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"GoTo" a little off

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#1 jeff408

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Posted 11 November 2012 - 01:00 AM

I have a LX200 10" gps and after aligning it. It seemed like everything was a little off. Like when I went to Juniper I had to slew over some on my own to get it in my FOV, then same thing with M42. Is there a way to let the telescope know when you have it centered so next time it will go right to it. I'm just wandering if I didnt mess up on 1 or both of the line up stars.

#2 neotesla

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Posted 11 November 2012 - 07:17 AM

Centering the alignment star can be a bit of a problem, a reticle helps, but you can also try defocusing the star until you get a donut, and that's much easier to center. Try that first next time and see if that helps, the GOTO's should have the target in the field of view on a low power EP's for the most part.

#3 Bill-in-BC

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Posted 12 November 2012 - 02:07 PM

After you press GOTO and slew to your selected object, center the object in your eyepiece and then press and hold ENTER for a couple of seconds. You'll then see the message PRESS ENTER TO REGISTER -- then press ENTER again and you're good to go (or GOTO) Bill

#4 faltered

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Posted 13 November 2012 - 04:47 PM

yes, centering the alignment stars is very important. Obviously a crosshair eyepiece would be the best way, but that isnt always an option. But at the very least start with a lower powered eyepiece, center as best you can, then increase your magnification with a higher powered eyepiece. I also then defocus the star a bit to make it a bit larger, making it easier to center.

Im sure this is not the case, but I have personally done this before....

One time I was lazy with centering my finderscope properly. So I thought the star I was centering was the one in the finderscope, but turns out it was a very close nearby star. So I actually centered the wrong star. But that was a one-time fluke for me.

And finally using the SYNC feature will help. Go through your alignment, then select an object (a named star would be best) and if its slightly off, center it manually with the hand controller then hold down ENTER for a couple seconds - it will then allow you to "sync" on that object.

#5 Bill-in-BC

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Posted 14 November 2012 - 11:48 AM

I was reminded last night that it should be PRESS ENTER TO SYNCH. Sorry about that. Bill

#6 AntMan1

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Posted 16 November 2012 - 06:21 PM

I read when you sync on one particular object lets say Saturn in the southern sky that when you goto another object it will be off. so the sync is good when observing 1 object for an extended period of time.

Don't know if you LNT or not but if not, leveling the tripod is very important also lining up the tube with true north very important since its more accurate then magnetic north.

I was reminded last night that it should be PRESS ENTER TO SYNCH. Sorry about that. Bill



#7 LoveChina61

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Posted 16 November 2012 - 07:39 PM

i have read others say that one should never Sync on one of the planets. The orbit of a planet is slightly more variable than that of a star's. You will trigger a slight variation in the scope's GoTo accuracy if you Sync on a planet. Best to just center the planet in one's eyepiece and let it track without actually Syncing on it.

Perhaps that distinction between planets and stars is mitigated if you are able to update the planetary orbits often (e.g. via Autostar). However, my LX200 Classic is basing its orbital calculations on information from year 2000 so the calculations will be very slightly off. It is best for me to just Sync on stars to achieve the absolute highest level of GoTo accuracy.

#8 KimB

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Posted 22 November 2012 - 11:57 AM

I don't think it's a good idea to sync on planets as their position is calculated each time. I agree I've found levelling the tripod helps. I have the LNT version of the LX90, and I found that the LNT module had some side to side movement in it and ended up putting a couple of blobs of hot glue on the mounting screws inside the cover so that's when it's calibrated it stays still. One other thing I've noticed is that the accuracy varies depending on what stars are used for alignment, some work better than others. Not sure why.

#9 thesubwaypusher

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Posted 24 November 2012 - 11:35 PM

I have a LX200 10" gps and after aligning it. It seemed like everything was a little off. Like when I went to Juniper I had to slew over some on my own to get it in my FOV, then same thing with M42. Is there a way to let the telescope know when you have it centered so next time it will go right to it. I'm just wandering if I didnt mess up on 1 or both of the line up stars.


Hi Jeff:

These telescopes can be extremely accurate. It just takes a bit of effort on your part. Calibrate the sensors and the home position once a year, level the tripod even though you may have the auto-tilt feature, point the control panel south, the corrector north, use a reticle eyepiece, and align the second star (the clock is ticking at this point) ASAP after the first.

Also, try not to use that sync feature unless you plan on staying in that part of the sky for a while. If you have to sync, something's wrong.

