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LX 90 GoTo Seems a Bit Off?

Meade
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#26 OzAndrewJ

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Posted 28 October 2019 - 06:17 AM

Gday Blackbelt

 

 

I'm beginning to think my expectations may have been too high with a GoTo scope.

Nahhh. When set up and aligned correctly,they are pretty accurate for stellar targets.

Just needs practice and using the right align stars

 

 

 

The "Press Enter for 4 secs" is not in the Meade manual;

Yes it is but its in the "how to use the Autostar" manual, not the LX90 manual

 

Andrew Johansen Melbourne Australia



#27 Piet Le Roux

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Posted 28 October 2019 - 11:23 PM

Well it is actually 2 seconds or more and its on page 11 of the LX90ACF/SC manual.....

 

" ENTER Key: Accesses, in a sequential manner, the next menu or data level in the AutoStar
database. See MOVING THROUGH AUTOSTAR'S MENUS, page 18 and MENU AND MENU
OPTION DESCRIPTIONS, page 24.
NOTE: If ENTER is pressed for two seconds or more and then released, AutoStar
emits a beep and “ENTER to Sync” is displayed. “ENTER to Sync” is relevant only
after the telescope has been aligned and is pointing at an object. If the “ENTER to
Sync” feature is accessed by mistake, press MODE to return to the previous screen.
See HIGH PRECISION, page 29, for more details about this feature."


Edited by Piet Le Roux, 28 October 2019 - 11:24 PM.

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#28 Piet Le Roux

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Posted 28 October 2019 - 11:30 PM

PS talking about the manual : we are always looking for information at other places but the information in the manual on page 44 about collimation is for me the best guide for SCT collimation! 


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#29 Blackbelt76

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Posted 29 October 2019 - 05:07 AM

PS talking about the manual : we are always looking for information at other places but the information in the manual on page 44 about collimation is for me the best guide for SCT collimation! 

I was amazed my LX90 was still collimated after being shipped from nearly 2,000 miles across country; amazed and thrilled as I

get no pleasure collimating anything! LOL I have ordered 3 thumb screws from Bob's Knobs. I can just see myself reaching around to the front secondary

with a Allen wrench and scratching the corrector plate.


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#30 Blackbelt76

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Posted 01 November 2019 - 08:12 PM

Hmmm?

Very frustrating tonight.

 

Verified date, time, DS Time, scope model etc.

 

Leveled tripod & scope...used Polaris as my true north.

 

I allowed the AudioStar to choose the 2 alignment stars. Vega & Altair. I understand Vega is very high in the sky at my location,

so wondering if this is a poor choice for the alignment stars?

 

Also tried the "ping pong" test as Meade suggested. Yep, after alignment, the scope would slew to them (well centered) when I entered them in as GoTo objects...did this several times and each time the scope would slew accurately to Vega, then Altair and back to Vega etc...

 

Then I selected M57 Ring Neb..slewed right to it, no problem..but then again, it's very close to Vega.

 

Then I said GoTo moon. Missed it by what I consider a country mile; at least 10 degrees low.

Saturn; same..10 or so degrees low or below Saturn.

 

Is it possible these two stars Vega & Altair are just very bad choices for alignment stars?

 

Also tried pressing "Enter" for 2 secs, "sync to object" after centered and enter again. Nope..missed the next GoTo object by at least 10 degrees again.

 

I'm having a difficult time convincing myself this GoTo should be so difficult to setup & align.



#31 OzAndrewJ

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Posted 01 November 2019 - 11:56 PM

Gday Blackbelt

 

so wondering if this is a poor choice for the alignment stars?

I never had much luck with very high alignment stars

What is your general location and align time???

Can you see your pole star???

What i find gives the best aligns is to pick stars between say 30 to 45deg alt and 90deg apart in az

and preferably one each side of the pole.

 

Then I said GoTo moon. Missed it by what I consider a country mile; at least 10 degrees low.

Saturn; same..10 or so degrees low or below Saturn.

The moon is very iffy, as the mount only has a very limited code set and processing power, and the full moon calculations just dont fit in.

Same for the planets.

IIRC, the planet coords are also calculated for J2000 not Jnow and this affects results depending on the time of year. Simple test, use a planetarium program to calc the current coord of your planet.

Now select it in the handbox and hit enter so it calcs the position

The Hbx should be close to J2000.

Andrew Johansen Melbourne Australia



#32 Blackbelt76

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Posted 02 November 2019 - 05:43 AM

Gday Blackbelt

I never had much luck with very high alignment stars

What is your general location and align time???

Can you see your pole star???

What i find gives the best aligns is to pick stars between say 30 to 45deg alt and 90deg apart in az

and preferably one each side of the pole.

