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Equipment Discussions >> Mounts

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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Pointing accuracy new [Re: Eddgie]
      #6062954 - 09/04/13 04:09 PM

Quote:

The OP said he is getting 30 arc seconds now, but does not satisfy him. I would be thrilled with 30 arc second pointing, but apparently he is not.




He's apparently shooting at only 550mm so he'd never notice a 30 arcsecond error; that'd be only 15-20 pixels. I just presumed he got the unit of measure wrong.


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gdd
Pooh-Bah


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: Pointing accuracy new [Re: jrcrilly]
      #6063160 - 09/04/13 06:07 PM

Other than using pointing software, how about doing a GOTO an easily identifiable star near the intended target, sync to it, then do one more GOTO - would that get you close enough?

Gale


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inZet
member


Reged: 02/12/09

Loc: Milan, Italy
Re: Pointing accuracy new [Re: Eddgie]
      #6063228 - 09/04/13 06:57 PM

Thank you all for the answers! Mods moved my post, I almost missed it... :-)
I mainly observe and measure double stars. To be sure I'm measuring THAT double a good pointing precision is important, otherwise errors can be performed.
My setup is very lightweight. I have a short tube (WO Megrez 90), rings, dovetail, ASI120 webcam, cables. 5 Kilograms payload at most, the Sphinx SXD specs are 15 Kg max.
I observe from my backyard, on grass. Tripod is HAL130, aluminium, it seems sturdy but who knows? I never thought about flextures. It may be a land subsidence, do you believe pieces of wood under the tips may help?
Balancing is a nightmare, axes are frictioned, they come very tight from Vixen. However, if possible I unbalance east to let the gears to always be in traction.
The SXD is not an HEQ5, it is supposed to be well-build (???), in fact I'm not aware of an hypertune: the weak link in the chain is the electronic, but replacing the StarBook with the NexSXD solves all the problems and transforms the mount in a Celestron AdvGT/CGE Pro. I've not bought the HC, I'm using NexRemote software to control the mount.
I don't have too much money to invest, AP is not a solution.
Even with the best mechanic I learned from you it's hard to achieve necessary precision; a plate solve is required. The question is if a solve can be found even if small fields are imaged.
The camera has 3.75 um pixels, imaging scale is 1.3 arcsec/pixels, near the scope's resolution limit.


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inZet
member


Reged: 02/12/09

Loc: Milan, Italy
Re: Pointing accuracy new [Re: gdd]
      #6063251 - 09/04/13 07:14 PM

Good idea to sync on a near star. Because I usually observe nearby doubles, I should need to sync only one time per zone.

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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Pointing accuracy new [Re: inZet]
      #6063265 - 09/04/13 07:21 PM

Quote:

Good idea to sync on a near star.




Just turn on the "Precise goto" function in the controller. That won't get you within 30 arcseconds but it will get you closer than you are now if you aren't using it - probably within an arcminute or so.


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inZet
member


Reged: 02/12/09

Loc: Milan, Italy
Re: Pointing accuracy new [Re: Eddgie]
      #6063306 - 09/04/13 07:57 PM

I meant arcmin, of course. 30 arcsecs is the separation of Albireo... I only want to get the double in the field, I don't do position measurements. :-)

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WesC
Carpal Tunnel
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Reged: 02/06/13

Loc: La Crescenta, CA
Re: Pointing accuracy new [Re: jrcrilly]
      #6063308 - 09/04/13 08:00 PM

So far the only thing that affects my CGEMs gotos are how well I align those calibration stars and tripping over the tripod in the dark!

If I get those two things right, my gotos are well within 20% of the center of my 11mm Nagler. And if I need dead-center tracking, I just sync to that object.

Good enough for me.


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jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Pointing accuracy new [Re: inZet]
      #6063309 - 09/04/13 08:00 PM

Quote:

I only want to get the double in the field, I don't do position measurements. :-)




Precise goto will get you where you need to be without having to buy anything.

As soon as C integrates the starsense with the precise goto function it will be automatic. Then I'd buy the Starsense.


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rmollise
Postmaster
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Reged: 07/06/07

Re: Pointing accuracy new [Re: inZet]
      #6063489 - 09/04/13 10:26 PM

Quote:

I meant arcmin, of course. 30 arcsecs is the separation of Albireo... I only want to get the double in the field, I don't do position measurements. :-)




I don't know about this rig you are using, a Vixen with somebody's motor control board that allows you to use the NexStar HC, but Celestron's mounts will EASILY get your target in the field of such a small wide field scope if the alignment is done correctly.


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orlyandico
Postmaster
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Reged: 08/10/09

Loc: Singapore
Re: Pointing accuracy new [Re: rmollise]
      #6063539 - 09/04/13 11:11 PM

He's using the ASI120 which has a teeny tiny chip (probably equal to or smaller than a Mallincam chip). I think his problem is more of the soft ground (yes, wood under the tripod tips would help) and maybe not using UP and RIGHT for all final alignment corrections.

