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osteomark
sage
Reged: 05/09/07
Posts: 478
Loc: Oswego, NY
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Do you have to be perfectly polar aligned to have accurate goto? I'm using 26mm EP. Tripod is level, balanced scope and polar aligned (toward Kocab by 1*). Zip code correct and Daylight savings YES. I did not center on Polaris.
When the hand controller picks Vega it is 2* off then I center it. It then chose Kocab. I was a little closer this time. I centered and entered. Alignment is a success it said. It found M13 perfectly. It did not find M57 so I centered and Synched it. I tried for M31 and it missed by about 2*. I centered and Synched. It's good goto for immediate area but as soon as I goto M15 or M57 again I have to each time center and synch.
I notice back lash it the RA. Does this it self affect the Goto?
I'm really befuddled because the night before I had excellent goto and now I don't. I'm hoping that its just the polar alignment.
Also I have not done the "training" on terrestrial objects since I bought it used. Is this something that is necessary to be accurate?
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Meade LX50 8"SCT
Magellan II autofinder
WO 1.25" binoviewer with 3-in-1 Sieberts OCA
Marcus Luden Intes Micro 703 Maksutov 7"
Meade LXD55 GEM mount
Syracuse, NY
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22472
Loc: NE Ohio
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Quote:
Also I have not done the "training" on terrestrial objects since I bought it used. Is this something that is necessary to be accurate?
Yes. "calibrate motors" optimizes the decoder circuitry. If not performed, the controller will "miss" encoder pulses and accuracy will suffer. Drive training tells the controller how much backlash is present so it can compensate for this. Without it, the unavoidable backlash in the system will degrade accuracy.
Other comments:
You didn't mention whether you are using a two star or a three star alignment. The two star alignment presumes that the "LXD55 Adjust" procedure has been performed, meaning that the optical tube has been carefully aligned to the mount (meaning there is zero "cone error"). The three star alignment doesn't make this presumption, so it will be much more accurate than the two star if the optical tube isn't perfectly square with the mount.
The Autostar's Synch function refines accuracy within a narrow portion of the sky, at the expense of the rest of the sky. It's a shortcut way to gain precision in an area of interest without realigning - but it can only degrade overall performance elsewhere. With proper drive training and a three star alignment there should be no need to Synch - accuracy should be good everywhere.
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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME
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osteomark
sage
Reged: 05/09/07
Posts: 478
Loc: Oswego, NY
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John,
I used the Easy alignment which is 2 star. I did not know that with the 3 star. Thanks. I've got to do the training part then. OK hopefully that will fix it. Doe the train on terrrestrial have to be a mile away object though? I don't have that kind of distant at my house.
Thanks again,
Mark
--------------------
Meade LX50 8"SCT
Magellan II autofinder
WO 1.25" binoviewer with 3-in-1 Sieberts OCA
Marcus Luden Intes Micro 703 Maksutov 7"
Meade LXD55 GEM mount
Syracuse, NY
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1744
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Backlash in RA shouldn't cause pointing error if you do the setup properly.. This is because the setup routine always approaches the stars from the same direction, and the manual says that when doing the final centering, YOU should do the same.. I believe that they recommend that you use the North ("Up') and East ("Right") arrow buttons to do the final centering. What this does is that it ensures that you are always approaching the star from the same direction so that any gear lash has been taken up as the motor drives.
If you do have a lot of gear lash though, and you do your final alignment using the South or West buttons to move the star into its exact final position (the LAST button presses should always be North and East)then you can indeed introduce inaccury into the system.
As mentioned, there is also Cone Error.
But there is also the possibility that the mount is shifting (Braces weren't thight, or the legs settled, or the Vibration pads compressed unevenly over the course of the evening, etc).
Still, all of these factors togeter should throw the scope off more than a degree. But it does all add up...
If you set up on grass,especially if the ground is not quite level, use small peices of plywood or vibration suppression pads or something to keep the legs from settling unevenly.
Ensure that everything is TIGHT.
Always bias the balance the same way (in other words, make sure that either the Telescope size or the counterweight side is loaded more than the opposite side and be consistent. I usually load the counterweight side a bit more than the telescope side. This is because as I change from Heavy Naglers to light plossls, I don't want the scope to suddenly be heavier on the opposite side, which influences how the gear train receives pressure.