The moon is very iffy, as the mount only has a very limited code set and processing power, and the full moon calculations just dont fit in.

Same for the planets.

IIRC, the planet coords are also calculated for J2000 not Jnow and this affects results depending on the time of year. Simple test, use a planetarium program to calc the current coord of your planet.

Now select it in the handbox and hit enter so it calcs the position

The Hbx should be close to J2000.

Andrew Johansen Melbourne Australia

Thanks OzAndrew.

 

My location is northern Indiana. approx 41N

Align time around 8pm, although I tried several (re-alignments) over a period of 2 hrs.

I certainly can see the pole star and have used it for polar/true north.

 

I am beginning to believe the resolution/accuracy is very poor if I use high (+) declination alignment stars. (i.e) Altair & Vega.

This would certainly explain to me why M57 was well centered following a GoTo command, but no other objects were that are

located lower in DEC and further east or west in RA.

 

Interesting to note the "misses" were all as far as I can tell; declination errors (Pointing below the object), not so much in RA.

 

Still unsure "why" when I slew to the first alignment star (Vega), why it misses it by 10 degrees or so?

2nd alignment star Altair was at least in the Telrad, 2 degree ring.

 

I'm not giving up. Next time out I will be using 2 different alignment stars lower in sky and about 50-100 degrees apart in AZ.

 

PS: Once object is centered, scope tracks w/o a problem.

I would think (if) the alignment was off, it would not track?


Edited by Blackbelt76, 02 November 2019 - 06:06 AM.


#33 OzAndrewJ

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Posted 02 November 2019 - 06:17 AM

Gday blackbelt

I am beginning to believe the resolution/accuracy is very poor if I use high (+) declination alignment stars

I assume you mean high altitude here??? and if so yes, i have found that.

Have attached a rough plot of the available Meade align stars for your rough location at 8PM

Vega and Altair look horrible ( to me )

I would suggest trying based on Alkaid then Caph or Mirach

and see what happens.

Andrew Johansen Melbourne Australia

AlignStars.jpg


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#34 Blackbelt76

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Posted 02 November 2019 - 09:19 AM

Gday blackbelt

I assume you mean high altitude here??? and if so yes, i have found that.

Have attached a rough plot of the available Meade align stars for your rough location at 8PM

Vega and Altair look horrible ( to me )

I would suggest trying based on Alkaid then Caph or Mirach

and see what happens.

Andrew Johansen Melbourne Australia

attachicon.gif AlignStars.jpg

Yes..for sure I will.

..and yes...when I say (+) declination, indeed higher in my sky.

As your map shows, Vega is nearly at zenith at 8pm at my location.

I'll report back when I get a clear night; looks like it may be several days; typical November for Indiana..very cloudy.

On a positive note; I did get to try out my Telrad Finder...truly a great advantage over the 9x50 when roughing in positions.

Makes start hopping much easier too with the graduated reticle.

Appreciate your responses.

 

Clear skies and good seeing...



#35 Blackbelt76

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Posted 03 November 2019 - 07:30 AM

Success!

 

@ OzAndrew: Vega and Altair were bad choices made by the AudioStar. We had suspected this and this morning at 4am I confirmed that.

 

I chose Alioth and Regulus as my two alignment stars this morning.. What a difference!

 

The GoTo worked perfectly as long as I stayed in the eastern part of the sky where my alignment stars were located relative to my local meridian.

 

I learned if I slew past my local meridian to the western half of the sky, accuracy falls off somewhat; but a simple "synch" on a nearby known star

realigns the system, but only to a point. It seems better to just do another two star alignment if I plan to hang out in a certain part of the sky.

So maybe just (2) alignments per evening or morning, one for East of my local meridian and one for west.

 

My 2 hr session was cut a little short; noticed my Telrad began to fall prey to the dreaded dew of death. LOL. Makes sense as I have it positioned pretty close to my EP position; body heat warming the Telrad....but at least the main corrector & mirror stayed dew free with my home made dew shield.

 

I also learned leveling while important does not have to be perfect for visual only tracking.

I was able to level and setup, ready to observe in about 15 minutes.

 

Once again, a big thank you to all for your advice and guidance.

 

Glad I got this practice in before it really starts to get cold here. smile.gif


Edited by Blackbelt76, 03 November 2019 - 07:30 AM.

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#36 Piet Le Roux

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Posted 03 November 2019 - 09:57 AM

You can "bypass" the aliment star that Audiostar has chosen by pressing the down scroll arrow, it will choose another one . I believe the best aliment stars are at about 60 degree altitude and directly north and south, but that's not always possible so you take the ones closest to that. You said: "  ..used Polaris as my true north." we don't have a star like that but I have always wondered how it would be done with a Az/Alt LX90? Do you just line it up across the OTA? because ounce you have done the levelling I would not loosen the Alt lock, just point it to north and lock the Az.    


