July 27, 2018: Goto Telescopes / Mounts

So, let’s say you bought your first scope for around $150 to $300 – maybe it’s the Astronomers Without Borders One Sky scope, or one of its clones, like the Meade Lightbridge 130.  Perhaps you’ve bought a refractor, like the Meade Infinity 102.  Or, it could be that you bought something like the Celestron Astromaster 130 (which I don’t recommend, but, hey, you be you).  And now you want to get something a bit better, a bit easier to use, . . . maybe a bit larger.

Well, one way to go would be to just get a dob.  An 8-inch dob would be a great upgrade over a 4 or 5-inch scope.  It’s easy to use, still relatively portable, and it lets you go significantly deeper because of the increased aperture.  An 8-inch dob is right at that sweet spot of significant aperture and portability.

But what if you’ve done the whole starhopping thing, and you’re just not interested in finding stuff on your own anymore?  Or, maybe you’re looking for your first scope and you just have no interest in locating the stuff yourself?

Enter the goto scope.  At the suggestion of one of my nine loyal readers, let’s take a look at what they are, what they do.

A Brief Starhopping Rant

Before we goto there (ahem), let’s talk a little about starhopping.  The obvious thing that a goto scope lets you do is to view objects without having to know their location in the sky, without having to learn how to read a star atlas and starhop.  Whenever a beginner asks the eternal question, “What scope should I buy?”, the answer inevitably will be a manual scope, and particularly, an 8″ dob.

There are a couple of reasons for this.  One is because adding goto to a manual scope adds somewhere around $200 to the price of the same aperture scope without goto.  That’s $200 that might better be used to get a larger aperture manual scope.

But the real reason that others will give to stick with a manual scope over a goto is because, as they’ll inevitably say, “You’ll never learn the sky with a goto scope!”  Many people in this hobby tend to come on too strong to beginners and say, “You HAVE TO learn the sky.”  Well, the actual truth is that it just isn’t necessary.  Is it nice? Is it helpful? Does it get the chicks? Yes. (Well, I dunno ’bout that last one.)

There are a number of barriers to entering our wonderful hobby.  I, for one, in addition to welcoming our new computer overlords, don’t want ” . . . and you have to learn the entire sky” to add onto these barriers when goto scopes exist that completely alleviate that problem.

The analogy is GPS.  It might be nice to know in your head exactly how to drive from Lincoln’s home in Springfield, Illinois to City Hall in Waukesha, Wisconsin, but is there any need to know this anymore?  No!  And in fact, in this day and age, most people would say that it’s even stupid to memorize this, because the GPS in your car or on your phone will relieve you of having to know this information.

So it is with a goto scope.  The goto eliminates any need to learn where things are in the sky – it has all of them memorized already.  There is no need to know.

But, having said that, although there is no need, there should be a want.  You should want to know where stuff is in the sky.  Sounds like I just contradicted myself, right?  Well, no.

It is better to learn the sky because that way you generally know what’s out, what’s up, what you can see tonight. I’m not trying to discourage learning the night sky; on the contrary, I’m absolutely encouraging it. It’s just that you no longer HAVE TO.

Most goto scopes have a “Sky Tour” ability – press a couple of keys, and the scope will offer to show you objects that are above the horizon and therefore visible on any given night, at any given time.  The scope takes over.  You don’t need to know anything about the sky.  And as a rank beginner, that’s fine.  On the other hand, if you pay attention, the goto can teach you where things are, if you’ll take notice as to where it’s pointing, what constellation it’s aiming at.

A brief digression – using a goto scope will let you see 10 DSOs an hour for five minutes of observing.  And you can do that every hour, hour after hour (as long as your batteries hold up), and without having to look for and find the objects.  Yes, an old hand at starhopping can beat a goto scope in slewing from M22 to M57, and then to M13.  That’s certainly true.  But they won’t beat the goto going, say, from M20 to M27, and then to M56.  This, to me, is another reason for getting a goto scope.

Many of us have a limited amount of time to devote to this hobby.  On the one hand starhopping has an incredible sense of satisfaction – you used a star atlas of some kind and found the object yourself.  I know that feeling – it’s the thrill of the chase, of the hunt, finding your prey.  When you find it yourself by starhopping, you get a sense of pride.  But on the other hand, wouldn’t you rather be observing objects instead of just looking for them?

