heavier telescopes stress the mount, and this is particularly true with equatorial mounts. A keen advantage of dobsonian mounts is their inherent stability.

Stability is of utmost importance when astrophotograhy is being attempted. If you do want to take pictures, either with cameras or CCDs and make long exposures, then prepare to spend a large amount of money for a sturdy stable mount.

Transportability

Some people have a variety of scopes to fit different needs. But if you have just one telescope and you like to use it often, make sure the process of carrying it outside and setting it up won't hinder you from using the telescope.

Manual Target Finding & Tracking

Equatorial telescopes can be crudely pushed and pulled into position, but if they are polar aligned you can use the manual setting circles to position your scope to get into the general area of where you are supposed to look. This takes skill, and it is more mathematical and scientific than just aiming and nudging. Once at object is found, you can use RA knobs to track your target.

You can add motors to both types of mounts and have your telescope automatically follow your target.

Digital setting circles (DSC) allow a computer to help you manually aim your scope. They appeal to the observer who likes to understand the concepts of astronomical coordinate systems, but have the computer do the actual math. Digital setting circles, once configured, give a RA/Dec readout as you move your telescope around. Thus you look up the coordinates of the object you want and push your telescope around till it reaches those coordinates.

Motorized Target Finding & Tracking

Once a GOTO telescope finds your target, it will also track it while you are viewing. So if all you like about astronomy is just the viewing, this type of mount is worth considering.

For astrophotography a GOTO mount combined with an autoguiding CCD camera can be used to achieve extremely precise tracking.

Allignment

Very few amateurs get into astrophotography. It's a very demanding and expensive enterprise. Don't expect your first telescope to need the precision required to take photographs.

Summary

After a year's experience I'm not sure if I would make the same purchasing decision. I think I can safely say that if you are new to astronomy be prepared for one of two things to happen:

1. You will buy a telescope and you won't really use it, or
2. you will get into the hobby and spend a lot of money.
   So the dilemma is: do I buy a little scope to test the waters and then be prepared to buy a bigger one later. Or do I try to buy a big enough scope that will keep my happy for awhile. I went for #2, and I think I should have picked #1 instead. I really should have listened to the advice about binoculars because I'm now having trouble learning the sky. When I started out I wanted high powered views of Jupitor, Saturn and the moon. Now I am wanting wide field views to learn where the stars are. I just spent $250 to get a 2" diagonal and 40mm 2" lens to double my field of view to about 2.5 degrees. But a short tube 80mm will give 3.1 degrees and good binoculars can even double that. The moon and planets will look smaller, but you will see more stars, and thus see the patterns for finding your way around the sky.

   So if I had to do things over again, I would buy some good 7x50 binoculars and maybe the NexStar 80GT GOTO telescope. I am not recommending this telescope, because I've never even seen one. I'm just saying that if I'm going to stick with this hobby it will require learning my way around the sky.

   Use the internet and read reviews and join discussion groups and find out what people think of the mount before you buy your telescope. Beware that everyone has complaints about every product. There appears to be no perfect telescope, so you will need to understand your own habits, likes and dislikes in making your decision.

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