Edited by Piet Le Roux, 03 November 2019 - 09:58 AM.

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#37 OzAndrewJ

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Posted 03 November 2019 - 02:47 PM

Gday Blackbelt

Good to hear its working properly.

The LX90 really is a pretty accurate beast when set up properly

 

I learned if I slew past my local meridian to the western half of the sky, accuracy falls off somewhat; but a simple "synch" on a nearby known star

Again possibly due to the align stars you used. They were 60 deg apart in Az but both on one side of the meridien.

I try to get one each side of the pole for best results

for example, at 4am, i would have chosen say Phad and Shedir

 

I also learned leveling while important does not have to be perfect for visual only tracking.

I was able to level and setup, ready to observe in about 15 minutes.

Correct. The LX90s in altaz track by working out the Alt/Az for the current RA/DEC now() and a set time in the future. They use the align model to do this conversion, and then work out a motor rate required to achieve it.

As such, the align model assists in gotos and tracking.

 

On top of this,centring the target stars accurately also assist in the align model

How do you do it?? ie xhair EP, or just guess centre??

If tha latter, if you heavily defocus on the first star, you get a big donut and it is much easier to centre this in the fieldstop. Slew to the second star ( without refocussing ) and centre.

Once done, reset the focus correctly and you should be away.

Andrew Johansen Melbourne Australia


Edited by OzAndrewJ, 03 November 2019 - 04:35 PM.

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#38 Blackbelt76

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Posted 03 November 2019 - 03:59 PM

You can "bypass" the aliment star that Audiostar has chosen by pressing the down scroll arrow, it will choose another one . I believe the best aliment stars are at about 60 degree altitude and directly north and south, but that's not always possible so you take the ones closest to that. You said: "  ..used Polaris as my true north." we don't have a star like that but I have always wondered how it would be done with a Az/Alt LX90? Do you just line it up across the OTA? because ounce you have done the levelling I would not loosen the Alt lock, just point it to north and lock the Az.    

Yes, that is exactly how I get true north. Polaris is easy to see as a naked eye star here. Approx 41 degrees Alt here.

I get it in the Telrad, Go to the main scope and use something around a 18mm EP, center it and done; I then lock the AZ/RA and lower the OTA (Dec) and level it. 
This will be very handy when I get the wedge next year as I still remember how to compensate for Polaris not being perfectly Celestial north.

 

I agree, two stars located around 45~60 degrees In altitude closer to the celestial equator, with one North of it and one South will probably be even better.

 

Thanks again for all the help, I was beginning to get quite frustrated.

As said, I’m not a newbie to astronomy or scopes, but am new to GoTo scopes.

So far I’m enjoying the capabilities of it. My new mantra may become; 

setting circles?...we don’t need no stinking setting circles”


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#39 Blackbelt76

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Posted 03 November 2019 - 04:16 PM

Gday Blackbelt

Good to hear its working properly.

The LX90 really is a pretty accurate beast when set up properly

 

Again possibly due to the align stars you used. They were 60 deg apart in Az but both on one side of the meridien.

I try to get one each side of the pole for best results

for example, at 4am, i would have chosen say Phad and Shedir

 

Correct. The LX90s in altaz track by working out the Alt/Az current RA/DEC now() and a set time in the future

They use the align model to do this conversion, and then work out a motor rate required to achieve it.

As such, the align model assists in gotos and tracking.

 

On top of this,centring the target stars accurately also assist in the align model

How do you do it?? ie xhair EP, or just guess centre??

If tha latter, if you heavily defocus on the first star, you get a big donut and it is much easier to centre this in the fieldstop. Slew to the second star ( without refocussing ) and centre.

Once done, reset the focus correctly and you should be away.

Andrew Johansen Melbourne Australia

O

on top of this,centring the target stars accurately also assist in the align model

How do you do it?? ie xhair EP, or just guess centre??

Yep, just a guess. I usually use low power EP after it slews to the 1st alignment star then go to the main scope with something like a 13-18mm EP and "guess at center.

Are you finding the AFOV at lets say 13mm not quite accurate enough?

I would think or hope such a narrow FOV at those higher magnifications should be sufficient?

 

..and yes, see my post above; I will choose two stars next time out on opposite sides of my local meridian and closer to 50-60 degrees apart in AZ.

Still, with the two I chose this morning, I was quite impressed.

 

Thinking about some short exposure time AP with my DSLR, then stack.

Saturn is dropping fast in the SW for me by 8pm and Jupiter is even lower.