As a beginner gets a little more experience when you venture out in, say, July (as opposed to October, or January, or April), it’s better, more helpful, for you to have a good idea as to what’s up in the sky.  The constellations, the bright stars, sure, it’s good to know what’s out, what’s up in a larger sense like that.

I’m talking about going deeper than that, about knowing what’s up in terms of DSOs.  I’m talking about knowing that, okay, it’s July, that means Lyra is up, and, of course, the famous Ring Nebula, M57, is up, too.  But it’s nice to know that M56 – also in Lyra – is up as well, and you should go and observe that. Hercules is up, and that means, of course, M13 is up.  But M92 is somewhere in Hercules as well, so why not do a compare/contrast between these two globs and see which one you like better.  (I actually like M92 better.)

July also means that Sagittarius, or, as I like to call it, Greater Sagittarius, is up, and there’s a whole plethora of objects down south, from M6 straight through to M26 (and plenty more), that you should be observing.  You don’t need to know that M8 is near . . . whatever star it’s near.  You just let the goto know that information.  But you can bounce around and have the handset show you a good 25 objects in Greater Sagittarius, if you know which ones are up.

I think it’s better, more helpful to have a general knowledge of the sky like this – to know what’s up, where, and to be able to get excited about that, rather than just punching the “Star Tour” button on the goto handset and letting the computer completely take over. You don’t need to know this info, but you should want to know it; it’s better if you have an idea about it.

It gets right back to making astronomy sexy.  Knowing more about the sky will only help enhance your experience, make it more interesting.

Motorized Scopes

Before we get specifically to the goto scope, let’s distinguish it from a motorized scope.  For certain manual EQ mounts – especially the less expensive ones I mentioned at the very top of the page – you can add an electric motor onto them yourself for under $100.  This doesn’t transform the scope into a goto scope.  It just allows the formerly manual scope to now automatically track whatever you’re looking at – you can find an object, go away for a cuppa joe, come back 10 minutes later, and the object will still be somewhere in the field of view of the eyepiece.

Back in the day (30 to 40 odd years ago), this was called a clock drive, and was the only way to track that was available.  Fortunately, technology marches forward and we’ve moved past simple mechanisms like that.

Goto Scopes

A goto scope is a mount that has two motors as well as a way to control those motors – via a computerized handset.  Here’s a nice entry-level scope on an alt-az goto mount, one that I frequently recommend to beginners, especially those who live/observe from light-polluted skies, the Celestron NexStar 130SLT:

celestron-nexstar-130-slt-356-p
The Celestron NexStar 130SLT, around $400.

Okay, what have we got here?  There’s the aluminum tripod at bottom.  Sitting in a well at the top of the tripod is a round black plastic pod, and then coming up from that pod is an arm that holds the scope.  In both locations, inside that pod and inside the arm, there is a motor.   The motor in the pod moves the scope left and right (azimuth), while the motor in the arm moves the scope up and down (altitude).

Then there’s the handset, sitting in a cradle on one of the tripod legs and plugged into a receptacle on the pod.  There’s a computer inside of it that has the locations of about FORTY THOUSAND celestial objects in it.  Not that you can see all 40,000 of those objects through the 5 inches of aperture of the 130SLT.  They use that same handset and object database on all different aperture scopes.  The point is that if you’ve heard of the object, and if it’s bright enough, you can punch the object into the handset and see it through the scope.

After a very simple alignment procedure, you can press a couple of buttons on the handset to tell the motors what object you want to look at.  What is that alignment procedure?  In all of the handsets I’ve used, there is both a two-star alignment and a three-star alignment, among others.  You use the two-star alignment if you know the names of the two stars you want to align on.  You scroll down through a list of names, say, Vega first and then Altair, and then you look through the finder and use the handset to control the motors and point the scope first at one star, then at the other.  Once you’ve done this, the scope “knows” where it’s pointing, and therefore “knows” where everything else in the sky is.  You can now enter, say, M57 (the Ring Nebula) into the handset, and the scope will slew right there.

