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A question about GO-TO mounts

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#1 chitown

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Posted 21 February 2009 - 11:18 PM

Hi guys, I have a very basic question about goto mounts. I would be buying my very first one soon and was confused about this:

Do you have to setup 3 star alingment (or similar procedure depending on the manufacturer) and polar alingment everytime you move your mount?

For example, you move your mount from your backyard to frontyard, do u have to perform this procedure to aling all over again?

Thanks
;)

#2 Steve Fisher

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Posted 21 February 2009 - 11:24 PM

Chitown:

Welcome to Cloudy Nights.

The answer to your question is Yes! One of the drawbacks to computer aided scopes.

#3 stevecoe

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Posted 21 February 2009 - 11:36 PM

Chitown;

I have an Orion Sirius Mount, it is a dream. I set up and align on TWO stars each time I move the mount, but it never takes longer than the length of twilight. So, as long as I am setting up the scope by the time the ball of the Sun goes over the horizon, I am ready to observe once it is dark. Once you get good at it, long before then.

Yes, it would be somewhat a pain in the butt, if you were going to observe in the backyard for an hour and then move to the frontyard for new objects.

Hope that helps;
Steve Coe

#4 Lane

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Posted 21 February 2009 - 11:57 PM

chitown - some scopes require you to know where the alignment stars are at in the sky and some do not. Once you aim the Sirius mount at polaris for instance and then pick your first alignment star from the list, the scope goes to that star automatically, all you have to do is center it in the eyepiece. Depending on how well you aimed at polaris the alignment star is usually in the FOV of a low power eyepiece. Same thing for your next alignment star. The whole procedure from lining up on polaris to finishing the alignment procedure is only about 3 minutes. Now if you get a scope that does not automatically find the alignment stars for you then you need to know exactly where they are in the sky so you can find them. That can be a problem unless you learn in advance where those stars are located. If you have to figure out where they are during the alignment process you could be aligning for 20 minutes.

#5 Dave H.

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Posted 22 February 2009 - 12:53 AM

Hi Chitown,
Welcome to CN :grin:

As already indicated, the short answer is yes, GOTO/automated mounts must always be aligned with the sky so the mount's electronics can be synchonized with the mount's electronic celestial database, and then slew accurately to find distant celestial objects.

If this is all new to you as seems possible, you might want to consider one of the Celestron Alt/AZ automated GOTO telescopes with the Nexstar software. While these Nexstar Alt/AZ GOTO scopes do of course require an alignment each time you use them, one of their big benefits to the novice is they do not require you to have any real knowledge of the night sky, and you can learn as you go.

When aligning a german equatorial mount such as the popular CG5 or the new CGEM that I use, you must start by doing a polar alignment, or at the very least pointing the mount roughly at the North celestial pole which is very close to Polaris, the North Star. Then you must "align" the mount with at minimum 2 known alignment stars for the mount to deterime its position. With just a little practice this alignment process becomes pretty routine, but none the less if one does not actually align on the correct stars to correspond to those selected in the mount's hand control, the GOTO functions will not work as the mount will be unable to synchonize with its celestial database.

To some degree this same pricipal applies to Alt/AZ mounts, but the polar alignment is not required.

With the Celestron Nexstar Sky Align you literally just point the scope at any 3 bright objects to perform the alignment and it makes no difference if you know the names of the objects or for that matter if one happens to be a planet or even the moon, then the scope itself determines which 3 objects you just pointed at, and performs the alignment automatically. With just a little practice on simple tasks like centering the alignment stars in the eyepiece and leveling the tripod, amazingly accurate GOTOs can be achieved. I was out with my little C6 and a small Nexstar mount this evening and the mount was consistently placing selected GOTO objects in the 68 degree field of view of a 15mm eyepiece.

For more information read the data on this link, and by the way I have no affiliation with Celestron at all, but like many, I am a big fan of the super simple Nexstar Sky Align.

Hope this helps!
:jump:
http://www.opticspla...align-info.html

#6 ragebot

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Posted 22 February 2009 - 02:13 AM

I suggest you down load a manual for a GOTO mount and read up on just what the alignment process consists of.

In general you need to polar align and level a GOTO mount; and somehow enter basic data like lat/long and time.

However most peeps who use such a mount at their house will somehow "mark" where they set up their mount in the back and front yards (maybe by drawing circles around the tripod legs or placing those rubber circles you can buy at Lowes where they will place the tripod legs).

Keep in mind that most GOTO mounts have a "slew to park" and "park scope" command on the controller. So once you spend say 1/2 an hour polar aligning and leveling your mount you do your observing then "park" the mount.

If you have marked where you set up the scope you can then carry it inside and put it away; and the next time you want to observe simply set it back up on your marks.

I observe from the patio at my house and always set up in the same place. I can carry the mount out to the patio and set it up on the pads on my patio and be observing in less than five minutes.

For a better explanation read what the manual says about parking your mount.

