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Simple-Human

Advantages of Azimuth vs Equatorial vs Dobsonian

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Just wondering what peoples thoughts are on the pro's and con's of the different types of mounts out there? Do Dobsonian mounts have issues on non-flat surfaces (like a garden) or can Equatorial mounts ever have issues getting out of line too easily?

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Dob mount is by far easiest mount to use for heavy scopes, it allows for seated observation (most scopes - depends again on size of the scope). It is very good mount type for visual and very cheap mount type.

There are a few drawbacks - no slow motion controls (but you can actually make them - DIY sort of thing). High power viewing with constant nudging can distract from viewing - there is however option to add EQ platform for tracking (up to 30 minutes and even an hour - but then it needs "rewinding"). You can motorize dob mount but that is not cheap thing to do.

It supports only newtonian type scope (it'll work for some other exotic types - like folded refractor and such - but mostly newtonian/newtonian based like MN and SN scopes) - most other types of scopes have eyepiece at the other end of the tube and that does not work on dob mount.

AltAz mount is very nice mount for visual - can be motorized, keeps eyepiece at the same position for most of the time, can be used while seated down. It has a "blind spot" - it is hard to track object at zenith, and with most scopes it is uncomfortable to view at zenith - eyepiece is at lowest position and requires bend neck to observe.

Principle of operation for these two mount types is basically the same, both are Alt Az mounts and tracking is the same.

EQ mount on the other hand is well suited for astrophotography. It is easier to track with both slow motion controls or with single motor that runs at constant rate (clockwork type motor), but newtonian scopes on EQ mount get eyepiece in weird positions.

It is a bit more time consuming to set up, as you need to do polar alignment, but if you want to have tracking for high power views - it is probably cheapest option (not goto but rather simple tracking motor - it can even be DIY).

Btw, AltAz mount and EQ mount are really different only in EQ wedge that is used to "tilt" mount head and do polar alignment. Some people used EQ mounts in AltAz configuration and some AltAz mounts work in EQ mode by adding polar wedge. There are even models that combine the two out of the box - like SW AZEQ5 and AZEQ6 models.

It really depends on what you want to use mount for and what scope do you plan on putting on it.

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Both mounts have advantages over the other. An altazimuth mount is perhaps more intuitive, as its a simple up/down right/left motion which we all use every day as our heads are essentially Altaz mounted. Altazimuth's are easy to set up and allow the observer to sweep vast areas of sky in autopilot, i.e. with very little thought, and this can be very a very relaxed way of observing. Things become a little more challenging when high powers need to be used, but this generally means just taking more care when altering the position of each axis. They are usually the cheaper option from a beginner's point of view.

Equatorial mounts are less intuitive to use and initially take a little thinking about, but once you've come to terms with the motions, they are equally easy to use. Polar alignment isn't always a critical factor if you're observing at low power, but the advantage of the equatorial is that extreme high powers can be used with very little difficulty once polar aligned. Even at 1000X a target will remain in the field of view if an RA motor is driving the mount. There's something to be said about a tracking mount, as it frees you up for a more relaxed observing experience.  You can sketch an object over an extended period, or even go to the loo or make a brew and get warm for half an hour. On your return to the eyepiece the object is still in the field of view.

Older equatorial mount designs such as the Vixen Super Polaris and Great Polaris, or their Chinese clones, have a manual override ability, so you can disengage the motors or switch them off all together and still guide and drive the mount. You can even sweep the sky using these manual option equatorials by sweeping in right ascension  with a disengaged RA axis. I find guiding the speed of the sweep by holding the counterweight arm makes RA sweeping easy, but I've a short scope which helps. Newtonian reflectors benefit from rotating tube rings as the eyepiece can be kept in a comfortable position, otherwise you can end up in some uncomfortable positions. Refractors are very much at home on an equatorial mount, so scope preference may play a part in deciding which mount works best.

I, like many other observers, use both types of mount but my preference is for the German equatorial mount. My two observing buddies both prefer to use Altazimuth mounts with their refractors. Especially where an equatorial mount can be left set up and permanently polar aligned does it really prove its worth, whether on a permanent garden pier or in an observatory setting. If a scope has to be moved around a lot during an observing session, then the altazimuth pays dividends. 

 

 

Edited by mikeDnight

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Dobs do need a fairly level surface but in practive never seem to have a problem finding a flat enough spot to use it on.. More important is having a dob that moves smoothly and easily. Alt-Az mounts mounted on a tripod have no problems with uneven ground of course. I use both but prefer manual undriven mounts. 

EQ mounts need to be level to operate properly but that’s all part of setting it up before observing.

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There's also the fork mount which pretty much only works for SCTs and Maks (see Meade and Celestron).  The eyepiece can be difficult to get to if it ends up between the forks in a dual fork arrangement.  There are newer single fork designs that would allow you to pivot the diagonal to the side where the missing fork would be.  These single fork mounts tend to be visual only.  Fork designs have the advantage of being lighter than GEMs (German Equatorial Mount, or EQ for short) because there's no counterbalance weights and there's no meridian flip to deal with.  However, they're inappropriate for all but the shortest refractors and Newtonians, so they're limited to use with CATs (Catadioptric or folded designs).  With an equatorial wedge, they can track with a single motor like a GEM.  The newer designs track in alt-az mode with two motors under computer control like any other alt-az mount.

Dobs require fairly level ground, though they will still work pretty well on a gentle slope.  They're really the only solution for 10" and larger Newtonians for most folks.

There's also the split ring mount for Newtonians that have been built by ATMs (Amateur Telescope Makers).  I don't think I've ever seen this design commercialized.  It allows large Newtonians to track in the same manner as they would on a traditional fork mount with an equatorial wedge, but with much more stability.

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