The three-star alignment is exactly like the two-star, except you don’t even need to know the names of any of the stars, and it is incredibly easy.  Let me repeat that, because many people simply do not believe this.  You point the scope at three bright stars – any three bright stars – that you don’t even know the names of.  The scope then figures out which three bright stars they are, and again, now “knows” where it’s pointing, and “knows” where everything else is in the sky.  Easy-peasy, lemon-squeezy.

You then punch into the handset whatever it is you want to see, and the scope slews over to that object.  Once it gets there, of course, the goto scope then tracks the sky as it moves (as the earth rotates on its axis).  Goto scopes do so a bit better than just adding a motor to a manual scope.  You can go get a cuppa joe and a danish and come back in 20 minutes, and the object should still be tracking somewhere in the field of view of the eyepiece, if you’ve left your 32mm Plossl in the focuser.

There is one very distinct disadvantage to most entry-level goto mounts:  you cannot use the mount if you forget your battery, or if your battery dies.  (Actually, these entry-level alt-az goto mounts generally take eight AA batteries, but it’s silly to use them, because the mount goes through them like candy.  Better to buy a rechargeable lithium powerpack to avoid having to spend money on batteries every time you take the scope out.)

Unlike a manual scope that you can obviously move yourself, most goto mounts do not have what is called “unlockable clutches” to allow you to move the scope around the sky yourself.  The two axes, altitude and azimuth, are usually geared to the motor, and you can’t move the scope – unless you completely strip the gears and destroy the mount.  Once you’re out of electricity, you’re pretty much done observing for the night.*

There is a notable exception to this – the Orion StarSeeker IV mount, around $500-700 depending on what scope you buy with the mount.

 

Orion-Telescope-N-150-750-StarSeeker-IV-AZ-SynScan-GoTo-Kit
The Orion StarSeeker IV 150mm reflector, $600.

This mount specifically has unlockable clutches so you can move the mount manually without ripping through the gears.  It also has optical encoders (like the red light and lens on the bottom of a computer mouse) so that as you do move the mount manually, the scope knows that you’ve moved it – and how much – and maintains its ability to track once you relock the clutches.

Look at the top of the arm of the SS IV 150, above.  That’s an unlockable clutch; there’s another at the base, too.  When you want to move the scope manually from one part of the sky to another, you unlock those clutches, move the scope, relock them, and then keep on observing.  Because of the encoders, the scope knows that you’ve done this and keeps tracking accordingly.

Why would you do this?  If you start off observing in one section of the sky, say the northeast, and now you want to observe towards the south.  Instead of 1) waiting for the scope to slew that whole distance (it can be a little slow), and 2) wasting all that battery power, you can just unlock the clutches and turn the scope south yourself.  A very handy feature.

Handsets

If you look at the different handsets for the different brands of scopes, you’ll notice that they pretty much all look the same.  They break down into two camps – the Celestron/Orion/Skywatcher on one side, and the Meade on the other.  The first three brands are all made by one factory in China called Synta; Meade makes its stuff separately.

NexStar handset
The Celestron NexStar handset.  There is now a NexStar Plus handset that is slightly different and a little better labelled than this one.

In the Synta handset, there’s a key pad of 12 keys, with ten numbers and two extra keys, like a telephone pad.  There are also three function keys at the very top, and in between the function keys and the keypad, there are four directional keys.  At the top of the handset is a two-line LCD display.  The whole handset is backlit with a weak red light so you can read the screen and the keys and you won’t lose your night vision.

But the differences between the handsets are more than cosmetic, not just on the outside.  It’s on the inside where there are significant differences.  Celestron calls its Synta handsets “NexStar”, while Orion and Skywatcher both use Synta handsets called “Synscan”.  Inside, the software that runs these handsets is quite different.  Celestron’s NexStar software is well-thought out and completely intuitive; the buttons for certain functions that are used frequently are labelled right on the handset.  Synscan handsets?  Not so much.

While goto scopes can be quite accurate, putting the object you’re looking for pretty much in the center of the field of view of your eyepiece, on some nights, for who knows what reason, they’re just not.  So, let’s say you performed your initial alignment on Vega and Altair, as I described above, more or less in the east.  Now you want to go look at M4 and M80, two globular clusters way down south in Scorpius.  Scorpius is basically on the other side of the sky from the Summer Triangle.

