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can you still star hop on an EQ GoTo mount?

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#1 joelin

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Posted 19 July 2019 - 01:48 AM

Let's say I want to use my Orion Sirius GoTo to observe visually with my refractor. 

 

I'm not really clear how effective that is.

 

I mean I can do the initial 3 star align. It's a bit time consuming and can get me close to the first few GoTos, but after that it just builds up more and more error.

 

So after that I have to use the directional arrows to slew it around (very difficult to star hop in my opinion because the directions don't map easily to where I want to go) or do another 3 star align (after I turn it off)?

 

 



#2 sg6

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Posted 19 July 2019 - 02:08 AM

Yes, but that is not your problem.

To hop you just use the L/R U/D keys to move the scope to where you want.

 

Your problem seems to be not adding additional alignment stars or performing a Sync on additional stars as the goto goes to another. and so the errors build up

 

Suggest that on say every 3rd star/object you perform a Sync and have the mount have it's position reset to a star. Software kind of enforces this to occur.

 

Not sure actually if Sync and adding additional alignment stars are the same - if not someone should wander along and give just the adding alignment stars aspect.

 

If I am right Sync is select star, center star, press Esc or Return and hold down for 2 seconds. Mount then resets whatever position it believes it is at to the RA+Dec of the star on the handset display.


Edited by sg6, 19 July 2019 - 02:09 AM.


#3 Jon Isaacs

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Posted 19 July 2019 - 02:56 AM

In the past, when I have star hopped with a GOTO EQ mount, I have used it like a tracking mount but not a GOTO mount.  

 

I think nearly all, if not all, GOTO mounts have a EQ North and EQ south mode that doesn't not require alignment (other than manual polar alignment.)

 

I'd just turn on the EQ North mode, make the big slews by unlocking the clutches and do the final centering with the hand controller.

 

I prefer a manual alt-az mount but this works.  

 

Jon


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#4 oshimitsu

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Posted 19 July 2019 - 04:28 AM

It's my understanding that if you sync on a star to perform a precise goto you will have to remove that sync after ( at least that's what my celestron manual says )



#5 pierce

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Posted 19 July 2019 - 04:33 AM

I decided a long time ago that 'goto' was more trouble than it was worth, unless you had really high end gear like Astrophysics or Takahashi.    I can point my totally manual dob faster than most guys messing with a cihinese goto.


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#6 BQ Octantis

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Posted 19 July 2019 - 06:13 AM

I own an Orion SkyView Pro GoTo EQ mount, and I haven't done a 3-star alignment well over a year. I only rely on GoTo for "ball-park" pointing, and it's always good enough to get my AP target on my DSLR sensor. After your session, if you do a "Park Scope → Park Position", your 3-star GoTo alignment and PEC will be saved. The next time you power up, GoTo will give you the option to start from Park Position, which will restore your prior 3-star align and PEC. If you had a tight polar alignment when you did your GoTo, and you get a tight polar alignment on the current session, your only error will be the RA bias for your current session. You can remove this by telling GoTo to point at a star, and then loosening the clutch(es) and manually pointing scope at the star (it helps to have a finder scope with a crosshair aligned to where your objective is pointing). And if you leave your tripod out (like I do), your polar alignment error will be identical, and your RA error should be pretty minimal each time you start up.

 

Sorry if that's hard to follow. It's this simple:

 

Session 1:

Get tight polar alignment.

Set time & date accurately to the second.

Perform a 3-star align.

Utility Functions → Park Scope → Park Position.

 

Session 2, 3, …:

Get tight polar alignment.

Start from Park Position.

Set time & date accurately to the second.

Point to known star with GoTo.

Loosen clutch(es) and center star in scope.

Tighten clutches.

 

Alternatively, you could just use the clutches and your setting circles, just like you would with any other tracking tripod. Once you're dialed into a target, you can manually enable RA tracking under Settings → Tracking → Sidereal Rate.

 

Hope that's useful.

 

Cheers,

BQ



#7 macdonjh

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Posted 19 July 2019 - 07:34 AM

 

I'd just turn on the EQ North mode, make the big slews by unlocking the clutches and do the final centering with the hand controller.

 

 

Jon

With a SynScan controller (like what is supplied with the Orion mounts), you do this by not performing an alignment (when the controller prompts you to perform an alignment, simply choose "NO") and then using the menu to set the tracking rate the sidereal.  I think you set tracking rate in the Utilities menu, or perhaps in Set-up.

