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Space Forum / Astronomy / September 2004LX200 RA tracking problems (are they the same for 14" LX200's)
I've begun CCD imaging with a pier mounted 10" F/10 LX200 Classic. After the anticipated (usual) problem elimination phase, one fundamental issue remains. The RA tracking (error graph) shows random spikes of +/- 1-4 arcsec at frequencies of 1 second or less. This "noise" is random and happens throughout the 8 minute worm cycle, not intermittently. I can successfully train out periodic error (manually or with CCD), but after training, auto-guiding is worse due to the random spikes. Even with fast exposures (0.1 sec) the guider sees the error, but by the time correction is applied, the RA error has changed so overcorrection often results. PEC adjustment compounds it (if PEC is on). So far, my best images were made by stacking 1 minute unguided frames with PEC training erased! But RA spikes still manifest (too often) as elongated or doubled stars. Sigh! Since I really have exhausted all other possibilities, it MUST be the RA drive/gears of the LX200. It can't be seeing as it doesn't happen in the Y direction. I've tried loading to east and west, and perfect balance. I've measured error with guiding active and off (spikes in both cases). I have perfect polar alignment and I tried all variations of aggressiveness and calibration settings. It looks like I've got to disassemble and clean the RA mechanism as it is the only viable cause remaining (and this worked for others from what I've read). I'd hoped to avoid this altogether and I'm minded to make do as I intend(ed) to buy a 14" LX200 at the end of this year (observatory and mount were sized for a 14" SCT not the 10" SCT I currently own. How's that for aperture fever "built in" :-) So my question is does the 14" LX200 have exactly the same RA/guiding issues as the earlier (8", 10" and 12") models or is the quality better these days? I'm not so sure that I want to spend £5,500 for a bigger scope if it's likely to have exactly the same (guiding) limitations even if it does have twice the light grasp. Or perhaps I've just got the wrong impression from using a second-hand (old?) Classic LX200. Cheers Beats PS. I don't want a GEM and I DO want more aperture and resolution. > So my question is - does the 14" LX200 have exactly the same > RA/guiding issues as the earlier (8", 10" and 12") models - or is the [quoted text clipped - 3 lines] > I've just got the wrong impression from using a second-hand (old?) > Classic LX200. I'ma member of a local astronomical society. quite a few of our members have LX200s both classic and GPS. None of them has spoken of the error you are having. It sounds as if you have grit in between the worm an wheel... In your situation I would open up the LX200 and clean the worm and wheel as well as possible, before re-greasing and reassembling... From what I have seen of my friends' 'scopes, the LX200GPS does track much better than the LX200Classic... Rarius > From what I have seen of my friends' 'scopes, the LX200GPS does track much > better than the LX200Classic... Thanks Rarius, exactly the kind of anecdotal observation I was looking for (and all the better because it's a positive one :-) There's surprisingly little comparitive info around for the 14", so keep 'em coming folks. I'll summarise if enough "sample points" turn up. Thanks. Cheers Beats > I've begun CCD imaging with a pier mounted 10" F/10 LX200 Classic. > [quoted text clipped - 37 lines] > > PS. I don't want a GEM and I DO want more aperture and resolution. This sounds like dust. If you think about it, the error you are talking about, is in the same order as the size of pollen grains/particles of smoke etc.. If the gear is about 6" in radius, then the jump corresponds to about 30 micron particle sizes, when smoke particles are normally quoted as around 40 micron. You need to scrupulously clean the main gear, and worm, and relubricate with a really good lubricant. This is probably just 'muck' that has got stuck in the grease with time. It is actually a lot smaller in size than the sort of jump that is often seen from LX200's when new (where metal shavings have got left in the mechanism...). The metal surfaces usually improve with use, developing a polish that is not there on the new scopes. Hence your thoughts to clean the mechanism are the way to go. Best Wishes > I've begun CCD imaging with a pier mounted 10" F/10 LX200 Classic. > [quoted text clipped - 10 lines] > frames with PEC training erased! But RA spikes still manifest (too > often) as elongated or doubled stars. Sigh! I'm not familiar with the gears on the LX200, but if it has a series of spur gears somewhere they may be too tight and "cogging". A few LXD55 owners had this problem due to over tight gear mesh. -tom If you plan on keeping the scope for a long time...just spend the $ if needed and get a set of custom gears made if you want it next to perfect. Our club has a 16" LX200 and the RA drift is all over the place...back and forth..within 5 minutes of guiding. It has been sent to Meade twice and each time they say its within spec. I don't see how anybody or anything can photograph @ 4000mm. I took a 15 min exposure through a piggybacked scope and guided through the 16" with a 9mm crosshair eyepiece...I couldn't hardly look away for a second or two before quickly having to look back to see the star running out of the cross hair..toward the first bullseye ring...either one way or the other...say half the diameter of the Trapezium...if you draw a circle through the 4 stars. I'm using this as a guide because this is what I was guiding on at the time. I didn't have the PEC on ...just guiding in regular mode or whatever. Maybe play around with the drive system of the 10" first and see what works and what doesn't as far as adjustments and grease and what not before buying the 14". You could become the SCT motordrive GURU!!!! Good Luck! Joe > Our club has a 16" LX200 and the RA drift is all over the place... > I didn't have the PEC on ...just guiding in regular mode or whatever. That would account for the major wobbles you were getting then. PEC must be on! My scope has a couple of points that behave as you describe if PEC is off. Training the drive removes this altogether (I'm just left with the random noise though). Actually, it's better for you 16" folks as I read somewhere that PEC training is set at the factory. Bloody luxury :-) Cheers Beats Lucky??? It has screwed up twice and We had to ship it back at our cost...plus being without a scope for a month or so. Joe > Lucky??? It has screwed up twice and We had to ship it back at our > cost...plus being without a scope for a month or so. "Lucky" he snorts - slamming down his coffee in righteous indignation! Tee hee. Sorry! Your response conjured up that mental image. Raised a bit of a chuckle here :-) Does sound like you've had a bit of a runaround. I know what you mean about being without the scope though. That's why I'm not keen to get into serious disassembly of mine, just in case I break something terminally and then have to wait for someone else (e.g. Meade) to fix it for me. I'd have thought that you could expect much better service and performance at the price point of a 16" though. Weren't they about £27K not that long ago? They seem to have dropped in price dramatically lately (though still a big leap in cost from 14" to 16"). Are they the same scope at the new price point (if I'm not imagining the new price point). When did your club get theirs? Cheers Beats Got it in 1999 for around $16K new. Joe > I've begun CCD imaging with a pier mounted 10" F/10 LX200 Classic. > [quoted text clipped - 7 lines] > error, but by the time correction is applied, the RA error has changed > [...] Just musing: are your dew heater(s) running off the same power supply? If so, don't do that. > Just musing: are your dew heater(s) running off the same power supply? > If so, don't do that. CCD, dew heater, scope, filter wheel and PC each have separate power supplies (bricks and attendant spaghetti) which are all plugged into a single surge-protected mains strip. This is just a simple 6-way jobby with an on/off switch and an over-bright green light (now covered in insulation tape :-) I don't think power is the issue - but it was a variable I hadn't considered. Cheers Beats |
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