LX200GPS scope

 

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LX200GPS Specific Issues--
Mount, Optics, Focuser, Misc.

 

MAPUG-Astronomy Topical Archive     AstroDesigns    MAPUG-Astronomy.net
Autostar Hand Controller

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GPS AutoStar GPS photos 
GPS Firmware (v3.0i) Posted (also link for future updates as they are available from Meade) 
DVD--"A Beginner's Guide to the Meade LX200GPS" --outside link 
GPS Tips Source--outside link 
14" Base Casting Beefed Up? 
Peterson EZ Clutch kit on a 14" LX200GPS -- 4 parts 
Scope Certification by Independent Company 
Accurate Time Requirement? 
GPS Alignment Stars Not in FOV 
GPS Accessory Bolt Holes Specs & Tripod/Wedge Mounting Bolts (same as Classic?) 
Schematic Diagrams for GPS  --on 'Battery-p2' page 
Reconnecting Connectors 
GPS Owners Manual-- PDF Download --linked to Meade Contact page 
Other On-Line GPS Owners Manuals-- pdf or web-version 
Worth Upgrading from Classic? 
Checklist for Inital Start-Up and After 
Avoiding Hitting the Hard Stops 
Link to Yahoo GPS Discussion Group 
Control Panel Orientation 
GPS Only Runs on 12v 
Powering the GPS 
Focuser Speed Selection Change 
Focus Lock Adjustment 
Microfocuser Step Size? 
Centering the LX200GPS Microfocuser 
Review: UHTC Enhanced Coating Group vs. Standard Coatings --linked to outside site 
UHTC Coatings Equivalent to Classic Multi-Coatings? --3 parts 
GPS: RS232 to USB Possible? 
RS-232 Cable - GPS same as Classic? 
GPS Interface Cable Diagram --outside link 
External Antenna for GPS Scopes in a Dome? 
GPS Loses Dates! 
Does GPS Internal Battery Holds Ephemeris Data? 
GPS RA Motor Stalled in East Direction --2 parts 
GPS & GEG (Giant EasyGuider) --2 parts 
Optical-Mechanical Alignment 
Going to 2" Diagonal Worth It Visually Or Not? 
Is SMT Worth It? --3 parts 
Meade Dew Shield on GPS Models? 
GPS Mirror Lock Like Classic?
Adjust Guide Rate Feature? 
How to Calibrate Motor on GPS? 
Parking the GPS Scope 

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Subject: LX200GPS Firmware Updates URL   Top

From: Dick, Date: Dec 2004

For those folks with LX200GPS models, Meade posted updated firmware (v3.0i) on their site:
  <http://www.meade.com/support/auto.html> Note: this is also the link for future updates.

3.0i seems to correct the major problems with 3.0d (Polar Park being the worst) while retaining its many improvements over the pre-3.0 series.

They also posted v33Ef for the 497 Autostars, too.

rule

Subject:14" Base Casting Beefed Up?   Top

From: Doc G, Date: Nov 2003

I have just had a long phone conversation with Pete Peterson about the 14" GPS scope. He is a fine gentleman and I trust his judgment.

He tells me that the base casting for the 14" scope has indeed been beefed up from that used in the smaller scopes. Additionally there are some differences in the drive mechanism that he considers a definite improvement over the smaller versions of the GPS scope. Both he and Dr. Sherrod have the 14" scope and are very enthusiastic about it. It has apparently had very few breakdowns and a better record of repair when necessary than the smaller scopes.

His statement is that the 14" GPS is improved enough over the smaller LX scopes both GPS and classic that it should really be called an LX300 because of the design changes. It is, he says, the best scope that Meade has ever made in the LX line. I hope this information reflects reality about the 14" GPS scope. I trust it does. His is back to Meade at this time for a repair of the electronics.

I would conclude, from this conversation, that the 14" GPS scope is the one to get if the size and price are suitable.

rule

Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 1 of 4

From: Robert Darlington <bob@pihkal.com> Date: Jun 2004

I just finished installing a Peterson Engineering "EZ Clutch Kit" on my
14" scope. I took photos of just about every step along the way if
anybody cares to take a look. The kit was $29.99 and includes an hex
wrench (Allen key), pack of grease, cork ring, and instructions. It took
about 1 hour to degrease and install. The instructions were excellent.

Pics: <http://www.pihkal.com/gallery/view_album.php?set_albumName=EZ_CLUTCH>

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Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 2

From: Dale Chatham <dale@chatham.org>

I, too, just installed this kit on a new LX200 14" myself.. I was a bit skeptical about its utility, but since it was only $29.95, I figured "what the heck". All I can say after installing it is "wow!". Although I didn't particularly think that the amount of torque to get the original clutch engaged was excessive, the amount with the new one is very small. I'm impressed. I highly recommend it!

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Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 3

From: <Rick.Woods@AD.STATE.AZ.US>

The EZ clutch is not only cheap and easy to install, it's pretty much a must-have for the 14". Pete went into great detail somewhere about it, but the short version is the dec clutch screw will end up stripping out, especially on the heavy 14", and there's no easy way to fix it when this happens like there is on the smaller scopes. I was pleased with mine. It does exactly what it claims: cuts the amount of torque required to hold the dec adjustment just about in half.

VERY cheap insurance against what would be a lousy, inconvenient, and possibly very expensive failure.

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Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 4 of 4

From: Pearson <P26@cox.net>

Actually I'm flattered by Bob Darlington's being so impressed with the clutch upgrade that he went to the trouble of photographing it and posting it.

There is a fine line here regarding intellectual property as this upgrade solution isn't obvious. Where others focused on getting a bigger clutch knob I'd always been concerned regarding the minimal thread tapped in the scope's aluminum trunnion. Development of the EZ Clutch took about 2 months of effort, and since the instructions are revised whenever someone has to ask us a question, the instructions have been revised about 20 times.

Just about all of our upgrade instructions incorporate extra non-upgrade associated tune-ups and adjustments in the area being worked on. And many times the optimal techniques that we have developed for the upgrade installation are not intuitive. This is why the installation instructions are considered to be a major part of the kit's value added, and why I've asked folks not to publish the instructions.

In Bob's case, all he has is a series of un-annotated photos, and he hasn't documented any special procedures. So I'm not going to sweat it. Recently someone else got real excited about another of our upgrade kits and posted a series of extremely detailed annotated step by step photos that did disseminate our intellectual property. He flattered us by putting a huge amount of effort into his posting, and was shocked when I asked him to pull the posting.

We do have sample instructions posted for our most complex upgrade - the Buck's 14" Gears.
< http://www.petersonengineering.com/SkyDiv/14-inch_sample.htm> But because of the intellectual property situation we never transmit full instructions in digital form.