#7 FoxTrot

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Posted 22 February 2009 - 06:58 AM

Hi Chitown, I agree with all of the above. Before I had my LXD75, my alignment was always pretty rough and hap-hazard; my previous mount's polar alignment scope was useless (for the S hemisphere), and neither did I know how to drift align. But it took me only one night with the LXD75 to appreciate how easy the whole thing is with these modern (and only entry-level) CG-5 mounts. Both Nexstar and Autostar automatically select alignment stars for you anyway. As stated above, with other Goto handcontrollers, you may have to more knowledgeable about the sky when it comes to alignment star selection. It takes me only minutes to polar align very adequately for visual use - so if the mount has to be moved, it's no hassle to re-align very quickly. Fox.

#8 Kaizu

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Posted 22 February 2009 - 07:19 AM

The answers are basically yes and yes.
I'm lazy and sometimes I cut so that I align my G11 roughly visually and then turn it manually to home position and then start it by "warmstart". Next I align it by one star. If I'm going to observe Virgos galaxies, I first synchronize the mount to Regulus and then go to the final target. So the error is so small that I can find the target. This way is not precise and does not work on astrophotos but it works when I observe visually using small magnification. This way is faster and some time I hurry before the clouds arrive.

Kaizu

#9 Luigi

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Posted 22 February 2009 - 08:35 AM

Of course you can! All you have to do is put the mount down in the same orientation to within a few arcmin... but most find it easier to do a realignment.

#10 hfjacinto

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Posted 22 February 2009 - 08:54 AM

I took my scope out and had it alinged in under 10 minutes. I then realized that it was too close the patio table so I moved it over a couple of inches and did a 3 star alingment in under 5 minutes. The alingment was so accurate that I seeing all the M objects I had picked in a 5MM EP, didn't even use the finder.

#11 jgraham

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Posted 22 February 2009 - 09:10 AM

Okay, I'll buck the trend; if you're careful the answer may be no. I align my mount only once or twice a year, even less if I don't have to. With my Autostar-controlled telescopes when I'm finished for the night I use the Park Scope function which stores the alignment information in memory, moves the scope to the home position, and asks you to turn the power off. The next time I set my scope up I return it to the home position manually before turning the power back on (if I'm using my LXD75 I use the polar scope to align the mount with the pole). After I turn the power back on the mount behaves as though it had been aligned using the alignment information it saved from the last session. The first thing I do is GoTo a bright star and this first GoTo is usually off by a degree or so to a couple of degrees. I center the star using the controller and synch the mount; on Autostar controllers you press and hold the Enter key for 5 seconds to activate the synch function, then press Enter again to synch the mount. After that my GoTos are spot-on. This is a very handy and time saving procedure as I move my scopes around quite a bit and often alignment stars are blocked from view.

#12 rmollise

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Posted 22 February 2009 - 09:31 AM

Chitown:

Welcome to Cloudy Nights.

The answer to your question is Yes! One of the drawbacks to computer aided scopes.


Well...as they used to say in the rent-a-car ads, "not exactly." :lol:

First off, if you want superior go-to accuracy, yes, most mounts require 2 - 3 - more alignment stars. HOWSOMEEVER...if you just want to do a little casual observing, no. Most mounts/scopes have options like "1 star," "Solar System Align" (align on the Moon or a planet), or "Quick Align" (no alignment stars at all, just assume you are aligned and start tracking). That makes a go-to mount no different from a non-go-to, and I find that useful for public outreach events where I just want to show off the Moon and the kids are too excited to wait till I can see alignment stars.

Go-to fork mounts do not require any polar alignment at all. German go-to mounts? Some require a fair polar alignment; some like the CG5 can be WAY off.

Well, yeah, if you pick up the mount and move it to the front yard, sure you do. Wouldn't you expect to have to polar align a non-go-to mount so it would track if you did that? ;)

#13 ragebot

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Posted 22 February 2009 - 10:09 AM

I have to repeat my OP in this thread and say you need to down load a manual and read it at least to the extent that you understand the commands "slew to park" and "park"; or the relevant commands on your mount.

I also find it interesting that of the 11 responses to your question only two (mine and Johns) even mention "parking" or "home position", which I take to mean the same thing but are used by different vendors.

Basically what we are saying is that the way you shut down your mount affects how you start up your mount; and this is well explained in the manual you get with the scope.

I find it very easy to return my tripod's legs to the place where I last used it and simply turn it on and slew to an object (in my case the sun) and observe it.

On the other hand I have noticed that many old school observers simply dont understand that once you have parked a scope if you change the position of the OTA manually you do have to realign.

Yesterday I was at an outreach event and one of my clubs most experienced members manually adjusted the OTA of one of my solar scopes on a GOTO mount to get the sun in the FOV instead of using the arrows on the controller. As a result I had to re-align the mount.

Bottom line is with a GOTO scope your life will be much easier if you understand how to park the scope before you turn it off; or to make it even simpler RTFM.

#14 Steve Fisher

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Posted 22 February 2009 - 12:44 PM

Well, yeah, if you pick up the mount and move it to the front yard, sure you do. Wouldn't you expect to have to polar align a non-go-to mount so it would track if you did that? ;)


So the answer to the original question as posted by the OP is yes?

Excellent answers with regards to park features guys.