And very important- USE HIGH PRECISION POINTING! It is the best feature on these instruments.

Good luck, Chris

#10 Rick Woods

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Posted 25 November 2012 - 12:50 AM

Jeff,

I don't see it mentioned here so far, so I'll be the first.

How old is your LX200, and how old is the software version? If you don't update the software (as I never have), the locations of the planets get farther and farther out of date as the years go by. My LX200 is almost 10 years old, and still uses the original software. Go-tos to stars and DSOs are dead on; but the planets are a little more off each year.
It's a small computer in the telescope, and it's figuring the position of the planet based on its ephemeris when the software was new. It's calculations only go to a certain precision, and the small errors mount up with time.

So, don't worry about it. Do the go-to, then center it by hand. My software works great, so I'm not going to risk an update. Tough planets like Pluto, well, you never know when they're centered, anyway. If I really need a correct, current position, I refer to the Astronomical Almanac.

And PS: Don't sync on planets. That'll screw everything else up. That's another mistake I made before giving up and reading the manual.

#11 cavefrog

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Posted 25 November 2012 - 07:17 PM

That's another mistake I made before giving up and reading the manual.


Rick! you sound like a true Cajun!

(Cajun motto... if all else fails, read the directions!)

Theo

#12 Rick Woods

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Posted 26 November 2012 - 11:07 PM

Not a Cajun; but I sure liked Bourbon Street! :D

#13 thesubwaypusher

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Posted 01 December 2012 - 03:02 PM

How old is your LX200, and how old is the software version? If you don't update the software (as I never have), the locations of the planets get farther and farther out of date as the years go by. My LX200 is almost 10 years old, and still uses the original software. Go-tos to stars and DSOs are dead on; but the planets are a little more off each year.



I did not know this. Thanks Rick!

:bow:

#14 Rick Woods

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Posted 04 December 2012 - 12:09 AM

How old is your LX200, and how old is the software version? If you don't update the software (as I never have), the locations of the planets get farther and farther out of date as the years go by. My LX200 is almost 10 years old, and still uses the original software. Go-tos to stars and DSOs are dead on; but the planets are a little more off each year.



I did not know this. Thanks Rick!

:bow:


You're welcome.
The caveat is that this is strictly my own experience and deduction, based on what I've observed, plus 30 years in computer software development and maintenance. I didn't hear it from Meade or anyone else. But it just makes sense, and the behavior of the scope fits my opinion of the cause.
Just be aware that if you tell this to someone else, you're only quoting me, and not any particular authority.

Just sayin', in the interest of full disclosure! :D

#15 OzAndrewJ

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Posted 04 December 2012 - 04:21 PM

Gday Rick

Just be aware that if you tell this to someone else, you're only quoting me, and not any particular authority.



And you are right ;)
We looked into this last year after it was raised by another user,
and have put out patched data to fix it.
Basically, Meade use a mid level equation to calc the planet positions as JNow().
They then use an interpolation table to post correct this data for a better fit.
This is a std process that is used to reduce calculation data and time.
Unfortunately, the interpolation table appears to have been made relative to J2000 for all points, vs a rolling JNow().
As such they calc a rough JNow() then tweak it back to J2000 :question:
so all planets are using J2000 coords.

Andrew

#16 Rick Woods

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Posted 04 December 2012 - 04:28 PM

Well, thanks Andrew, it's nice to have confirmation! :)

So, does the JNow() function feed off the GPS fix? And what did you do to correct it, update the interpolation table? Will it need to be fixed again in a few years, or did you correct it for good?

#17 OzAndrewJ

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Posted 04 December 2012 - 05:42 PM

Gday Rick

So, does the JNow() function feed off the GPS fix?



Sort of.
It uses whatever date the scope is currently set to.
If you used the GPS, it is todays date.
If you fake a date via manual entry, it works to that date.

And what did you do to correct it, update the interpolation table?



Yep. There were 2 choices od fix
a) Fix the interpolation table.
b) Precess the data as calculated.
Even tho the interpolation table was for J2000, it appears it was based on PC calculations vs the lower precision the Hbx gives.
As such, there were lots of other errors due to rounding and precision, so a new interpolation table was the best way to fix it.

Will it need to be fixed again in a few years, or did you correct it for good?



Its a lot of data, so i have corrected up till the end of 2014 at present.
I have the data for later years, so will modify then if reqd.

Andrew






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