As the scope moves out of the area of the sky it was originally aligned to, alignment errors creep in.  The further you go out of that original area of the sky, the greater the error.  This results in a greater chance that the scope doesn’t put the object you’re looking for directly into the field of view of the eyepiece.  You’ll have to use the handset keys to move the scope around to hunt for it once the scope stops slewing.  Even then, the object will almost always be just outside of the field of view of your eyepiece.

When you do a big sky movement like this, it helps to “re-align” the telescope.  In other words, after you do finally get to the object that’s outside of the area where you originally aligned the scope, and the new object is in the field of view of the eyepiece, and centered, you tell the handset that you’re realigning on the new object.  With the Celestron/NexStar handset, there’s a button specifically dedicated to doing just that – Align.  It makes this re-alignment procedure as easy as can be.

On the Orion/Skywatcher/Synscan handset, you’ve got to go through about 8 button presses to get deep into a submenu to get to the align screen.  That’s very poorly thought out, and you’d never know how to do this unless you had brought the manual out observing with you.  And that’s just one example of how the Synscan handset is just plain more annoying, less intuitive than the NexStar; there are others.

For example, with the NexStar, how do you tell the scope to put the Ring Nebula in view?  You press the Messier button, then the 5, then the 7; hit Enter.  As soon as you press Enter, the scope immediately starts slewing right over to M57.  When you do this on the Synscan, it first shows you information about M57, then it asks you if you want to slew over to it.  Well, of course I want to slew over to it, ya eejut!  Nooooooooo, I just enjoy wasting time and learning information about these objects from a handset while I’m out observing.  Whoever programmed the Synscan was obnoxious.

As for the Meade handset, called Autostar, I haven’t used one in about a dozen years.  Back then, it was not very intuitive – I needed to bring the manual out with me every time I used the scope.  However, in the intervening decade, Meade has improved their handset software considerably so that it is on a par with Celestron’s.

With any of these handsets, if you don’t want to use the goto feature, you can still starhop to your little heart’s content, as long as you have juice.  (This shouldn’t be a problem; the rechargeable lithium batteries generally last about 8 hours, more or less, depending on the energy needs of your scope; more, if you get a souped up battery.)  All you do is turn the scope on, and then use the four-way directional controllers to move the scope wherever you want.  All of these handsets have a “rate” feature that lets you control the speed of how fast the scope slews.  For example, with the NexStar, the 9 setting is for moving around the sky quickly; the 6 is for centering objects in the eyepiece at low magnifications; the 5 and the 4 are for fine-tuning the location of the object in the eyepiece at higher magnifications.

Push-to Scopes

In between a completely manual scope and a goto scope there is a hybrid scope called the “push-to”.  Orion sells a bunch of dobs in their Intelliscope line that are not motorized, but are computerized, in apertures from 6 inches all the way up to 14 inches.  How does this work?

orion-skyquest-xt8i-intelliscope-dobsonian-telescope-2b8
The Orion SkyQuest XT8i IntelliScope, about $730.  Note that it costs over $300 more than Orion’s non-Intelliscope 8-inch dob, the Orion XT8, which sells for $400.

As with goto scopes, there is a handset.  After an alignment process, like the one I described above, you punch in the object you want to see.  But instead of there being a motor on the scope, YOU are the motor.  You push the scope while the handset essentially plays a game of “hot or cold” with you.  “More to the left.  More.  More.  Oops, too far, come back to the right.”  Then you do this with “up and down” = altitude, as well.  Obviously, it doesn’t do so with words, but with numbers on the handset that you have to zero out.  Once the handset reads zero in both axes, then the object should be in the field of view of your eyepiece.

The Intelliscope does this by way of optical oops, magnetic encoders.   This is similar to, but not exactly, how a computer mouse knows you’ve moved it.  Unlike today’s computer mouse that has an optical system that’s actually looking at the mouse pad (flip over a mouse and see!), the Orion system is mechanical/magnetic, sort of like a mouse from a decade ago that had that big hard rubber ball inside.  Each axis, azimuth and altitude, has an encoder that tells the handset how far that axis has been moved.  As the night goes on, the handset’s internal clock “tracks” the night sky in its memory , knowing that as time passes, the sky is continuing to move.