 

Star hopping is difficult with the SynScan mounts because they don't really have clutches.  A better description is axis locks.  They really have two "settings": engaged and disengaged.  For star hopping it's best to have clutches that are backed off a bit so there's some friction in the mount's movements, but not so much that the mount jerks when you move it.  Just like what Dobsonian owners want in their mounts.  

 

That said, I did star hop through the Messier list once (...once).  What I did was use go-to to slew my mount to a bright star in the object's constellation.  Then I'd use the hand controller to move the mount along my star hopping path.  One nice thing about using an EQ mount for star hopping is the mount's motions follow the RA and declination lines on your star charts (provided you have good polar alignment).  But a well adjusted Dobsonian-mounted Newtonian, to me, is the king of star hopping scopes.  Wide field and smooth motions; can't beat that.  Just try manually hunting for objects in my main scope, f/15 classical Cassegrain (maximum TFOV of 31').


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#8 Jon Isaacs

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Posted 19 July 2019 - 09:47 AM

With a SynScan controller (like what is supplied with the Orion mounts), you do this by not performing an alignment (when the controller prompts you to perform an alignment, simply choose "NO") and then using the menu to set the tracking rate the sidereal.  I think you set tracking rate in the Utilities menu, or perhaps in Set-up.

 

Star hopping is difficult with the SynScan mounts because they don't really have clutches.  A better description is axis locks.  They really have two "settings": engaged and disengaged.  For star hopping it's best to have clutches that are backed off a bit so there's some friction in the mount's movements, but not so much that the mount jerks when you move it.  Just like what Dobsonian owners want in their mounts.  

 

That said, I did star hop through the Messier list once (...once).  What I did was use go-to to slew my mount to a bright star in the object's constellation.  Then I'd use the hand controller to move the mount along my star hopping path.  One nice thing about using an EQ mount for star hopping is the mount's motions follow the RA and declination lines on your star charts (provided you have good polar alignment).  But a well adjusted Dobsonian-mounted Newtonian, to me, is the king of star hopping scopes.  Wide field and smooth motions; can't beat that.  Just try manually hunting for objects in my main scope, f/15 classical Cassegrain (maximum TFOV of 31').

waytogo.gif

 

I agree that the most mounts today are closer to locks than clutches but as you say, one can adjust them so they can be slipped. 

 

I think a fast refractor on an manual alt-az mount is the queen of star hopping scopes.  A 4 inch with a field of view of 4 degrees or more doesn't go as deep as a larger aperture Dob will but it's an easy, comfortable experience, gentler, a walk though the university with a fine lady.. 

 

Jon


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#9 ArkabPriorSol

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Posted 19 July 2019 - 10:00 AM

Star hopping using the directional keys is very frustrating, I feel your pain! Push-to star hopping is king for visual viewing. I also found using GOTO a lot more hassle than just push-to star hopping for the vast majority of my visual targets. The slewing speeds even at max are far slower than I can just simply push point the scope at the target. I had a Losmandy G-11 which was terrific for this because it would keep tracking perfectly even after manual push-to. EQ mounts with clutches instead of locks are the good for this. I agree with Jon, nothing beats a manual alt-az clutch mount for star hopping visual. GOTO is only valuable for finding really faint objects, or remote imaging.


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#10 macdonjh

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Posted 19 July 2019 - 12:55 PM

GOTO is only valuable for finding really faint objects, or remote imaging.

I disagree with this.  I completed the Herschel 398 in four nights' observing using go-to simply because I could go very fast through the list (I still have to see the North American Nebula and, I think, M101).  I'll admit I didn't do the list for Astronomical League credit, I was curious to see what objects were on the list and what they looked like.  The vast majority of them were faint fuzzies that my club's dark site rarely allows me to see well.  So I was content with, "saw it, move on".  There is no way I could have seen that many objects (100, average, on each of those nights) if I was star hopping and hunting.  

 

Even on normal nights when I am trying to be relaxed and actually observe an object, I prefer to enter an object's catalog number and let my mount slew to its location.  While my mount is slewing I move my chair and my eye piece case.  My mount and I are usually ready to look at an object at about the same time.  



#11 jdupton

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Posted 19 July 2019 - 01:42 PM

joelin,

 

   In answer to question posed in the thread title, yes you can star hop with a GoTo mount. However, it is done differently than you would typically do with an alt-az mount like a Dob.

 

   The key difference is that you need to move in RA and Dec as you hop rather than Altitude and Azimuth (up / down, left / right). Instead of looking at directions to move referenced to the Earth, you look in a star atlas to decide where and how much to move. It might go something like this.

