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Subject: Re: Improving the LX-200 (MW)
From: DK0179@AppleLink.Apple.COM
Reply To: mapug@shore.net
Date: Fri May 05 02:55:00 1995

Gary put a list of improvement suggestions to the LX 200 board. Some weeks ago I send the letter below to Meade, the answer is until now not clear, it seems they may consider these changes, but put them into action is another thing... It looks as if the only way to get Meade in talk is if we could find a general consensus - read pressure - on this board. The list included is long, sorry, but I tried to write it as kind as possible... Some of those problems belong to the 16 " in particular, other are part of the AstroSearch , and LX200 interface in general. Best greetings, appreciating this network ! Mogens Winther. Dear Ron Ezra, dear Scott W. Roberts, dear Erik Persson, AstroMekanik ! Below you find some improvement suggestions, concerning the 16 " SCT, as well as the AstroSearch software. ........ I have enclosed a list below. The worst problems right now is the wrong tracking rate, and the focus-shift. These problems, and the closed PEC, together with the missing RAlearn are most frustrating. .................... At last, I do include a list of improvement suggestions.Some of these points may look cantankerous to experienced wizards, but they actually do present a problem to my young students. Remembering the co-operative spirit presented by Meade on the LX200 network, I hope you may still find these information's useful . Best greetings, looking forward to hear from you ! Mogens Winther, high school teacher , Astronomy, Math. Phys. Executive member of the ESO founded EAAE , European Association of Astronomy Education, free lance journalist. The tracking problem in particular.. : As the previous measurements published on Internet LX200 discussion board, some 16 " and other telescope owners have real problems about too fast tracking. Below, you may find CCD measures star positions , while our 16 " was running at the 60.1 default STELLAR TRACK RATE . x,y position of centroid, 4 meter focal length. 161,09 81,45 159,58 81,94 157,05 81,39 154,90 81,23 152,04 81,08 149,61 81,04 150,06 80,70 149,68 80,86 150,64 81,33 147,28 80,49 144,40 80,47 143,22 80,64 138.72 80.77 137.75 80.93 136.79 80.18 134.16 80.68 135.29 80.83 134.73 80.56 133.02 79.75 131.27 80.26 128.55 80.54 127.57 80.33 126.29 79.79 The download time for each image is reduced to around 30 sec. . Star placed at the equator/meridian. At 4 meter focal lengths, the 23 x 27 micron pixels of the ST-6 camera cover 1.2 x 1.4 arc seconds of sky. Please notice, the telescope RUNS TOO FAST in RA. Comparisons at different hour angles show this is not an effect of the worm gear being misplaced / eccentric. Again, the telescope runs at 4 meter, falling numbers corresponds a too high westward telescope speed.. Reducing the speed to 60.0 HZ SOLAR rate : 186,98 76,60 189,18 76,09 191,43 76,77 191,72 76,87 191,06 75,72 188,66 76,15 187,18 75,84 187,05 75,34 188,43 76,37 190,30 75,27 192,00 75,57 190,89 75,78 189,80 75,33 189,28 75,08 188,23 75,39 188,46 75,11 188,66 75,18 189,85 75,20 190,16 75,12 190,82 74,80 188,25 75,06 188,07 74,75 188,36 75,10 Please notice, the shift to solar speed makes our telescope follows the stars, now the error is only on the order 6 ". Photographically wizards may tell you that the 60.1 Hz tracking problems are easily counteracted by means of an ST4 autoguide. This is true, but again, working with students, things have to be simple. I here want to quote a recent article, by Dennis diCicco, Sky & Telescope, April 1995, p. 50, when testing a JMI product : "Fifteen minutes spent readying an autoguider is a minor price to pay for a 1-hour exposure, but it's a lot overhead for a 3 MINUTE CCD image. EXPOSURES THAT SHORT DON'T NEED GUIDING, IF THE TELESCOPE DRIVE IS FIRST RATE" As the previous 60.1 Hz data shows, the 16 Inch is not fulfilling this criteria at all, exceeding the exposure time beyond 20 seconds implies trailed star images. This is a pity, when doing school astronomy, the simple SBIG CCD "Track and Accumulate" feature is a really powerful tool. But again, as other 16 inch owner have written too on Internet LX200, you loose far too much time and details if say a 5 minute CCD image has to be divided into 20-25 subpictures in order to avoid trailed images. I do not offend Meade due to the existence of these errors, even the best Steinway Piano will have to be adjusted / tuned after moving. What however bothers me is the fact that much of the 16 " software structure remains closed, or as the manual writes , "totally transparent to the user". This is a new politic, which I dislike. As these tests show, laboratory perfection, and real sky observations need not to be the same. In addition, all telescopes may change in time, imperfections will be worn away, periodic errors will change, etc. All car factories will tell you the same story, mechanical parts change, and adjustments performed during the very first hours of operations should not be made permanent. The 16" will - due to its long focal length - be particular sensitive to such natural changes.. Meade may cover some of the trivial "once in a life time" menus in partly hidden submenus, but the conclusion should be : all vital parameters , including the PEC should be accessible to "the most demanding user". List of suggestions in detail : a. The 16 " has a DEClearn function, allowing for drift in the Declination. Allow a similar function, RALearn. If only one such function is possible, allow the user to choose himself between RALearn and DecLearn. b. All telescopes change as times goes by... The 16 " will be particular sensitive to such changes. Allow the user to Periodic Error Correction-train his own telescope, similar to smaller telescopes. c. Measurements by several people show that the laboratory defined tracking rate is too fast. On our 16 " , stars become trailed already after 20-25 seconds. Allow the user to change the permanent start-up frequency. Increase input accuracy beyond the present