Upgrades for Meade's LX200GPS telescope is probably the smallest niche market in the world. I make my living from the engineering side of the business designing & fabricating robotic machinery. The Sky Division is an offshoot of my personal need for things that weren't commercially available and were needed on my personal scope. I originally figured that since we had some pretty sophisticated CNC mills, lathes and machine centers available, and since I'd gone to the trouble of designing & making an EyeOpener for myself, I might as well make it available to fellow amateurs. Doc G was one of my mentors on development of the original EyeOpener.

I do thank you folks for being sensitive to the intellectual property thing. And for the kind words regarding our upgrade.

rule

Subject: Scope Certification by Independent Company   Top

From: Don Tabbutt <dona_ttabbutt.com> Date: May 2003

Arkansas Sky Observatory will certify the entire scope for a fairly hefty fee. Even so, some members of the LX200 GPS Yahoo group have their scopes shipped directly there when they order them.

Check it out here: <http://www.arksky.org/> ...and click on "Services".

rule

Subject: LX200GPS-- Accurate Time Requirement? --part 1 of 2   Top

From: Kevin Wigell <kwemaila_ttwcny.rr.com> Date: Jun 2003

Terry wrote:
> I am planning on letting the scope take a GPS fix at the beginning of every
> observing session primarily to have the time set accurately at the beginning
> of each night. I don't know how accurate the clock is on the scope, but if
> it is no better than clocks in computers, the time will need to be updated
> every night. I am thinking that this would be an easy, foolproof way to do it.

Terry, unlike the LX200 Classic, the LX200GPS doesn't keep time when it's turned off. So if you can't get a GPS fix, you will have to set the time manually each time you turn it on. That is what we have to do with our club 16" GPS scope, which is inside a dome and can't get a GPS fix. On the other hand, accurate time is not important to either accurate pointing or tracking. Anything within a few minutes of the correct time is fine.

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Terry wrote:
> Since "GoTo-ing," longitude, and time are all related, if the time is only
> good to a few minutes, the telescope can only point accurately if it thinks
> it is at a different longitude than the actual, correct? If that's the
> case, what happens the next night when the time is entered only to an
> accuracy of a few minutes? Is the scope forced to think it is at yet a
> different longitude? So, if your second night's time is right on, you still
> won't get good pointing, since the scope thinks it's at the wrong longitude,
> from LAST night's time inaccuracy. Is this not correct?
>
> It would seem to me to keep all three of these factors as consistently
> linked as possible, the time would have to be known by the scope as
> accurately as possible. An error of one minute of time can cause an error
> of up to 15 arc minutes in pointing.

Accurate pointing is not primarily a function of the correct time, date, or location. These factors are needed to calculate where your local horizon is, and how much atmospheric refraction to correct for.

Accurate pointing (or GoTo-ing) is mainly a function of how good your 1- or 2-star alignment is. You can easily confirm this with a simple experiment. Deliberately set your time off by 30 minutes. This is not enough to really affect your horizon calculation except for very low objects. Then do your star alignment as usual. You'll find your scope GOTO's just fine. If the time were that important, you'd miss by a mile. The only problem with having the time, date, or location off is that some objects may be reported as being below the horizon when they are not, and the correction for atmospheric refraction will be off. But if you are "close" on location and time (and date of course), your pointing accuracy will be very good as long as you have done a quality star alignment. And the key to that is to use a reticule eyepiece.

Oh, and very inaccurate dates or times will cause the internal calculations of the positions of the planets, and especially the moon, to be incorrect.

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Subject: LX200GPS-- Accurate Time Requirement? --part 2 of 2    Top

From: Bill Keicher <wekeichera_tattbi.com>

If you want to open loop acquire and track satellites, you need fresh satellite ephemerides, good location information and precise time. Low earth orbiting satellites can move at a few degrees/second.

rule

Subject: GPS Alignment Stars Not in FOV

From: Richard Seymour <rseymoura_twolfenet.com> Date: July 2005

>When I'm doing the automatic alignment process on my LX200 GPS 10" ,
> the alignment stars are nowhere near being in my finderscope field of view.
> I'm 5-10 degrees off. Smart Mount is turned off. Why is this happening?

First, do a Calibrate Sensors. That tells the Autostar your local magnetic deviation from true north.

Then, with recent firmwares, do *three* AutoAligns (this can take 3 nights, or be squeezed into one 15 minute session). The Autostar will learn, from your centering of alignment stars, how to tweak the level sensor and magnetic readings and the initial slews will improve.

My own drops from a 5 degree error down to less than 1/4 degree, i.e. within the FOV of the 26mm eyepiece.

You could take either of two courses of action:

(a) simply -ignore- it, slew to center the stars, and continue with the evening... the actual GoTO's should be good. (and by the 3rd night, the problem will have gone away... unless you do something that destroys the accumulated learning, such as a 2nd Cal Sensors)

(b) use Two Star alignment instead of Auto. When doing so, first -accurately- point the OTA due true north, and level the tripod head and OTA before powering up. You can achieve initial slews that will only be limited by the accuracy of your north-pointing. (I use a landmark a few blocks away, and can achieve sub-1/4 degree slews).

rule

Subject: LX200GPS Accessory Bolt Holes Specs & Tripod Mounting Holes

From: Jim Henson <jimha_tbga.com> Date: April 2003

The accessory screws on the OTA are 8-32, just like the LX200 Classic. The tripod & wedge mounting bolts and spacing is also the same as the Classic.

rule

Subject: LX200 GPS-- Reconnecting Connectors    Top

From: Kevin Hobbs <ve3kha_tcogeco.ca>

-----Original Message-----
From: M Whiteman
I got a new LX200 GPS 12" and have run into a little problem. When I was removing the long centre 1/2' dia. screw, it seemed that it was tight a couple of turns before it released. No problem noted after that. I have not used it since.

I decided today to remove the bottom plate and see if I could see any problems. It turned out the inner nut with the two holes in it was loose. It had rotated and since there was wiring that also fed through the nut to the other parts of the scope, it unplugged the connectors from the main circuit board on the front panel. I do not know where each connector goes. The nut has been fixed.

There are one 9 pin, two 6 pin and one 2 pin. The nine pin was easy since there was an open 9 pin connector for it. I do not know where the two 6 pin go and there are 2 available plugs. The 2 pin has 2 possible plugs to fit into.
-----End of Original Message-----

-The nine pin is obvious.
-The six pin with ferrite bead on the wire bundle goes to the mating connector nearest the power plug.
-Only one place left for the other 6 pin.

Editor's note: see photos above.

rule

Subject: LX200: Worth upgrading to GPS? --part 1 of 2     Top

From: Roger Hamlett <ttelmaha_tntlworld.com> Date: Oct 2002

----- Original Message -----
From: Alan Voetsch
> > I'm considering selling my 10" Classic LX200 and getting the 10" GPS version.
> > What are peoples thoughts on this?
>
> I won't comment on the GPS part of this equation.
> The other advantages that I see in the new over the
> classic are mainly of benefit to those doing
> astrophotography. The mirror lock and the microfocuser
> are features I would love to have. These are items you
> can live without for mostly visual use.