  • Decide on a target
  • Find a bright nearby star you can easily center.
  • Slew the telescope (Manual or GoTo) to the area of the star and get the star centered in the finder and eyepiece.
  • Add an Alignment (PAE) star by using the method CN userid sg6 suggested. (Esc, Esc Hold, Centered, enter.)
  • Look at the Atlas and determine where the target is in terms of RA and Dec differences
    Example: "my target is 3° East and 5.5° South of this bright star.
  • Switch to the Utility Menu Show Position option of the hand control and look at the RA Dec display.
  • It should show the RA and Dec of your currently centered bright star.
  • Now drive the scope with the directional buttons until the display shows the RA and Dec of your target.
    You should be very close and hopefully have the target in the eyepiece.

   Note that SkyWatcher mounts don't technically sync when you add additional stars after your initial alignment. They add what is called a PAE (Pointing Accuracy Enhancement) star to the sky model. SkyWatcher firmware can add up to one PAE star for each of 85 "zones" in the sky. These PAE stars allow better accuracy near the star but not outside the zone the star is in. (Adding multiple PAE stars close together simply replace the prior PAE star for that same zone.)

 

   This is a little different from HPP (High Precision Pointing) and Sync used by some other mount brands. In those cases, the existing model of the sky can be shifted around so that your current target is at the expected coordinates. When you stray far from this point in the sky, the model can be off again (sometimes by a greater amount than originally depending on where you sync'ed and where you are going). With PAE, the sky pointing model is not directly changed but pointing the area of the PAE star is improved. Moving elsewhere in the sky uses the original sky model. If you happen to add enough PAE stars around the sky, your accuracy improves near each of them and is not affected by the additional PAE stars as can happen with a true sync.

 

   Sorry for the long post. I wanted to give you a flavor of what can go on behind the scenes. The net is that you can star hop but do it using the equatorial mount's RA and Dec directions and distances rather than earth-based directions and altitudes.

 

 

John


Edited by jdupton, 19 July 2019 - 01:56 PM.


#12 Wildetelescope

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Posted 19 July 2019 - 02:04 PM

waytogo.gif

 

I agree that the most mounts today are closer to locks than clutches but as you say, one can adjust them so they can be slipped. 

 

I think a fast refractor on an manual alt-az mount is the queen of star hopping scopes.  A 4 inch with a field of view of 4 degrees or more doesn't go as deep as a larger aperture Dob will but it's an easy, comfortable experience, gentler, a walk though the university with a fine lady.. 

 

Jon

This is why I like the Losmandy Clutch design.   My GM8 is the digital drive version, so there is no goto, only tracking.  The slip clutch works quite well for the star hopping and I use it often at my clubs open houses.  Not much of a star hopper, but I can usually hit the obvious targets without much trouble.   Simplifies set up in an area where what you see of the sky is limited by trees. You can do the same thing with the Gemini versions, but of course you will loose your goto model.  

 

JMD


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#13 joelin

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Posted 19 July 2019 - 02:36 PM

I'd be interested in seeing a video demo of how that works.

Anyone have one?

#14 F.Meiresonne

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Posted 19 July 2019 - 02:40 PM

Let's say I want to use my Orion Sirius GoTo to observe visually with my refractor. 

 

I'm not really clear how effective that is.

 

I mean I can do the initial 3 star align. It's a bit time consuming and can get me close to the first few GoTos, but after that it just builds up more and more error.

 

So after that I have to use the directional arrows to slew it around (very difficult to star hop in my opinion because the directions don't map easily to where I want to go) or do another 3 star align (after I turn it off)?

i had a HEQ5 in the past. For visual it was very roughly polar aligned. Still could track planets or other objects for at least 10 minuts and after that i had only to adjust either RA or DEC slightly to get it centered again.

Goto which does not exit at that time will probably off. but for visual with a tracking EQ it should not be that hard to cope with imo,jut point the scope on the object you want to see and you should be good...


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#15 t_image

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Posted 19 July 2019 - 03:58 PM

However, it is done differently than you would typically do with an alt-az mount like a Dob.

 

   The key difference is that you need to move in RA and Dec as you hop rather than Altitude and Azimuth (up / down, left / right). Instead of looking at directions to move referenced to the Earth, you look in a star atlas to decide where and how much to move. It might go something like this.

Another method is how I easily star-hop to the Clarke belt of Geostationary satellites.

Stellarium has a EQ projection mode and lots of helps like an Equator marking and an EQ grid....

Without adding too many details,

  • I conceptionally "view" star-hopping with a EQ as a matter of the Equator line as the neutral frame of reference.
  • I rotate my camera so my view has it flat with the equator.. (One can somehow do this FOV orientation with an eyepiece-tape for top mark?).
  • Then the L/R arrows only move the RA, going across the E-W....
  • Then the Up/Down arrows adjust the North away from the equator or South away from the equator.

