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Alignment Stars Ambiguous

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6 replies to this topic

#1 Dennis Persyk

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Posted 09 August 2019 - 11:42 PM

I have a new LX200-ACF.  After going through the level north, tripod tip, ... setup, it slews to a star and requests I center the brightest star and press ENTER. 

 

Tonight both initial slews were in a region where there were 3-4 stars in the FOV of a 40 mm Ploessl eyepiece and they were all pretty much the same brightness.  I made my best guess and result was "Align Successful". I did a goto to the Moon and the moon was about 20 degrees off.

 

What do you suggest?

 

Thanks.
Dennis



#2 OzAndrewJ

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Posted 10 August 2019 - 12:21 AM

Gday Dennis

a) What firmware does it have loaded?

b) There is a menu setting to force the real star name to be shown

 

The moon can have odd calcs at times but not 20deg

I would redo the alignment with the correct stars selection and try again.

If you know the main bright stars, you are better off just doing a manual 2star

as you get to select your own stars ( and its much faster )

Andrew Johansen Melbourne Australia



#3 havasman

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Posted 10 August 2019 - 12:38 AM

Yes, pick your own stars. Use a shorter focal length eyepiece.


Edited by havasman, 10 August 2019 - 12:39 AM.

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#4 sg6

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Posted 10 August 2019 - 01:35 AM

First I would check how level and North the scope actually is - do not use magnetic North as that can be several degrees off and so therefore will the first slew. Thinking that the scope has slewed the required amount but as the start position was a bit off you have ended up looking at where the first alignment star was not present.

 

Assuming the 8" then with a 2000mm focal length you get 50x, and that gives 0.8 degree field. The catch then is that you need to be aligned to North by a maximum error of 0.4 degrees - not 0.8, things get halved.

 

So if more then 0.4 degrees off of North your first alignment star will not (OK may not) be in the field of view. That all means you have top be very accurate. One of the catches with an SCT.

 

An accuratelt set up finder will help, but accurate means checked at each outing to be confident of accuracy.

 

Easy way to envisage it is a star at 90 degrees to North. You set up scope to L&N, and then scope will slew 90 degrees to the first star. If your North is 1 degree off the final slew position is 1 degree "wrong", and in the field you have there is no alignment star in view. You have a field of view of +/-0.4 degrees and the star is off to one side by 1 degree = not in view.

 

Selecting your own is a good option as the best idea I have come across is to select red/orange stars at least for the first one. The color makes them stand out easier.

 

But I think the real problem will be the initial Level and North simply as you have a narrow FoV.

 

I do think that with an SCT (Meade and others) that Level and North although easy is maybe not a great idea. A start position of centering Polaris would make more sense. That is defined and can be read from data and it removes the "How level and how North?" is the scope question.



#5 OzAndrewJ

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Posted 10 August 2019 - 03:13 AM

Gday sg6

 

I do think that with an SCT (Meade and others) that Level and North although easy is maybe not a great idea. A start position of centering Polaris would make more sense.

No good for me :-)

Also, whilst the instructions say Level and North ( as its easy to understand ),

you are really setting the mount to Alt = Az = 0.

In a one or two star process, the mount assumes it is at alt = az = 0

"when you tell it to start the align" process ( ie it gives you a chance to put it into home first )

It then does a dead reckoning slew to the first star.

If you put the mount in the home position in AltAz,

and then turn it on and set the date/time you are actually aligned.

Just set tracking to astronomical and you could do a goto.

Slew to a known star and synch and you have effectively done a one star align.

 

Andrew Johansen Melbourne Australia


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#6 carolinaskies

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Posted 10 August 2019 - 07:02 AM

I have a new LX200-ACF.  After going through the level north, tripod tip, ... setup, it slews to a star and requests I center the brightest star and press ENTER. 

 

Tonight both initial slews were in a region where there were 3-4 stars in the FOV of a 40 mm Ploessl eyepiece and they were all pretty much the same brightness.  I made my best guess and result was "Align Successful". I did a goto to the Moon and the moon was about 20 degrees off.

 

What do you suggest?

 

Thanks.
Denni

You should be knowledgeable about the alignment star the mount is using, whether it picks it or you do.  Check on the hand control which star it has chosen and using a star chart (hand held or on your phone/tablet/computer)  Then looking at the sky where the scope is pointing does it appear to be generally pointed in the right constellation and location in the sky?  If it is then using the finder scope you should be able to see the alignment star is brighter than other stars.  Adjusting the mount hand control to bump the alignment star to the center of the finder again you should have a pretty good idea which star is the alignment star.  At 40mm your scope is seeing around .75-1 degree of the sky so you may want to drop to the 25/26mm which will put you close to 1/2 degree and the alignment star should be in that field of view.   

My bet though is you have something off, date, time, or location wise so your initial field is wrong because normally alignment stars are pretty easy to identify even in a 40mm widefield eyepiece. 


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#7 decep

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Posted 10 August 2019 - 11:57 AM

The LX200GPS mount has been a frustrating experience for me, as well.  smile.gif  It is considerably more complicated than I had assumed when I bought mine... especially without some guidance.

 

I have an older one that has not been updated for the recent GPS rollover, so I have my GPS disabled.

 

  1. Make sure date and time is right
  2. Verify GMT offset
  3. Verify Site (longitute/latitude)
  4. There is another GMT offset in the Site
  5. Verify Alt/Az or Polar config

 

Assuming you do not have a permanent pier.... Make sure every time you power it on, you calibrate sensors before you perform an alignment.  The end of the calibrate sensors routine should try to align on polaris.


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