However the 'downside' for imaging, is that the existing focuser on the GPS, does not provide properly controllable positioning (even relative positioning). This means if you want to autofocus, you'll end up buying either a third party focuser like the NGF-S, or an upgrade to the existing focuser, which puts you in a similar position to 'classic' owners. On both the 10", and 12" 'classic,' mirror lock is easy to provide, so the advantage here is very small...

The biggest question is how good one's existing optics are. If you are happy with them, it is the 'long term' support, 12v operation, and the UHTC coatings, that probably represent the biggest advantages to the GPS.

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Subject: LX200: Worth upgrading to GPS? --part 2 of 2     Top

Bill Arnet<billa_tnineplanets.org> writes:

> Can anyone comment on the relative merits of the
> mechanical aspects of the GPS vs. Classic LX200s?

The fork and drive base, to me, appear just as good. As far as steadiness, I don't note any improvement, however--excellent on the 8, good on the 10, just OK on the 12 and ? on the 14. The dec seems considerably smoother than most classics (those without ball-bearings in the dec). The gearing, the transfer gearing, in RA is worse according to what I'm told (I haven't torn one down yet). Small nylon gears in a position where high torque is possible. I am told by Clay Sherrod that Meade is taking steps to improve this situation now, however. Don't like the dec lock at all--it's a considerable step _back_ from that on the classic, appearing similar to that on the LX90. Works fine on an 8, but has problems locking firmly with the larger scopes; that's why various entrepreneurs are selling "dec-fix" kits already.

If you have an LX200 that's working well, I'd hold off. Meade is still fixing problems with the GPS. There was a brand-new out of the box LX200 GPS 12 on the field at the recent Peach State StarGaze. The new owner could not get it to align. Period. Operator error? Maybe. Software? Maybe. Hardware? Maybe.

Enjoy your "classic" 200 for a while longer...maybe 6 months or so...then come back. I would not upgrade even then unless you want to go to a larger (or smaller) aperture. The GPS is nice, but it just doesn't offer enough advantages over the classic to be worth the trouble, in my opinion.

rule

Subject: LX200GPS Checklist for First Set-Up & After      Top

From: Rod Mollise <RMOLLISEa_taol.com>

The good folks over on the Yahoo LX200GPS group have created a Checklist for first time set-up and quality check, and then steps for regular set-up. Goto: <http://groups.yahoo.com/group/lx200gps/>. Go to the "Files" section (Note: you must first join the group before you can access the Files), and look for "LX200GPS Start-Up Checklist.pdf." There are several other very useful files for the new GPS owner too, including tips, etc.

rule

Subject: Avoiding Hitting the Hard Stops    Top

From: Don Tabbutt <don@tabbutt.com> Date: Sep 2003

-------Original Message-------
From: Christian Molnar

The scope is, as others have stated, about inbetween hard stops, but it starts one way, goes about 150 degrees, then stops, but instead of changing direction, it continues the same way. This puts it almost at its hard stop when it believes it is in home position. SO when it goes to Arcturus, it hits the hard stop.

So if anyone has any suggestions, please shoot. Right now I am thinking it may be a dirty sensor?
-----End of Original Message-----

It sounds like one of the Home sensors is inoperative for some reason. It could have a broken or loose wire, or more likely, has been fouled with grease or bent and simply needs cleaning or straightening. Pictures are here:

<http://rseymour.home.wolfenet.com/LX200guts.html>

and here's what Pete Peterson found when he fixed his:
> I removed the base bottom plate, and eyeballed the position
> sensors. They consist of 2 pairs of photo emitter/detectors
> on a small 1" x 2" pc board. The clear LEDs are obviously the
> emitters, and they're oriented so that it's facing you if the base is
> inverted. About 1/4" away facing them is a black transistor shaped
> receiver. Each pair is at a different height and the light beams are broken by
> the respective split rings that control the 600 or so of rotation.
> In my case, the lower emitter was not standing erect off of the PC
> board, but was bent forward so that the light beam wasn't directed at
> the detector. The bottom part of the emitter was covered with black
> grease, and some of the grease was on the working side, blocking
> light. I cleaned it up, straightened it up, and wiped the excess
> grease off of the bottom of the split ring. And then I tested
> through full rotation stop to stop to insure that something wasn't
> going to clobber the LED again. It ran clear, so I closed `er up,
> fired her up, and got a good alignment. Problem fixed.

In any case, a first troubleshooting step is to turn off the Home Sensors: Select Item > Setup > Telescope > Home Sensors > Use Sensors > Off. With them off, the telescope will not attempt to find Home (useless in Polar anyway).

With the telescope off, on a wedge, with Dec set at zero, and *the eyepiece end* centered over the power panel with *the eyepiece end* pointed north (corrector pointed south), release the RA lock and rotate it west (counterclockwise) until it hits the hard stop. Now rotate it east until *the eyepiece end is* just pointed north again and centered over the power panel (corrector pointed south), and lock the RA. Power up and align normally, and the scope should never hit a hard stop.

Also, be sure your friend is actually in Polar mode. Finding the Home sensors is not normally part of a routine polar alignment (One Star, Two Star, or Easy) unless he chooses Align on Home. That last choice is really there for a "lost" remote telescope that got powered down (for whatever reason) in some position other than Park.

rule

Subject: GPS Yahoo Group     Top

From: Wade <sdwesta_tmchsi.com>

The LX200GPS group has over 1400 members already:<http://groups.yahoo.com/group/lx200gps//>

Try the LX200GPS group. Read the Archives, Files and Databases, you'll find a wealth of info already in there. I look forward to the almost 50 emails a day I get on that group.

I've already downloaded the new AS II v. 3.33 and build 1.1a firmware. There are still a lot of issues. After resetting and "taking out the trash" (one of the options on the v3.33) and THEN loading 1.1a to my handbox, did I get it to do any GOTO.

Using my 26mm Meade "standard issue" eyepiece, I was able to find the two bright alignment stars (Sirius and Alioth) in this eyepiece through the hazy sky, and did a GOTO to Jupiter and it was in the eyepiece. What a rush that was!!

I've since Calibrated Sensors and Trained Drives, and now it doesn't even come close!! I can only believe that the light overcast resulted in my seeing only the brightest stars, which allowed me to pick the correct ones for the initial alignment.