accuracy of 0.1 Hz. The German Eckard Alt mounting has a permanent user input ten times more accurate, the JMI mototrak described by Dennis diCicco in Sky & Telescope April 1995, p.51 even allows user input with an accuracy as high as 0.002 Hz. d. If Meade Instruments wants to sell this as a "school observatory telescope" some of the features need to be simplified. Entering the telescope mode "park in home position" now requires quite a lot of attention/ 3-4 subcommands. People may do so, but it scares them fooling around in submenus. In addition, a number of tests show that 20-30% of our students and colleagues wrongly enter to other commands, like the "site", or even worse, the "align" command. Here they get locked, and eventually pull the plug, destroying any careful synchronisation/alignment.. Even if they enter the home command correct, they may take the first visible command, "find home" instead of the correct second command , "park". If the telescope is now placed in high hour angle positions, the "find home" command will imply a home search failure. So , it should be possible to park the telescope by means of a student friendly, EASY visible / foolproof menu. e. The focus knob is to coarse, and should be refined, at 4 meter focal length even a slight turn gives - so my opinion - a far too dramatic focus change. f. Focus-stability is a problem on this f=4 meter Schmidt Cassegrain. As Jason has written earlier, the primary mirror is springloaded. While focusing on a zenith star, and moving down to a lower altitude star, the primary mirror may be shifted forward (due to the coarse focus knob backlash/ springload / reduced gravity-component). In student work this type of occasional focus shift is most discouraging. Jason suggested a brilliant solution, mounting a 1/4" x 3 " bolt in the transport bolt hole. Applying this trick simply locks the mirror , and so - quoting Jason, reduces the gravity mirror slip to less than 10 %. However, on a 16 000 $ scope, these tricks should not be necessary. Imagine , students unaware of this lock-feature, trying to focus by violent force from CCD to say ocular observing. Instead, you should implement a type of linear encoder, displaying the accurate, actual position of the primary mirror. This encoder might be placed close to the transport bolt hole, similar to Jason's focus bolt. I know this type of equipment is mass-produced to prices around 80 $, and applied in CNC machines, etc. g. Allow the user to customise the slew speed permanently. Right now, the slew speed is pre-set to full maximum following each upstart. Observatories running heavy load (25 kilo allowed according to 1992 fax by Ron Ezra, still valid ?) may prefer lowering this speed, in order to ensure long telescope lifetime. Concerning Meade AstroSearch software interface to the 16 " LX200. This software is most valuable, when doing astronomy with students. However, a few points should be changed : h. Daylight saving correction works wrong east of Greenwich - negative longitude. i. As the Dec. Jan. discussions on the LX200 network showed, many telescopes have inaccurate time keeping. Someone wrote "my 10 $ TIMEX watch keeps a much higher precision, then my expensive LX200". It would thus be beautiful if you make an external clock feature possible. Most computers have a extremely precise internal clock. If time keeping is a general problem, it should be possible to let the AstroSearch software resyncronise the system clock automatically at each restart. j. object-symbols are far too weak/ missing , e.g. the horsehead nebula shows no symbol at all. k. when the telescope connection is established, it is impossible to scroll around on the sky for more than a few degrees. If the telescope-point indicator moves to the edge of the screen, and you still proceed further, the scrolling will stop, and the program will recenter itself at the telescope point position. l. your software allows a command, called "Save State". This is a smart feature, enabling the user to customise his software. It would be attractive, if the "establish telescope link" command could be saved too. Working with students, it has to be as simple as possible. m. Object comments in AstroSearch are not very informative, e.g. open clusters should show the number of stars, galaxy information's should display visible information's like "dusty edge on" , distance etc... If not possible, at least the quality index should be present. It should be possible to sort / DISPLAY objects according to this quality index. n. CCD owners are limited to a certain size of objects. Working mostly at f6.3 with the ST6, we look for objects around 10 x 10 arcminutes. Students have problems finding objects of this size within the AstroSearch. Instead they start fooling around with objects far too large, or far too small. It would be nice, if Meade AstroSearch could sort / display objects, according to size interval , e.g. (2 - 4) (4 - 6) (6 - 8) arc minutes size. o. The AstroSearch "synchronise telescope" should not be placed to the upper left, right now it is the first radiobutton visible. If you have computerscared people/students fooling around, they will click on this first radiobutton they see, the "Sync. Scope". Such a wrong command will immediately messes up any alignment. First radiobutton to the upper left should be much more often applied "slew to". p. several letters on this network document that some LX200 alignment stars have wrong positions. If not already done, this should be corrected, revised eproms should be offered at reduced prices. Again, satisfied users are the best advertising possible. q. What does the sky really look like ? The cylindrical projection, your software applies , is probably fast, and accurate at the Sky Equator. However , at our position in Scandinavia, we run for northern stars. Your software here makes star-pictures look strange, the Big Bear is really Biiiigggg ! This confuses my students, could you allow another more natural appearance, like e.g. the user-latitude conical projection ? (it is actually equally as fast).