ACCURATE polar alignment is not essential, though approximate polar alignment (within 2 degrees) usually gives quite reliable pointing.
Even if you ellimate gear lash (which might or might not be something you want to do), these other factors can still affect pointing. I have had times where my mounts just didn't want to behave.
And don't be afraid of using Precise Go-To or Sync. That is what they are there for. YOu can spend a lot of time piddling around with alignment and not observing, or you can do an alignment and it it is off a bit, just Re-sync on a bright star in the area and do some good observing in that area.
But if you DO jump around the sky quite a bit, your setup routine (both Alignment and mechanical) needs to be refined and methodical to ensure that you will get consistent Go-tos. I have also found that on longer focal length scopes, eliminating the cone error greatly aids in all thigs to do with pointing, so as a previous poster said, it may be something to consider.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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osteomark
sage
Reged: 05/09/07
Posts: 478
Loc: Oswego, NY
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Eddgie,
Thanks. Good info. I did see the Precise Goto but it was getting late so I did not do it. What is it?
Are you saying that I can just center Polaris and that should be OK. I felt I was out in now where land when I tried going 3/4* toward Kocab.
Thanks,
Mark
--------------------
Meade LX50 8"SCT
Magellan II autofinder
WO 1.25" binoviewer with 3-in-1 Sieberts OCA
Marcus Luden Intes Micro 703 Maksutov 7"
Meade LXD55 GEM mount
Syracuse, NY
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1744
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Like John C's post, the Sync and the Precision Go-TO are just "Shortcuts" to help ensure that you are getting to your target if your alignment is a bit off.
With the Precision Go-To, when you put in a target object, the telescope will compute the location of a bright star that is relativly close to the object you want to go to.
It will then slew to that target first and prompt you to center the target in the eyepice.
When you have done that and hit the Enter button (or whatever.. the exact proceedure is in your manuao) the scope will use the encoders in kind of a "Default Mode" and simply step off the correct number of degrees from Precision Go-to target to the intended target. It takes a bit longer if you do this, but if you are jumping across a big peice of sky, or if you are looking for something at th VERY edge of detection and you want to be POSITIVE that it is in the field, the Precision Go-to usually is the best way to ensure that the target gets into the field.
SYNC will work as well, but the issue with Sync is that only the brightst stars in the sky can be used to Sync.. With Precison Go To, the telescope will often select a dimmer target star that is CLOSER to the intended target. The shorter the distance between the alignment star and the intended target, the more centered in the field it will be. In general, I find it to be the more precise way to find many many deep sky objects that are more than a few (1Hr, 10 degress in DEC) from a bright star if your alignment is poor..
Sometimes when I don't SEE the target, even if think my alighment is GOOD, I use Precision Go-To to go back to the spot to see if it returns me to exactly the same place... If it takes me back to the same place, and I can't see the target, then I know that it is because it is to hard for the conditions or the scope, but I know that I am looking at the right spot...
Yes... ON the LXD55, LXD75, and CG5, Centering Polaris is more than good enough. Your pointing will be just as good as if you do an accurate polar alignment.
What WON'T be as good though is "Long Term" tracking. In other words, depending on the mount, if you just do a rough align, the initial seek to the target will be accurate.. But if you go inside and knock down a sixer, have some chips, and watch a couple of innings of the big game, when you get back, the object will have drifted north or south from the field.
Now this doesn't HURT anything. I mean you can simply hit the Go-to button, and the mount will take you back to the target.
Uasually, the drift is so small that while the target is slowly moving away from the center of the field while observing, you will get tired of looking at the target and be ready to move on before it drifts far enough to be bothered by it, unless you are using a particulary large telescope where the field is quite small... I never accuratly polar align my C14 though, and rarely is the drift bad enough to bother me, even though I observer at 300x and 440x all the time.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22472
Loc: NE Ohio
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Quote:
Doe the train on terrrestrial have to be a mile away object though? I don't have that kind of distant at my house.
Thanks again,
Mark
The easiest thing (with a temporary setup) is to rotate the mount 90 degrees so the RA axis points East or West. Then you can use Polaris for drive training. Then reposition the mount to its correct orientation and do your star alignment.
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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME
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osteomark
sage
Reged: 05/09/07
Posts: 478
Loc: Oswego, NY
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John,
Super. Thats easy enough. If I use Polaris then it should only rotate in the EP when taking RA from East to West. Right?
