Weasner's 8" LX90-ACF Report #2

11 April 2008

After waiting a few nights for the winds and clouds to go away, the LX90 was finally able to get "first light" on 10 April 2008.

But before I report on that here's an update to my Unpacking report. Henrik van Holthoon noted my comment about the problem reaching the Zenith with the AutoStar set in its handle. He didn't think the problem should occur with the handle on the left side and he was correct! I guess I hadn't reversed the clamp when I switched sides. With the clamp reversed there is no interference. However, the AutoStar handle interferes somewhat with gripping the fork arm handle for moving the mount but that probably won't be a major problem. Thanks Henrik!

One handle I do miss is the one that was at the rear of the OTA on my LXD75-8"SC. That was handy for moving the OTA by hand.

Henrik also warned me about the cord wrap since the control panel is mounted on a fork arm (unlike on the ETX-90, -105, and -125 models). As the telescope slews horizontally the cords go with it. For the AutoStar this means if you have it stuck on a tripod leg (using Velcro) then it could be pulled loose from the leg or it could even prevent the mount from slewing. If you have an external power source connected you have to be certain there is sufficient cord length to avoid a problem. Alternatively, you can enable "CORD WRAP" on the AutoStar to prevent the LX90 from doing too much rotation before it reverses direction during GOTOs. Thanks again Henrik!

Now on to the first light report.

I had previously done a CALIBRATE MOTOR and TRAIN DRIVES, and aligned the LNT/Smartfinder and 8x50 finderscope so all was ready for tonight. After the LNT and GPS did their thing the first alignment star, Sirius, was just outside the finderscope field-of-view (FOV). The second alignment star, Arcturus, was halfway from the center to the edge of the finderscope. After completing the alignment, I did a GOTO Saturn and it was placed in the 26mm eyepiece (77X) FOV. In fact, all GOTOs were excellent and put the selected object in the 9.7mm eyepiece (206X) FOV. I did some star tests and decided that the collimation was good. I also looked for but could not detect any coma at the field edge, no matter the eyepiece focal length (out to a 1.25" 40mm eyepiece; I will try 2" eyepieces at a future date).

Saturn, Mars, M42, the Pleiades, some stars, and the near First Quarter Moon were observed. I used 40mm (50X), 26mm, and 9.7mm eyepieces, with and without a 2X Barlow Lens, and all views were very nice. Well, very nice when they were stable.

While tracking an object, every 3-5 seconds there would be a rapid "thumping" sound which created a nasty vibration. At 206X, Capella would swirl around for 1-2 seconds in an oval pattern as large as Saturn's rings! It seemed to happen regardless of the telescope's orientation. It definitely made for lousy viewing and would make astrophotography impossible. While slewing from object to object there was no thumping sound or vibration.

I redid the CALIBRATE MOTOR and TRAIN DRIVES but the sound and vibration did not go away. I gave up on doing any more during the night.

Today I powered on the LX90 and set Targets to Astronomical. Within a few seconds the thumping sound started up and repeated every 3-5 seconds. It sounds somewhat like someone making a "raspberries" sound. It lasts about 1-2 seconds, pauses for 3-5 seconds, and then repeats. The length of the sound and the pauses between the sounds varies. During the sound you can feel a very definite vibration in the mount and it is that vibration that ruins the view through the eyepiece. There definitely seems to be a mechanical problem. I contacted OPT (the dealer where I purchased the LX90) and they will contact Meade and let me know how they want to proceed.

Stay tuned...

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Copyright ©2008 Michael L. Weasner / mweasner@mac.com
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