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rmollise
Postmaster
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Reged: 07/06/07

Re: Pointing accuracy new [Re: orlyandico]
      #6063955 - 09/05/13 09:00 AM

Quote:

He's using the ASI120 which has a teeny tiny chip (probably equal to or smaller than a Mallincam chip). I think his problem is more of the soft ground (yes, wood under the tripod tips would help) and maybe not using UP and RIGHT for all final alignment corrections.




Good catch...


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Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Pointing accuracy new [Re: Spacetravelerx]
      #6064032 - 09/05/13 09:43 AM

Quote:

Quote:

Quote:

Rod is right. Unfortunately Celestron still has no competition when it comes to go-to pointing accuracy. Celestron software is still the most complex when using HC only. Skywatcher/Orion are still lagging behind in software go-to precision.




Um, I have to dispute this claim "Celestron still has no competition...".

My LX850 provides excellent gotos (i.e. spot on), and I am pretty certain the same is true for the LX600. Like I said, once I am back home in New Mexico I will use my MallinCam to show how good the Meade setup is.

I cannot speak for all the other Meade units, but I simply have wonderful gotos on my LX200 and LXD75, though qualitatively speaking the LX850/LX600 are better. This is also one of many reasons I chose Celestron over Meade.






I have to agree. I've used both systems and Meade is way ahead of Celestron on ease of alignment and even the fine tuning process. Meade's Easy Align uses two stars that the GPS finds for you and it is as accurate as Celestron's 2+4 system..

Celestron is a popular option for refractors and why they can't simply their alignment process and make it more like Meade's is beyond me.


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rmollise
Postmaster
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Reged: 07/06/07

Re: Pointing accuracy new [Re: Jon_Doh]
      #6064188 - 09/05/13 10:58 AM

Why? Part of the reason is that Meade sued them over their GPS 2-star alignment process for alt-az GPS scopes.

The other part is that for a _GEM_, a two-star alignment really doesn't work worth a frak.

Edited by rmollise (09/05/13 11:33 AM)


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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: Pointing accuracy new [Re: rmollise]
      #6064197 - 09/05/13 11:02 AM

And I have found the Celestron alignment easy enough and accurate to better than +-5 acrminutes. Granted the only Meade goto I am familiar with is the ETX80 I have so I won't compare accuracy, but for ease I wouldn't say it is all that much easier.

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inZet
member


Reged: 02/12/09

Loc: Milan, Italy
Re: Pointing accuracy new [Re: Stew57]
      #6076588 - 09/12/13 09:17 AM

Wood under the tripod tips helped for sure.
Two days ago one of the rays that sustain the accessory tray broke, so I suspect the crack caused lack of rigidity.
Repaired in time for a quick check, now I can have the pointed object within 10 arcmin from the center of the eyepiece.


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Gil V
professor emeritus


Reged: 09/09/12

Re: Pointing accuracy new [Re: inZet]
      #6076659 - 09/12/13 10:03 AM

What is an acceptable error for visual use, in your opinion? Is 5-10 arcminutes acceptable? I've just installed DSCs and I'm still in the learning curve.

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rmollise
Postmaster
*****

Reged: 07/06/07

Re: Pointing accuracy new [Re: Gil V]
      #6076754 - 09/12/13 11:00 AM

Yes, 10 or 15-minutes is pretty good.

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Gil V
professor emeritus


Reged: 09/09/12

Re: Pointing accuracy new [Re: rmollise]
      #6077269 - 09/12/13 03:24 PM

Thanks, Rod. I measured about nine arc minutes of error in my Dynamax mount over 12 hours. Frankly, I'm suprised it wasn't a lot worse.

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Ranger Tim
scholastic sledgehammer
*****

Reged: 03/25/08

Loc: SE Idaho, USA
Re: Pointing accuracy new [Re: Gil V]
      #6077989 - 09/12/13 11:25 PM

You are using a reticle eyepiece for your reference stars, correct? I use a 9mm reticle eyepiece and get great go-to's with both my Sphinx and my GM-8. Most are dead center unless I am flopping back and forth over the meridian. Error tends to build if I work both hemispheres alternately. I stay in one then switch.

With a reticle ep for alignments I can get my mount set-up for a visual run easily. When imaging I use a camera and zoom the live view to the maximum to center alignment stars. Hey, it works!


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inZet
member


Reged: 02/12/09

Loc: Milan, Italy
Re: Pointing accuracy new [Re: Ranger Tim]
      #6079098 - 09/13/13 05:09 PM

I use a webcam and a software that plots a reticule on the screen. It's far more precise than eyepieces.
Beware to use full CCD resolution; most drivers use the upper-left frame only. For example if your camera has a 1280x1024 pixels and you select 640x480, you bet those pixels aren't in the center of your imaging area.
The result is, if you use a flip mirror, you could see the star not in the center of your eyepiece! Or, if you align based on 640x480 setup, it's like to align with the star not in the dead center of your eyepiece -- you can imagine the effect on pointing precision.

Gianluca


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