For starhopping purists, the push-to represents the best of both worlds.  You can use the scope purely manually and starhop if you want to.  Or, if you need some help finding an object, you can turn the Intelliscope feature on and let the handset guide you.  Since there are no motors, there are no batteries to wear down.  Well, there is just one – the handset operates off of a 9-volt battery, but it lasts a loooong time.

Goto Dobs

Most goto scopes are mounted on a tripod, like the Celestron 130SLT and the Orion StarSeeker IV 150 shown above.  Basically, all refractors, SCTs, and Maks are mounted on tripods as well.  Or more to the point, in terms of the refractors at least, the optical tube assembly (OTA – the scope itself) is usually sold separately, and you have to buy a tripod mount for them, which can be either manual or a goto.  SCTs and Maks are almost always sold on goto tripods.  But there is an exception to this, as well.

Celestron_11069_NexStar_8_SE_8_0_203mm_440829
The Celestron NexStar 8SE, the most popular SCT in the world, about $1200.

There’s another breed of goto scope that’s a little different:  the goto dob.  Obviously, this is a dobsonian mount with motors attached; you could think of it as an upgraded Intelliscope, obviously one with motors.

Orion skyquest xx16g
Orion SkyQuest XX16g, about $3700.

These goto dobs range from 8 to 16 inches, and both Orion and Skywatcher market these scopes.  For example, the Orion XX16g is $3700; Skywatcher’s 16-inch goto scope is $2950.  Other niche specialty dob makers sell these goto dobs as well, manufactured by hand here in the US, and are generally more expensive.  Orion and Skywatcher are the only mass vendors that sell these goto dobs.

Beyond these 16-inch goto dobs, Skywatcher also sells some pretty gorgeous 18-inch and 20-inch goto dobs, too, getting into the $7000 range.

dobson-18-stargate-skywatcher-oferta
Skywatcher Stargate Truss Dobsonian, about $7500.  If that ain’t making astronomy sexy, I don’t know what is.

Increasing Goto Accuracy

When you align a goto scope on two stars, then it can figure out where it’s pointing, and simply by that alignment, then the scope should know where everything else is.  Whether the scope is actually level or not shouldn’t matter.

But being level does matter. It soooo does. When I take the extra coupla minutes to get the scope really, REALLY level, it just gets that much more accurate when slewing to find objects.  Most goto scopes come with a bubble level mounted right into the mount.  You have to get that bubble right in the very center of that inner circle in the level on the mount to increase this accuracy.

Another thing is to make sure you’ve got it set to Daylight Saving Time.  Yup, this has happened to the best of us.  Ahem.  If the mount is set to Standard Time in your timezone when it’s really DST, your slews will be waaaay off.  Also, make sure the time, and more importantly, the date you’re inputting is correct.  12:30 am is the next day, so that could screw things up if you go out and start observing after midnight.  You have to input the next day if you do this.

On the other hand, I’ve found that inputting your latitude and longitude and the exact time down to the second are not exactly necessary.  The scope uses these bits of information only to calculate what the sky above you at your location looks like at any given time.  More to the point, what objects have risen above the horizon.  If, for example, you take the scope 60 miles west to a dark sky site, it might tell you that you can observe M31 a few minutes earlier than possible because the scope thinks you’re further east and M31 has already risen.  I’ve found that the precise latitude and longitude settings are not a big deal.

In terms of time, although I keep my watch (yes, in this day and age, I still wear a watch) set within a few seconds of official time, which you can get from NIST here, again, it’s not necessary to be completely precise here.  I’ve found that accuracy to within one minute is enough.

You always need to switch back to your finder eyepiece when you move from one object to the next.  For example, the SLT mount is pretty accurate, but it’s not perfect. You want to give it the best chance at finding the object by putting the eyepiece that has the widest field of view in the focuser – that’s generally the one with the largest number on it.  Most scopes come stock with a 25mm eyepiece.  To get the widest field of view ( = biggest patch of sky) possible to see through the eyepiece with a regular, 1 1/4″ focuser, see about buying a 32mm Plossl for about $35 or so.