I'm not too concerned about this scope, I think the mechanical and electronic problems will get ironed out. Meade has been pretty responsive so far. My biggest concern is the way Meade seems to label each tube differently, I'm not sure what they are doing with the optics and then they come out with a new coating material for the mirror just a week after I received mine! It was my own fault for jumping in right on the new release, I guess. I received mine on March 12, and it doesn't even say it has EMC coatings on the tube or on the box. It's hard to know when this thing was really put together.

rule

Subject: LX200GPS Control Panel Orientation    Top

From: William Drelling <gatorchasera_tearthlink.net>

The manual alignment is the same as the previous version of the LX200 except that the control panel of the GPS version must face south vice north, i.e., be on the south side of the tripod.

rule

Subject: GPS Only 12v Power Use? -- part 1 of 2

From: John Alfredo <john.alfredoa_ttranscore.com>

I recently purchased a new 10" LX200GPS and have seen numerous postings about 18V and 12V-18V convertors and was confused, so I called Meade tech support and they told me that, although older LX200's ran on 18V, I should _NOT_ run my new LX200GPS on anything other than 12V.

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Subject: GPS Only 12v Power Use? -- part 2 of 2    Top

From: Roger Hamlett <ttelmaha_tntlworld.com>

Dead right. This was one of the redesigns on the new scope, to get away from exactly the problem being discussed. Use of 18v, applies _only_ to the LX200 'classic'.

rule

Subject: Powering the GPS     Top

From: James Fisher <jfisher857a_tjuno.com> Date: Jan 2003

Maybe I can help you with your power concerns and the 8" LX200GPS. On another users group dedicated to the GPS version of scope, virtually no one uses the internal batteries. The scope responds best to a voltage of 13.6 to 15 when slewing and working with a load. The 8 C cell batteries at most will only put out 12 volts, add cold weather, and it will be less. Don't get me wrong , the internal batteries will work, but the amount of time they will work makes them a very expensive way to operate the scope- in the field.

Most owners, including myself, use a 12v. 26 Amp Hr. Jumpstart Battery. They typically put out 13.5 volts fully charged and will run the LX200GPS 8" several nights before charging is needed. I use this battery even though A/C power is available. I don't have to worry about the power company interrupting my viewing session or surges or power spikes or electrocution. However, do not run any dew equipment from the same battery source.
Editors note:
for additional battery power ideas see this topic.

I have two Jumpstart batteries, one for the scope and one for the accessories. Also do not try and use rechargeable C cell batteries, their power curve is horrible for use in this scope especially in cold temps. Many have reported using these Jumpstart batteries for over three years on various scopes, and they still take a charge fine.

We use the battery compartments to hold counter weights to balance the scope in polar mounted (wedge) situations. Remember, if you feed your scope the proper diet ( 13.6v to 15v. ) to keep it happy.

rule

Subject: LX200 GPS Focuser Speed Selection Change  Top

From: Tom Mote <pytoma_ttexas.net> Date: Apr 2003

After I sent the message about using the JMI hand paddle with my LX200GPS, I did some more testing and, to my dismay, found that I could not control the focus speed while using the Meade paddle. The Meade microfocuser speed selection had worked perfectly just before I updated the firmware from version 1.2A to 1.6B but now, no matter what focus speed I attempted to select, it always was "FAST," i.e., the speed which I reported took 11 seconds to move from either limit to the middle of the focus range. I phoned Meade and the technician had not heard of any problems with the new version but suggested that, instead of using the numeric keys, as I had been doing, I try using the scroll up and scroll down keys. IT WORKED LIKE A CHARM! the moral, if any, is that when Meade comes out with a firmware update, they make changes and it may be many months before there is any documentation for the user.

rule

Subject: GPS Focus Lock Adjustment  Top

From: John Mahony

> I just received my 8" LX200GPS, and I am concerned that there is a problem
> with the focus lock, in that it does not seem to lock anything. With the
> focus lock knob turned to the lock position (as tight as I feel
> comfortable setting it, and tighter than I expected would be
> necessary), I find very little difference in effort in turning the
> focus knob. There is perhaps the slightest bit difference in turning
> torque, although I had to go back and forth between the locked and
> unlocked positions to be able to notice this at all. And the focus
> changes either way, although there does appear to be a slight amount
> of backlash in the "locked" position. I want to emphasize that I am
> not forcing the focus knob at all - it turns very easily even when fully locked.

Buck Harley posted some info on a common problem with the lock in the files section of the Yahoo Meade_Uncensored group. Sounds like it may be what you're experiencing:

For those that can turn there mirror lock stop to stop, it is made the way I thought it was and is easy to adjust.

1. first turn the knob all the way to the unlock position

2. then remove the 3 cap screws remove the knob assy by tilting it slightly

3. after you have it out you will be able to see the 8" steel gear... that will have about 1" of it with no teeth this the stops.

4. you will have to take your finger and push down on the gear until the part with no teeth on the gear is pass the hole towards focus knob..

5. reinstall the knob and now your lock will lock and unlock do not worry if you cannot turn it 10 turns just turn until you feel resistance… you will be home Sweet ..

BTW Meade Sent the Allen wrenches for this job make sure they are pushed all the way in the alum cap screws as not to strip or mar them. He also posted a zip file there with pictures of the insides of the scope, but it may be just the drives- don't know if it includes the lock.

rule

Subject: GPS Microfocuser Step Size?    Top

From: Dick <autostaretxa_tmindspring.com> Date: Apr 2005

> Does anyone know what the step size is for the Meade microfocuser?

The microfocuser on the LX200GPS is not a stepper motor. The Meade microfocuser uses a typical inexpensive DC "analog" motor. Such motors don't have a clearly defined "step size" (they can stop anywhere, they call fall backwards a bit, etc.). They do, however, tend to stop with an armature pole aligned more or less (there's the "lack of STEP" again) centered with relation to one of the field magnet poles.

The Meade driving circuit for the focuser is pulse width modulated (PWM) at nearly 12v (probably within a volt of full battery voltage). They're not trying for "stepping", merely "delivered energy over time" (the area under the PWM's steps per second).

rule

Subject: Centering the LX200GPS Microfocuser    Top

From: Tom Mote <pytoma_ttexas.net> Date: Apr 2003

To answer my own question: has anyone come up with a quick and/or reliable method for setting the Microfocuser to the center of its range? The answer: you simply run the Microfocuser in and out until you have the "knobbed set screw" just even with the edge of the slot in the outer barrel of the device. This gives you approximately a quarter of an inch (6mm) available travel either in or out from that point.

rule

Subject: UHTC Coatings Equivalent to Classic Multi-Coatings? --part 1 of 3  Top

From: Roger Hamlett <ttelmaha_tntlworld.com> Date: Dec 2002

----- Original Message -----
From: Kevin Wigell
> On another list in which I participate (APML), there is a thread
> floating around right now in which some are speculating that the
> new UHTC coatings are roughly equivalent to the classic multi-
> coatings, and that the new "standard" coatings are actually a
> downgrade from the classic coatings.
>
> Does anyone here have any evidence or comments on this one way
> or the other?