 

Looking forward to using a wedge next yr. I'm sure with the required corrector tripod adapter plate for the 8" and the wedge itself will no doubt cause some flex issues. I may just go back to a GEM; though I've spent enough money already this year. ;)

We shall see. Auto guiding will be a new adventure for me next year. Back in my younger days, we had to guide by hand visually..and the exp times were much longer...no stacking software in those days. LOL..cold cameras, film, gas hypered film.

 

Your input has been much appreciated.

 



#40 OzAndrewJ

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Posted 03 November 2019 - 04:41 PM

Gday Blackbelt

 

Are you finding the AFOV at lets say 13mm not quite accurate enough?

I normally use an astrometric reticle EP for aligning if i want accuracy, but otherwise, i find the defocus trick works much better than a focussed star

ie next time you centre a star, defocus it and see how much easier it is to judge centre.

 

 

 

and closer to 50-60 degrees apart in AZ.

Try for 90deg apart in AZ as your target, as it maximises the offsets for the tip/tilt calcs

 

Andrew Johansen Melbourne Australia


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#41 Piet Le Roux

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Posted 04 November 2019 - 12:07 AM

Yes, that is exactly how I get true north. Polaris is easy to see as a naked eye star here. Approx 41 degrees Alt here.

I get it in the Telrad, Go to the main scope and use something around a 18mm EP, center it and done; I then lock the AZ/RA and lower the OTA (Dec) and level it. 
This will be very handy when I get the wedge next year as I still remember how to compensate for Polaris not being perfectly Celestial north.

 

I agree, two stars located around 45~60 degrees In altitude closer to the celestial equator, with one North of it and one South will probably be even better.

 

Thanks again for all the help, I was beginning to get quite frustrated.

As said, I’m not a newbie to astronomy or scopes, but am new to GoTo scopes.

So far I’m enjoying the capabilities of it. My new mantra may become; 

setting circles?...we don’t need no stinking setting circles”

 

I find that getting my OTA level even if the tripod has been levelled, a bit difficult so part of the process is to keep rotating it 180 degrees, I then adjust the Alt until the error is the exact opposite then I rotate 180 degrees. At the end of this exercise, when the OTA and tripod are level, I would not touch the Alt knob again and would rather risk having a less accurate true North. 


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#42 Blackbelt76

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Posted 04 November 2019 - 06:08 AM

 

Yes, that is exactly how I get true north. Polaris is easy to see as a naked eye star here. Approx 41 degrees Alt here.

I get it in the Telrad, Go to the main scope and use something around a 18mm EP, center it and done; I then lock the AZ/RA and lower the OTA (Dec) and level it. 
This will be very handy when I get the wedge next year as I still remember how to compensate for Polaris not being perfectly Celestial north.

 

I agree, two stars located around 45~60 degrees In altitude closer to the celestial equator, with one North of it and one South will probably be even better.

 

Thanks again for all the help, I was beginning to get quite frustrated.

As said, I’m not a newbie to astronomy or scopes, but am new to GoTo scopes.

So far I’m enjoying the capabilities of it. My new mantra may become; 

setting circles?...we don’t need no stinking setting circles”

 

I find that getting my OTA level even if the tripod has been levelled, a bit difficult so part of the process is to keep rotating it 180 degrees, I then adjust the Alt until the error is the exact opposite then I rotate 180 degrees. At the end of this exercise, when the OTA and tripod are level, I would not touch the Alt knob again and would rather risk having a less accurate true North. 

 

Yep..I've done that too and seem to get pretty close to a level OTA as I rotate it thru 360 degrees.

I have however also noticed a slight bit of "play" at the base of the scope mount.

(i.e) If I grab the scope by its handles after its been leveled, and pull back and forth with slight pressure, you can see

where it rotates in RA is not perfect.

 

I'm not dissatisfied at all with this as it really is not all that bad. My hunch is that Meade put most of the R&D money into the optics; less so with the mount

system. I've read the LX 200 is a beefier mount and has more teeth in it's drive gear for smoother tracking when pressing the scope into AP service.

..but at nearly $1,000 more, the LX 90 was a wiser purchase for me as my interest is more visual than AP.



#43 Blackbelt76

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Posted 07 November 2019 - 09:00 AM

Interesting.

Last night for the first time, I tried 1 star alignment.

Only was looking at the moon since most deep sky objects were glared out.

I was surprised with ONE star how well it did...

..was NOT in the scope EP but was in the 9x50.

Did a go to to the Pleiades, about 90 degrees AZ to the east; again in the 9x50. 



#44 OzAndrewJ

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Posted 07 November 2019 - 03:20 PM

Gday Blackbelt

Yep, A one star will work perfectly well if your Az axle is vertical.

Andrew Johansen Melbourne Australia


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