Another important way to increase the accuracy of a goto mount is to align it the way the scope wants to be aligned.  When you do your original alignment or a realignment, before you press that “align” key telling the mount that you’re done, have the last two movements you make on the scope to center the object be the same way the scope was moving before it stops.

What I mean by this is, take a look through the eyepiece as the goto finds an object.  On its final movements to the object, the scope will approach the object from a certain direction.  In my SLT, it’s approaches the object from the bottom left of the field of view – the object comes in from the bottom left of the field and moves towards the center.  Your mileage may vary, so have a look.  When you’re doing those final centering movements in an alignment, first move the object to that bottom left quadrant of the eyepiece’s field of view.  Then press the up and right keys so that your final centering movements match the ones that the scope just did.  Then press the “Align” key to get that alignment precise.  (Or press the 8 keys that get you to the “Align” sub-menu.  Grrrr.)

This is important because it winds the gears up in the same way that the scope winds them up, the same way the scope expects them to be wound up.  And this increases goto pointing accuracy.


 

* This isn’t necessarily so.  At my astroclub’s monthly open house last week, one of the wires of my 4-year old Mak’s handset got frayed to the point where the handset no longer works.  (I’m currently seeing about getting it fixed.)  However, I met a beginner who really, really wanted to use her brand new Celestron NeXYZ phone mount to take some photos.

We made it work, even without any motors or tracking.  I could still get the scope on whatever target we wanted to look at by using my red dot finder and literally lifting up the entire scope and turning it to point it where I needed it to be.  (The SLT mount lets you adjust altitude manually, in a rough manner, but not azimuth.)  Then, as the object moved rightward in the sky with the rotation of the earth, we could pull back on the right tripod leg about a half-inch at a time to keep up with it as it drifted out of the field of view.  So, it is possible to use the scope without the motors; it’s just kind of a pain.

 

 

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5 thoughts on “July 27, 2018: Goto Telescopes / Mounts

  1. Jon

    The tip about the last two movements in the initial alignment process being the same directions the scope wants to travel when it ends it’s locating moves really are important

    And nice job on explaining subjects that have a lot of moving parts…some literally!

    Liked by 1 person

  2. Ok, you caught me, from now on I will level my mount. I promise. -Richard

    On Fri, Jul 27, 2018 at 7:43 PM Light-Polluted Astronomy wrote:

    > Jon posted: “So, let’s say you bought your first scope for around $150 to > $300 – maybe it’s the Astronomers Without Borders One Sky scope, or one of > its clones, like the Meade Lightbridge 130. Perhaps you’ve bought a > refractor, like the Meade Infinity 102. Or, it co” >

    Liked by 1 person

  3. An excellent explanation. Thanks for posting. All of the mounts you mentioned were Alt-Az mounts. I have found that 85% of the positive reviews for GO-TO mounts were for Alt-Az mounts. I have a GEM, specifically an AVX mount. I have wrestled with it for more than 3 years and I usually lose on getting it to find ANYTHING. I really appreciate your tips about using the align button to touch up the alignment and about the 3-star alignment not requiring you to know the names of the stars you are using. I will be trying both of those methods. I also bought a StarSense for my mount to make everything automatic. The manual couldn’t be less helpful if it were written in hieroglyphics. However, it does get me within 10 to 15 degrees of the target most times ! I AM impressed with the camera’s ability to see so many stars that are invisible to me. It’s just that my success rate of achieving a good Go-To alignment is 1 out of 10. Are equatorials really so much tougher to coax into a Go-To state of mind ? If I EVER nail down how to get my AVX to do Go-To reliably, I will post a simple step-by-step method that most anyone can understand.

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    1. Thomas, I haven’t heard of a difference between the reliability of alt-az and EQ goto mounts. The first thing that comes to mind is your polar alignment. Have you set the Dec axis to your latitude and then properly polar aligned? Not that I can give you any tips on how to do so well, as this is one of the reasons I stick with alt-az mounts – to avoid having to do polar alignment.

      Otherwise, what about your local astroclub – can they help you out? Beyond that, it looks like you should get in touch with Celestron customer service. You may not be doing anything wrong, but you may have a dud mount on your hands. Even though it’s 3 years out and outside of warranty, they may still be able to do something for you. Good luck!

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