The point, is not that the standard coatings have been downgraded. The new coatings do what is claimed, relative to the older Meade coatings. What has become plain though, is that compared to the Celestron coatings, the difference is not so large. It appears that the Celestron 'Starbright' coatings, have been significantly better than the older Meade offerings for some time, but this was not being pushed in the same aggressive way. Meade have now overtaken Celestron, by a small amount (the new Meade coatings appear to give a flatter response curve than the Celestron offering, with better response at the red end of the spectrum, but very fractionally less response in the green).

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Subject: UHTC Coatings Equivalent to Classic Multi-Coatings? --part 2  Top

From: Radu Corlan <rcorlana_tpcnet.ro>

Roger Hamlett wrote:
> > Oh, but the standard coatings have been downgraded; If you look into any
> > recent Meade advertisement, under 'specifications', it tells what the
> > 'Meade standard coatings' are: MgF on corrector, standard Al on mirrors -
> > that's obviously not what EMC was.
> >
> > And all the graphs and improvement claims use the 'standard' coatings as
> > baseline, not the EMC.
> The comparisons on the web, have all been against the EMC coatings, and give
> the claimed improvements...

I don't argue with that.

> > I have no way of telling how the UHTC are comparing to the old EMC, but
> > it's clear that Meade's advertisement doesn't compare UHTC with EMC.
> How is this 'clear'?.

Well, it's 'clear' because the baseline graph is labeled 'standard', not EMC, and because the specifications list 'standard' as MgF, which is not multi-coated.

The corrector plate coating doesn't contribute that much to throughput anyway (With MgF, the reflection coefficient is ~1.5%, so even going to a 'perfect' coating will only improve throughput by 3% max; the difference from EMC, which is multi-coat should be even smaller);

However, reducing the reflections from the back of the corrector 2-3 times will significantly reduce multiple reflections and scattered light and improve contrast; this is the main reason you want good coatings on the corrector, not throughput

Big improvements in thoughput are obtained by changing the mirror coatings; The 'standard' Al+SiO mirror coat is only 92% reflective at visible wavelengths, and can be improved to >98%. My guess is that here is the principal difference between EMC coatings and UHTC.

To reconcile all information, this is what we have: 'classic (EMC)': multi-coated corrector, standard Al mirrors new non-UHTC : MgF corrector, standard Al mirrors UHTC : multi-coated corrector, enhanced Al mirrors

This will explain the difference in thoughput between EMC and UHTC; but also mean that the 'standard' coatings have been downgraded - Not so much from the throughput point of view, but from the contrast/multiple reflection point of view.

Anybody made a comparison between non-UHTC new scopes and 'classicals'? That would be the missing test to prove/disprove my theory.

-----------------------------------------------------------------------

Subject: UHTC Coatings Equivalent to Classic Multi-Coatings? --part 3 of 3  Top

From: Don Tabbutt <dona_ttabbutt.com>

Read Dr. Clay Sherrod's review here: <http://arksky.org/uhtc_compare.htm>

In a nutshell, UHTC performs as Meade claims vs. EMC coatings.

rule

Subject: GPS: RS232 to USB Possible? --part 1 of 2      Top

From: Bob Benamati <bobbenamatia_tcomcast.net> Date: Jan 2003

----- Original Message -----
From: Susan-- Does the LX200GPS scope interface cable at the computer have to be RS232 to the Com port or is it possible to interface using USB? I suppose one gets an RS232 to USB converter if it exists?
----- End of Original Message -----

Meade makes a USB-RS232 interface now..... just saw it at OPT's website while shopping for something else. Works for "Classic LX200s, too!

-------------------------------------------------------------------

Subject: GPS: RS232 to USB Possible? --part 2 of 2

From: Don Tabbutt <dona_ttabbutt.com>

Autostar interfaces perfectly via USB using the Belkin USB to Serial adapter F5U109, $29.99 at Circuit City. It's marketed as a PDA adapter, but will work with any serial device. Never misses a beat. I also use the Belkin 4-port USB Mini-Hub with the laptop, a tiny little thing half the size of a deck of cards.

I have five of them used as follows:

  • LX200 Classic to laptop.
  • ETX125EC Autostar to laptop.
  • RoboFocus to laptop.
  • 208XT to laptop.
  • Uninterruptible Power Supply to desktop (for automatic shutdown in case of power failure).

rule

Subject: RS-232 Cable - GPS same as Classic?      Top

From: Bill Dougherty <bd5572a_tyahoo.com> Date: Dec 2003

Luigi Fontana wrote:
Does someone know if the RS-232 cable for the GPS and the Classic LX200 are exactly the same?

The Meade 9-pin RS-232 to LX200 cable that I bought for my Classic works fine with my GPS scope.

rule

Subject: External Antenna for GPS Scopes in a Dome? --part 1 of 3     Top

From: Mohammad Odeh <odeha_tjas.org.jo> Date: Mar 2003

Kevin Wigell wrote:
> My club recently installed a 16" GPS LX200 in a dome. The dome completely blocks the GPS
satellite signals from getting to the antenna on the scope. Of course, the location never changes,
so that is not a big deal. But due to the lack of a clock chip in the GPS models, we have to reset the
time in the scope each time we turn it on. A minor inconvenience, to be sure.
>
> But, we were wondering if anyone knows of a way to connect an external antenna to the
scope-mounted antenna so that the GPS signals will get through? If there is no way to directly
connect an external antenna to the scope, what about some sort of "repeater" that would
re-broadcast the GPS signals inside the dome? <

This antenna should solve your problem:
   <http://www.gpscentral.ca/accessories/mmwide.htm>

-------------------------------------------------------------

Subject: External Antenna for GPS Scopes in a Dome? --part 2

From: David Morris <dmorrisa_tuniv.llu.edu>

I haven't posted for so long I hope this works, but there is a place you can get a remote antenna that should work with your 16" scope in a dome. Look at:
   <http://www.gpsoutfitters.com/> and check out the Vortech Antenna System. I think it is around $100 but might be worth it for some. One person reported he had one and it worked very well.

--------------------------------------------------------------

Subject: External Antenna for GPS Scopes in a Dome? --part 3 of 3    Top

From: Radu Corlan <rcorlana_tpcnet.ro>

> However, on a good note, it looks as if I could open the casing and remove
> the antenna. Perhaps, with a couple of lengths of wire, I could mount the
> antenna outside and leave the rest of the unit inside, if I needed to. Don't
> quite know how that will affect signal strength, though! Perhaps the same
> can be done with the GPS scopes, with the addition of some type of signal
> booster? At what cost, though?

You have to use special coax that has low losses at 2G; Most of the cost of remote gps antennas comes from the cable. Even with good cable, if you have to reach more than 1-2 meters, you will have to use an active antenna.

rule

Subject: GPS Loses Dates!     Top

From: Bill McCarthy <willymac1a_tbtinternet.com> Date: Apr 2002

I would have thought with such sophistication that is built into the GPS scopes that there would have been a small clock panel incorporated somewhere that enabled you select local time, hour angle, GMT, UT etc. There is certainly plenty of room on the forks.