Thanks,
Mar
--------------------
Meade LX50 8"SCT
Magellan II autofinder
WO 1.25" binoviewer with 3-in-1 Sieberts OCA
Marcus Luden Intes Micro 703 Maksutov 7"
Meade LXD55 GEM mount
Syracuse, NY
Edited by osteomark (09/04/08 03:07 PM)
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rutherfordt
super member
Reged: 05/07/06
Posts: 114
Loc: Blountville, Tennessee USA
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I have noticed that sometimes the pointing accuracy of my LXD55 suffers-- this is usually due to slippage in the gearing. Also, the pointing accuracy when the mount is on its tripod is much worse than when I have it mounted on my concrete pier-- there is quite a bit of flex in the legs, it appears.
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Tom Rutherford
10-inch f/6 Homemade Dobsonian (Cave mirror)
8-inch f/6 Homemade Dobsonian
6-inch f/5 Meade SN6
6-inch f/10 Celestron C6
5.5-inch f/3.6 Celestron Comet Catcher
66mm f/6 WO Petzval
2-inch f/15 Nippon Kogaku (my first telescope)
assorted unassembled pieces and parts
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osteomark
sage
Reged: 05/09/07
Posts: 478
Loc: Oswego, NY
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Hey all,
Well I did the easiest thing last PM. I used the 3 star align: Vega, Koceb and Deneb. I polar aligned on Polaris.
I'm floored. Using a 26mm EP, Started with M13 and got it,
M57, yep, further away M15 great, then M 27 and ye haw and finally m29 bingo. So I feel like I went around the sky abit and everything was in the EP and nearly centered!
I did the North and East last button use also.
Does the North and East mean that is direction the scope moves becuase the buttons don't corelate that way because in the EP the image is inverted right.
So at this point I feel the 3 star align was the answer.
I discovered I may not need the polar aling scope becuase I have a green laser and man that thing is awesome to use for the alignment. As long as you can see Polaris with naked eye, your golden. If you can not, you can either use your spotter scope or binoculars to find Polaris and can see the laser that way.
Thanks,
Mark
--------------------
Meade LX50 8"SCT
Magellan II autofinder
WO 1.25" binoviewer with 3-in-1 Sieberts OCA
Marcus Luden Intes Micro 703 Maksutov 7"
Meade LXD55 GEM mount
Syracuse, NY
Edited by osteomark (09/05/08 09:37 PM)
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1744
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Did you do a "Fine Align" on Polaris, or just a rough align?
Just curious.
Yes, all of these little things add up. Keep everything tight, do a 3 star alignment (if you haven't eliminated Cone Error manually by shimming the OTA) and use the up and right buttons to approach stars. Consistencey is the key.
The "Right" and "Left" buttons control the Right Ascencion motor. Pushing the right button moves the mount AHEAD of the current location (West) in RA, and pushing the left button moves the mount BACK or East of the current object.
Now this might or might not correspond to your eyepiece. Lots of variables. The position of the Diagonal in relationship to the DEC Shaft alignment, whether the telescope reverses the image or inverts it... Too many variables.. I have been observing 30 years and the only way I can tell which way is NSEW is to move the telescope in each axis.
And it gets worse. In my LXD55, when I am viewing targets on the east side of zenith, I puse the Up button to move the scope north.. But when you change to the other side, the Up button will move the mount SOUTH... LOL..
Now my LXD750 lets you sway the way the button behaves, but not the LXD55 I don't think.
So, not always easy to remember which way things will move because when you start twisgint the diagonal, it gets very confusiong.. I genarally just use trial and error.
Good luck..
--------------------
Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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Zebra24601
Postmaster
Reged: 10/09/05
Posts: 7432
Loc: San Gabriel Valley, CA 91770
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No, the lxd55 also has an option for reversing the button directions.
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Zebra24601
Meade 8" SCT w/UHTC * Celestron 100ED * Celestron C11 * Barska 15x70 binoculars
Meade LXD55 mount * Orion Sirius goto mount * Bushnell Voyager 4.5" Compact Reflector
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 1744
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Ok.. Good. My mistake. I figured it might be in there somewhere but I dislike the Autostar handset because I can never easil find what I am looking for. But it is present in some other handsets so it doesn't surprise me that it is in there somewhere.
--------------------
Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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