Yes things get special as you get closer towards Polaris....But even that isn't too much of a challenge.

 

 

Not a visual person so I can't conceive of the calisthenics y'all do keeping your eye in the eyepiece while moving the scope,

hopefully most star-hops are small so this isn't an issue.

 

 

Also:

This is a more narrow use case than trying to star-hop across the entire sky,

I used to use my EQ mount to track planes at high mag...with camera (ie corrected view)...

If I can remember correctly it may have involved me reversing in HC menu  Left/Right or Up/Down and then I would hold the controller 'landscape mode' v. 'portrait mode' [to borrow concepts from cellphone] so that the up/down an L/R keys were associated with the orientated direction.

It may have also involved me flattening out the Lat., so such would not help with tracking on your subject one pointed....


Edited by t_image, 19 July 2019 - 03:59 PM.


#16 lsfinn

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Posted 20 July 2019 - 11:59 PM

I've done it with a 9.25" SCT on a CGEM. It's a pain. 

 

I've tried it two ways: first, without power and just using the clutch to hold the scope as I hopped using a telrad and a 9x50 straight-thru finder; second, with power and using the hand controller to slew about. 

 

In neither case did I do an alignment: after all, I was hopping. 

 

In principle it ought to be no more difficult than pushing around an alt-az, except that gimble-lock is located in the direction of the RA axis. In practice it's much more cumbersome: basically, a GEM is just not built with that kind of use in mind. 


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#17 pierce

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Posted 21 July 2019 - 12:19 AM

on my old Vixen SuperPolaris, which just has slow-mo motors I only occasionally connect to power, it came with the springy-knobs, I install those, loosen the motor clutches (NOT the ra/dec clamps) and turn them in RA and dec, and its not bad.

 

I prefer my photon cannons, err, dobsonians.



#18 sedmondson

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Posted 22 July 2019 - 02:52 PM

I've done it with a 9.25" SCT on a CGEM. It's a pain. 

 

I've tried it two ways: first, without power and just using the clutch to hold the scope as I hopped using a telrad and a 9x50 straight-thru finder; second, with power and using the hand controller to slew about. 

 

In neither case did I do an alignment: after all, I was hopping. 

 

In principle it ought to be no more difficult than pushing around an alt-az, except that gimble-lock is located in the direction of the RA axis. In practice it's much more cumbersome: basically, a GEM is just not built with that kind of use in mind. 

 

GEMs were used for star hopping long before GOTO scopes were common. I have located many an object using my 20+ year old GM8 mount with telrad and star atlas. The GM8 has true slip clutches, not engage/disengage locks, which makes it much easier. With encoders and a DSC, it can also be used as a digital push-to mount.

 

It is true that modern GOTO mounts are not made for star hopping. I wonder if mounts with "dual encoders", such as Atlas Pro (Az/Eq6) and Sirius Pro, can be used for push-to star hopping without losing alignment.



#19 ArkabPriorSol

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Posted 22 July 2019 - 03:52 PM

I'd be interested in seeing a video demo of how that works.

Anyone have one?

Here is a video of Scott Losmandy himself demoing how the clutch mechanism works on his mounts: https://www.youtube....h?v=uxu3Tmiic8M

There are two knobs, one on each axis, that you twist to adjust the tension on the clutch. You can twist one way to completely disengage the clutch and the axis will swing freely. Tighten the other way and the movement becomes stiffer. When you're using the tracking you want the clutch to be tight enough so that it doesn't slip. But perhaps loose enough so you can still push to objects when you want to. 

 

Man, I miss my Losmandy so much. Someday I'll pick up another G-11...



#20 Sarkikos

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Posted 23 July 2019 - 01:53 PM

I decided a long time ago that 'goto' was more trouble than it was worth, unless you had really high end gear like Astrophysics or Takahashi.    I can point my totally manual dob faster than most guys messing with a cihinese goto.

waytogo.gif  Goto slows me down.  I couldn't stand it.  It's like wearing a straight-jacket while trying to observe.  Not that I've ever done that.  But I have done goto.  Now I'm done with it.

 

Mike


Edited by Sarkikos, 23 July 2019 - 01:55 PM.

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#21 Sarkikos

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Posted 23 July 2019 - 01:57 PM

I had a couple GEMs with tracking but no goto.  Sure you can star hop to objects.  I did it all the time.  But star hopping on an alt-az mount is easier, in my opinion based on my experience.

 

Mike




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