Rod Mollise wrote:
>I find it reasonably annoying with the other Autostars...and yes, it would
>be laughably easy for Meade to "fix" this. I suppose it's not a huge thing
>if you're getting a GPS fix every time with the new scopes, though.

rule

Subject: Does GPS Internal Battery Holds Ephemeris Data?

From: autostaretx <autostaretxa_tmindspring.com> Date: July 2005

R Hamlett wrote:
> The battery, allows the GPS, to hold it's ephemeris data, not just the location.

Yes, I should have mentioned that; however with the Sony chipset Meade uses (CDX2931R-9 in mine, I think they've upgraded to the 2932 in newer scopes) is able to achieve a full fix in under two minutes, even from a cold, no-ephemeris, no-almanac condition. (the data sheet says 58 seconds)

I have seen that to be true, I've run multiple tests of unplugging my LX200GPS' battery to force the GPS receiver to its dead-cold state (random time/date, Tokyo's Lat/Long).

rule

Subject: LX200GPS RA Motor Stalled in East Direction? --part 1 of 2    Top

From: Roger Hamlett <ttelmaha_tntlworld.com>

McPherson Graham <graham.mcphersona_tavecia.com> wrote:
I have a 12" GPS system which has worked perfectly until last week when the dew heater control (BC&F) pulled from its fork arm velcro and landed on the wedge (permanent metal pier into ground) and I guess there was an earth from the tape connector part as a nice tiny blue spark popped and the dew heater failed. At the time both the LX and the dew controller were running off the same 12V battery supply.

From that point the LX complained that the RA motor had stalled whenever an "East" motion was required and although N,S and W work from the key pad I have no joy with E (rightmost key) it just moaned that the motor had stalled.

I replaced the fuse on the dew controller (2Amp) and gave it its own battery (it works fine) and recharged the one for the LX - (in case it was the poorly charged battery trick). To no avail.

Now I can turn on the scope go through the polar one star align and the motors slew to Polaris (so good so far) but after I adjust the mount and press enter - I get the message "motor stalled" this is most frustrating as I have W but no East. I can only assume that this is 99.9 % going to be an electrical problem given the fuse blowing coincidental timing. I don't have a problem having a poke in the guts of it but I have no idea where to start - does anybody have any ideas?
--------End of Quote--------

Ouch...
We can rule quite a few things out. Power is getting to the motor controller (since otherwise it would not move W). The message, is saying that when it signals the motor to move E, no pulses are being seen from the movement detector. Fortunately, we can rule out a failure in this detector, since it is the same system that detects motion in the opposite direction (all that changes is the 'timing' of the two signals). Similarly, problems with the motor or gearbox, can largely be ruled out, since these work in the other direction. There would seem to be two likely possible failures. The first is the motor driver chip itself. The second, is the op-amp circuitry feeding this chip (more fragile). Though both these parts are partially 'common', to the other direction, they are being driven the other 'way', and different internal transistors are being used. The components are a L2724 driver, and parts of two LM324 quad op-amps. These are U15, U16, and U17. Fortunately, none of these parts is expensive, and are readily available in the UK (in fact the L2724, is easier to get over here, than in the States - I have a quantity, that I will sell to anyone who needs one.

It really is down to how good you are at electronics/soldering. The key with a repair of this sort, is to remember that the board is a lot more valuable than the parts. It is not worth spending a lot of time trying to desolder the old parts, and risking damaging the board. Instead cut the old parts out (for the cost of a few pence for the op-amps, and a couple of pounds for the driver), remove the legs individually, and solder in the new parts. It would be relatively easy with a scope, to identify which part has actually failed. Fortunately the fact it works the other way, rules out a failure further 'inboard', to the main control logic. If you are not into soldering yourself, this board is not the place to experiment. Instead see if there is a local TV repair shop, who will replace the parts for you (though see if you can have a look at the quality of their soldering first - a lot are remarkably bad...).

-------------------------------------------------------

Subject: LX200GPS RA Motor Stalled in East Direction? --part 2 of 2   Top

From: Randy Marsden <jmarsdena_tsan.rr.com>

Graham, based on the symptoms, it sounds like your motor driver has blown. These typically are a circuit usually called an H bridge with the motor as the cross bar and transistors as the four vertical arms. Going one way, current through the H will flow Northwest to Southeast, while for reverse direction, current would flow from Northeast to Southwest, reversing the direction of current through the motor. So what seems to have happened is that one of the four transistors was blown out - the motor would then move in one direction and not the other. So, you need to determine which IC is the motor driver and repair it. Note: it may be a dual motor driver with two complete H-bridges. The part probably costs less than $5.

rule

Subject:10" LX200 GPS & GEG (Giant EasyGuider) --part 1 of 2    Top

From: Roger Hamlett <ttelmaha_tntlworld.com>

----- Original Message -----
From: <adicota_tiwon.com>
> I've got a 10" LX200 GPS and have a GEG (Giant EasyGuider by Lumicon) that I should
> receive in the mail any day now, but I have a concern which came to mind this morning.
> The GEG is designed to mount directly to the rear cell of the scope, but the GPS has
> the new design with the microfocuser. The microfocuser can be removed and
> it looks like the GEG can mount to the rear cell as always, but it doesn't
> appear that the GEG can mount to the scope with the microfocuser in place.

No the GEG will not mount with the microfocuser in place. One of the main 'points' of the GEG, is that it fits to the 3" visual back, to maximize the open aperture. The microfocusers mounts to the same place, and does not offer 3" threads on it's tail.

> This makes the microfocuser useless for GEG photography. Also, the
> effectiveness of the mirror lock is reduced because there is image shift
> when the lock is engaged and without the microfocuser there is no way
> to refocus after engaging the lock.
> Anyone out there already have the GEG with the GPS scope
> who can elaborate on this?
> Has anyone out there begun work on an adapter ring to allow the GEG to
> mount to the working end of the microfocuser? I'd be interested.

This would 'throw away' a lot of the reason for the GEG. The actual 'clear' diameter of the microfocusers is less than that of the main scope, and also since you are shifting the imaging plane further away from the scope, the vignetting caused by the baffle tube will get worse. I'm afraid that if you want the large clear aperture that the GEG gives, you will need to ignore the microfocusers, and possibly consider an alternative solution to most of the mirror shift problems (such as attaching a RoboFocus to the main focussing knob, and letting it compensate in software for the 'focus' shift - though not for the meridian shift).