#15 ragebot

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Posted 22 February 2009 - 01:34 PM

Well, yeah, if you pick up the mount and move it to the front yard, sure you do. Wouldn't you expect to have to polar align a non-go-to mount so it would track if you did that? ;)


So the answer to the original question as posted by the OP is yes?

Excellent answers with regards to park features guys.


I would say the answer is maybe; and a lot of the maybe is based on just how far it is from the front yard to the back yard.

On multiple occasions I have moved my stuff in the middle of observing sessions and not had to re-align anything; especially if I used the "sync" feature.

While I have never tried it I would bet you could poor a 4'X4' concrete pad in the front and back yard and install rubber pads on the concrete pad based on a well aligned setup and then simply move the rig from one concrete pad to the other with no alignment necessary. Other methods of marking the location of the tripod legs would work just as well if you were careful and you "parked" the mount before you moved it. If you were able to keep the power to the mount on you might not even need to "park" the mount; which seems unlikely to me but the back/front yard distance is the key to keeping the power on.

Also keep in mind that most GOTO mounts have a "sync" feature that allows a reasonably aligned mount to sync to an object in the FOV to correct for minor errors; which makes it even easier to move the location of a mount a short distance with minimum effort.

#16 rmollise

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Posted 22 February 2009 - 05:04 PM

Well, yeah, if you pick up the mount and move it to the front yard, sure you do. Wouldn't you expect to have to polar align a non-go-to mount so it would track if you did that? ;)


So the answer to the original question as posted by the OP is yes?


More like "not that different than a NON go-to GEM."

;)

#17 Steve Fisher

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Posted 22 February 2009 - 06:38 PM

You runnin for office this fall?

#18 Steve Fisher

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Posted 22 February 2009 - 06:41 PM

Rod:

By the way, I enjoyed todays blog. 02/22/09

#19 rmollise

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Posted 22 February 2009 - 08:29 PM

You runnin for office this fall?


Depends on how much the exalted office of Dogcatcher pays. :lol:

#20 rmollise

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Posted 22 February 2009 - 08:30 PM

Rod:

By the way, I enjoyed todays blog. 02/22/09


Thanks! I always REALLY enjoy doin' the "stroll down memory lane" thing. :cool:

#21 mischief

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Posted 22 February 2009 - 09:12 PM

To Steve Fisher: I love your quote, "Never try to teach a pig to sing, It wastes your time and it annoys the pig". (Robert Heinlein)
Dorothy :lol:

#22 Steve Fisher

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Posted 22 February 2009 - 09:43 PM

Dorthy:

Thank you! I cannot tell you how many times in my adult life I have been frustrated beyond words and when just about to blow I have had this quote run through my mind.

Raising kids, raising grandkids, working with the public or any one of a thousand other times. Sometimes you just have to realize you are wasting your time arguing.

#23 chitown

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Posted 23 February 2009 - 08:53 AM

A wealth of information, thank you good friends.

#24 ragebot

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Posted 23 February 2009 - 09:48 AM

A wealth of information, thank you good friends.


On re-reading your original question it just dawned on me that while some posters answers were directed to how you would use a GOTO GEM you did not specify if you were getting, or considering, getting a GOTO GEM or a GOTO AA.

I have both a GOTO GEM and a GOTO AA and the process I use to set them up before observing is significantly different.

A GEM mount is defined as a German Equatorial Mount while an AA mount is defined as an Alt-Azimuth mount. Without getting into too much detail both mount types have advantages and disadvantages.

I would point out that AA GOTO mounts far out number GOTO GEM mounts and are often marketed towards folks who want the easy solution to a GOTO mount; examples would include the Meade ETX mounts, the Celestron NextStar mounts, and a whole lot more.

While you did not say so in your original question, I inferred the reason you are moving your rig from the front to the back yard is because you have a different view of the sky in both places, e.g. a North sky view from one and a South sky view from the other.

This is a very common issue, and one an AA mount is usually much easier to deal with than a GEM mount.

Most GEM mounts have a polar scope which is used to polar align it, and it goes with out saying you need a good view of the North Star to do this. Many AA mounts only need to be roughly pointed north, and in some cases the directions in the manual are to point it South, which means you dont really need a good view of the North Star.

While both GEM and AA mounts do need some type of polar alignment my experience has been it is much less critical with an AA mount than a GEM mount. By the same token AA mounts seem to stress in the manual the importance of "sync to target" type commands to correct errors in polar alignment. In fact many AA mounts are quite able to track after a rough "point it North or South" when you set it up, "slew to target" and "sync" to target. While the same thing can be done on many GEM GOTO mounts the GEMs seem to assume a better polar alignment than the AA mounts do.

I would also point out that while there is not complete agreement if you ask a question about a specific mount say ETX GOTO mounts or Losmandy Titan GOTO you may get a more specific answer to what you need to do after moving the mount.

#25 chitown

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Posted 24 February 2009 - 08:30 AM

Thank you guys, excellent responses. Park feature is something to look at.

Can you tell me, if I have the optional GPS module installed on the mount, would alingment procedure any easier?






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