-----------------------------------------------------

Subject:10" LX200 GPS & GEG --part 2 of 2    Top

From: Doc G

It is not possible to mount the GEG on the new GPS focuser. The focuser takes 2" tubes while the GEG is designed to be threaded directly on the back of the scope with the 80 mm thread. It is not possible to make and adapter which would do what you want to do. Sorry.

rule

Subject: LX200GPS: Going to 2" Diagonal Worth Every Penny Visually Or Not?      Top

From: Don Tabbutt <dona_ttabbutt.com> Date: Jan 2003

Why do you want a 2" diagonal? Do you have any 2" eyepieces? If not, then you don't need a 2" diagonal. Keep in mind Schmidt-Cassegrain telescopes, especially f/10 models like your 8" (and mine), are not designed for wide-field vistas, such as those provided by 2" eyepieces. There's also the problem of the central obstruction caused by the secondary. Unless you're at a pitch black observing site, with your pupils fully dilated, you'll never be able to satisfactorily use a wide-field, low-power eyepiece with your scope (neither can I). Read Al Nagler's article, "Choosing Your Telescope's Magnification", from the May, 1991 issue of Sky & Telescope for a full explanation of this. It's available here:
  <http://www.televue.com/engine/page.asp?ID=140>

Because of where I live, and the extremely rare opportunities for me to get to a really dark site, here's what I did, which I considered a better use of my money than investing it in a top-of-the-line 2" diagonal and expensive 2" eyepiece set which would be used only occasionally:

  1. Got a 1.25" Tele Vue Everbrite ($190) diagonal for use with all of my 1.25" eyepieces. It was like buying a new scope compared to the views I had through the Meade 1.25" diagonal. This is the setup I use 90% of the time.
  2. Got a William Optics Megrez 80mm f/6 refractor ($669) and piggybacked it on the LX200 with Losmandy rings and 3D counterweight set (about $400) for spectacular wide-field views. With a 1.25" Tele Vue 32mm Plossl, I get a 3.3 degree field of view at 15 power that will blow your socks off. Also, it comes with a gorgeous 2" diagonal that would fit into a Schmidt-Cassegrain 2" visual back if necessary. I don't use it in this manner, even when the occasional friend wants me to take a look with his new mega-dollar 2" eyepiece, because...
  3. I got the Meade 2" flip mirror system ($250) for astro-imaging, but it also makes a fine 2" diagonal. The new ones have UHTC coatings, making them even better. Since the mirror can be readily collimated (rare for a diagonal), you can get a nearly perfect setup.

I'm writing this not to discourage you from getting a 2" diagonal, but to give you some idea of the caveats and alternatives for your hard-earned dollar.

rule

Subject: Is SMT Worth It? --part 1 of 3    Top

From: Gene Horr <genehorra_ttexas.net> Date: Jan 2004

Rick Woods wrote:
> Thanks to everyone for the replies. As soon as I clicked "send" I
> realized "duh, use Google!
> But I'd still like to know: Is SMT worthwhile?

Assumint that it works as well as T-point, the answer is "maybe". Remember, it only can correct for repeatable errors. Mirror flop is still going to produce uncorrectable problems assuming that the primary is not locked into place. And with these systems there really isn't an workable way to make all of the corrections perfect.

But it does improve things. If you are having problems now with getting an object on a CCD chip after a slew then it would be worthwhile. If after a slew the object is on the chip just not centered then it is probably not worthwhile.

----------------------------------

Subject: Is SMT Worth It? --part 2

From: Doc G

----- Original Message -----
From: Richard Bennion
I have an LX200GPS and use T-Point to improve pointing accuracy.

I can get the pointing accuracy to less than 1.5 arcminutes everytime
with a short 10 point mapping run. This is down from about 8-10
arcminutes standard pointing.
----- End of Original Message -----

I want to point out that my work was done some years ago. It was in the late 1990s as I recall. It is true that a very poor scope mount is hard to improve with T-point type programs. But if the scope and mount are mechanically stable, that is, the scope always does the same thing without much hysteresis (backlash) the pointing can be substantially improved.

I have the general feeling that in the past 5 years many scopes have either started life in better condition or they have be tweaked to the point where they are fairly good pointers. I the latter case, the mount can definitely be improved and will give pointing to a (very) few arc minutes. I have had many reports of one or two arc minute pointing accuracy over the whole sky.

It is very important to do the T-point model with the scope loaded exactly as it will be in use. Weight and balance can have a strong effect on the model since the weaker mounts are more flexible. My general feelings about the usefulness of T-point like modeling is that these programs are definitely worth while if you have a reasonable mount in the first place.

----------------------------------

Subject: Is SMT Worth It? --part 3 of 3    Top

From: Bob Denny <rdennya_tdc3.com>

One other thing to look at, if you have a CCD camera, is ACP3. It has a "self-learning" pointing corrector, and it also re-centers as needed so that your images are centered starting with the very first one. As you acquire more images, it learns from the centering errors and teaches the pointing corrector on the fly. <http://acp4.dc3.com/index2.html>

rule

.

Subject: Optical-Mechanical Alignment for GPS Model    Top

From: Bill Drelling <gatorchasera_tearthlink.net> Date: Aug 2002

I actually started to use the Mark Simpson's OTA Alignment Method. It is great. But it is written for the LX200 Classic. I have the GPS version. The difference is that with the GPS version, you cannot turn the optical tube over on itself the way the classic allows. The GPS tube rotates from just past the vertical in the up direction to just past the vertical in the down direction ... maybe for a total angular motion of about 200 degrees at most. In other words, it rotates the direction it points from straight down the fork arms pointing to the base, to straight up the fork arms pointing towards the sky with only slight motion past the vertical.

That is why I had to resorted to a fixed land object to start correcting the optical-mechanical misalignment. I had all day to tweak it with plenty of light to play in. I later took it out at night and tried to get the fine alignment finished with Polaris, but it was too difficult due to the various factors that affect rotation of the tube and adjustments:

  1. declination error,
  2. optical-mechanical tube misalignment error,
  3. "slop" in the wedge, and
  4. my own impatience

Declination error and optical-mechanical tube misalignment are closely tied together because it is hard to see which is which through the eyepiece. The best I could do was get the stars to rotate in an oval pattern within the confines of the reticle--which means I am close. Problem was figuring out whether the optical-mechanical tube misalignment was reflected in the length or width of the oval pattern of star rotation.

To complicate matters, there is always a little slop in the wedge. This is seen when you adjust the machine screws. Only a little pressure is required to turn the screws and move the optical tube, but that is all it takes to make a slight motion of the wedge (I use the Super Wedge on my 8" LX200GPS). All these factors combine to make the fine adjustment complicated.

What is need, ideally, is a way to make the adjustment with the scope in the Alt-Az mode. This is why your procedure works so well with the Classic LX200. Since the GPS tube cannot rotate over on itself, however, your procedure doesn't work with it. Unfortunate.

rule

Subject: Meade Dew Shield on GPS?     Top

From: "messier27" <messier27earthlink.net> Date: Sep 2002

The current Meade Hard Dew Shield does not fit the LX200GPS units. The LX200 Classics had a groove running around the casting at the corrector end of the scope; the set screws for the dew shield locked into that groove. The LX200GPS unit does not have this groove?

rule

Subject: GPS Mirror Lock Like Classic? --part 1 of 2  Top

From: Bill Dougherty <bd5572a_tyahoo.com> Date: Mar 2004

Walt Cooney wrote:
>Can anyone direct to some information on the GPS model mirror lock mechanism?
>Did they just install the equivalent of a shipping bolt that can be latched
>and unlatched or is it something more like the Bisque mirror lock collar?

No, the GPS mirror lock works very differently. It is a collet type mechanism that immobilizes the center mount of the primary mirror where it slides along the central baffle tube. I have a 10" GPS and its mirror lock works extremely well --- very secure but producing no stress on the mirror itself. I consider it to be the single most significant improvement of the GPS over the Classic.

I don't have a picture of the mechanism. It is hidden beneath the back end plate of the OTA. The locking knob has a gear on the inside end of its shaft. It engages teeth on the outside edge of a large metal disk connected to the mechanism that locks the position of the mirror on the central baffle tube. Rotating the locking knob one direction rotates the large disk to tighten the collet on the central baffle. Reversing direction loosens it.

The teeth do not extend all the way around the large disk. So sometimes the locking knob gear jams to a stop before the lock is fully engaged. Soon after the GPS scopes first started shipping Buck Harley discovered that in such cases you can remove the locking knob with its shaft and gear, then reach in and rotate the large disk with your finger. Replacing the locking knob will now allow sufficient rotation to fully engage the lock. If you happen to move the large disk in the wrong direction, then just repeat the process and move the disk in the other direction.

You don't need to tighten the lock down hard. Just a little snug is enough. You should not attempt to use the coarse focus knob while the mirror is locked. Damage to the focusing mechanism could result.

This design is intended to precisely hold the mirror position. So, yes, it is meant to allow effective use of a separate guide scope by eliminating mirror flop when in the locked position.

Are you saying that the central baffle tube itself is moving inside the OTA as the scope slews across the sky? The mirror lock could not do anything about that, since it secures the position of the mirror mount onto the baffle tube.

Of course, if the mirror lock is disengaged to allow use of the coarse focus knob, then the mirror is free to flop around as much as ever. Resetting the lock will tend to move the mirror back to roughly the same angle has it had in the previous locked state, but this position can vary somewhat with each use of the lock. For instance, if you want to test GOTO accuracy, then you need to set the lock before the first alignment star and not touch it again until after the last test star is recorded.

Using the coarse focus knob while the mirror lock is engaged will result in severe image shift, and could damage the coarse focus mechanism. So changing the focus with the mirror lock engaged requires use of a secondary focuser, such as the MicroFocuser included with the GPS scopes.

---------------------------------------------------

Subject: GPS Mirror Lock Like Classic? --part 2 of 2  Top

From: Roger Hamlett <ttelmaha_tntlworld.com>

There is a measurable bend in the baffle tube. The 'key' problem to remember, is that any component before the secondary, has it's effect on the light path amplified by a factor of about 5*. I calculated that for an LX200/12, the tube itself would bend by about 0.3 arc seconds through 180 degrees, with the weight of the mirror, when at the normal focal point (I measured where my mirror was, for the scope focussed about 4.5" behind the rear of the focuser). This then gives an 'unavoidable' error from this source alone, of about 1.5 arc seconds. The rear plate (I was guessing on the aluminium alloy used, but assumed 6061 - similarly I was guessing on the plastic used for the baffle tube), gave a slightly lower distortion, but brought the total up to just over 2 arc seconds. There was also a _tiny_ bend in the mirror itself. In a sense, there is a 'minimum' movement, that is as far as I can see, unavoidable for this design, no matter how well everything else is locked. I'd put this at perhaps 2 to 3 arc seconds total for the worst case (180 degree) movement of the scope.

Moving the coarse focuser with the lock engaged, first 'rocks' the assembly hard to one side or the other, and then tries to 'scrape' the collet along the baffle tube, putting much more force onto the focuser itself, and all the other components, than they are really designed to take. With the 'lock' done up, and moving the scope round the sky, the total movement, in the axis parallel to the line through the coarse focus knob, and the centre of the tube, was down close to the 'bending' limits. However at 90 degrees to this, there was still a significant shift. It makes sense if you think of the system as being locked at the collet, and at the focuser shaft, it can still rock at the front at 90 degrees to this line, till the end of the outer tube touches the inner tube.

The clamping force of the collet, reduces this motion, but does not completely remove it... I must admit I did find myself wondering about careful placement and design of the guidescope mounts, to at least partially compensate for the motion, and wondered if this was how some systems appear to have very good responses. When dealing with 'pure bending' (as opposed to nasty shifts/rocking motion), it would be possible to site the guidescope, so that it's bending is in the same order as that of the main scope, and get a final result that is better than one scope on it's own. As has been mentioned by another poster, Al Testani, was doing a lot of work in this area, trying to measure and model the errors between guidescope and main scope across the sky. It might well be worth talking directly to him, to see how he was getting on.

rule

Subject: LX200GPS Adjust Guide Rate Feature?  Top

From: Dick autostaretx <autostaretxa_tmindspring.com> Date: Mar 2005

> Does the GPS have the 'adjust guide rate' feature?

Yes. On the keypad it's under: Setup > Telescope > Guide Rate

and has a range of zero to 100% of sidereal. The "factory default" is 66%

I provide free patch kits for the firmware (posted to the LX200GPS Yahoo Group's Files area), and one of their features is extending that range to 200% of sidereal.

rule

Subject: How to Calibrate Motor on LX200GPS ?  Top

From: Rich Swanson, Date: Feb 2005

From the LX200GPS group files section: <http://groups.yahoo.com/group/lx200gps/>

I attempted to train my 10" as soon as I got it. Turns out that it worked great. And the best part is that I didn't even have to take it outside to do it.

  1. Get a laser pointer.

  2. Find a way to keep the laser pointer on by itself. I just wrapped a piece of tape around the trigger button.

  3. Tape the laser to the OTA in some manner that the laser point projects onto a wall.

  4. Tape a piece of paper, which you have drawn a target on, on the wall to act as your targeting object.

  5. Complete the training process as described in the manual or on the AS II handbox screen. You don't even have to look in any eyepieces. Just guide the laser point back to the target. VOILA!!! Laser Trained Telescope!

Editor's note: here's another method for training the GPS drives in polar mode. Outside link.

rule

Subject: Parking the GPS Scope  Top

From: Barry Gerdes <barrygastroa_thotmail.com> Date: Apr 2005

The Park and sleep feature is not well explained in the manual and does cause some confusion. I have written a version that I worked out for my understanding that may be of some help. You will find it on my web site (see below) under "Sleep and Park" on the LX200 files page:

<http://www.geocities.com/barrykgerdes> or direct download of .doc file: <http://www.geocities.com/barrykgerdes/Slp_park.doc>

rule

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