Weasner's 8" LX90-ACF Report #11

11 October 2008

8" LX90-ACF - Final Results

This report is a follow-up to my previous report and will be my last report on the 8" LX90-ACF. You'll discover why when you reach the end of this report.

The weather cleared up Sunday, 5 October, so I spent a couple of hours with the new LX90 outside. I did have to CALIBRATE SENSORS as the alignment stars were way off. Once I did that, alignment stars were well within the 8x50 finderscope field-of-view. During this limited use I did not have any significant vibrations. Occasionally there would be a very small image jerk (in azimuth) but for visual work it was not distracting. It would be interesting to see what affect polar mounting (on a wedge, which I don't have) would have for photography and whether that small jerk would be a problem.

But so far, after this initial testing, things looked good.

One thing I did notice during set up is that without any of the accessories attached, the tube is front heavy. With all the standard accessories (LNT, 8x50 finderscope, 1.25" diagonal, 26mm eyepiece) attached, it is rear heavy. Using a 2" diagonal and eyepiece it is even more rear heavy. I also noticed that the LX90 manual has been updated and now reflects the LNT, GPS, and ACF optics. The manual that came with my previous two LX90-ACF telescopes back in April 2008 had an older manual.

On Wednesday, 8 October 2008, I went to Oracle Observatory to do more extensive testing. And here are the results:

About an hour before sunset, I set up the LX90. I powered the LX90 from a Celestron 7AH Power Tank using the Meade DC cable. I did a RESET, CALIBRATE MOTOR, and TRAIN DRIVES (both axes) using an object on a distant mountain. I then did an Auto Align and accepted the alignment stars as centered (since it was still daylight). I then did a GOTO the moon, which was placed just outside the 8x50 finderscope field-of-view. Over the next couple of hours, I viewed the moon and Jupiter (which was low in the southwest), and both remained steady with no vibrations. Both objects were very clear and crisp in all the eyepieces I used.

During this period of time I tested some accessories, which I'll report on separately.

After dark I did a CALIBRATE SENSORS (to correct the initial pointing error). I then did the Auto Align while using a Meade 9.7mm eyepiece with a Meade 2X Barlow Lens (yielding a magnification of 412X) to precisely center the alignment stars. From that point on, all GOTOs put the object in the 9.7mm eyepiece + 2X Barlow Lens FOV. Very impressive GOTO accuracy.

I now began my tests to check for any image vibrations like I had seen in my previous two LX90-ACF telescopes. I initially looked at Jupiter, M13, and M57. All were steady with no vibrations.

I then went to Vega, and almost immediately Vega began to jump around somewhat in the eyepiece. This jumping was not due to wind (which was calm), road or other external vibrations, or atmospheric turbulence. It was similar to what you would see if you tapped on the side of the OTA. Except that it would not dampen out like a tap-induced vibration. It would start and stop at varying intervals, but all within a few seconds to a few minutes. It would last for several seconds when it was jumping. Vega was at an altitude of 65 degrees (on the fork arm scale, which I did not calibrate). I removed the Barlow Lens and viewed Vega with just the 9.7mm eyepiece (206X), still jumping around noticeably.

I then moved to Mizar (alt 19 deg), no movement. Very steady in the 9.7mm eyepiece.

Then to Altair (alt 61 deg), no movement.

Then Fomalhaut (alt 18 deg), no movement.

Deneb (alt 80 deg), no movement.

So I went back to Vega (now at alt 63 deg). It jumped around.

Went to Polaris (alt 36 deg), no movement.

Capella (alt 6 deg), no movement.

Double Cluster (alt 35 deg), no movement.

Shedir (alt 49 deg), no movement.

Markab (alt 59 deg). It jumped around. So it wasn't just Vega that would jump.

M13 (alt 36 deg), no movement.

Back to Vega (now at alt 58 deg). It continued to jump around. I decided to let the LX90 stay on Vega for awhile to see if the jumping diminished as it got lower in the sky. I switched the eyepiece to the Meade 12mm illuminated reticle eyepiece. Vega's (now at alt 55 deg) movement was generally covered a distance in the eyepiece that the reticle parallel lines are separated. That's a lot of movement as you can see from this graphic from the eyepiece ad:


At this point I decided to switch to using the internal battery power. I did another CALIBRATE MOTOR and another Auto Align.

Back to Vega (now at alt 51 deg). It still jumped around.

Vega (now at alt 49 deg). Still jumping.

At this point I decided to do some more accessories testing. After I completed those tests I went back to Vega (now at alt 39 deg). It was still jumping around.

I then went to Deneb (alt 62 deg). It jumped now. It hadn't jumped when it was at altitude 80 deg.

This ended my tests on the vibration problem. I tested at several vertical elevations and horizontal azimuth positions on both sides of the meridian. Three objects (Vega, Deneb, and Markab) on both sides of the meridian experienced the problem. But other objects at similar elevations and azimuth positions were rock steady. As I saw with the first two LX90-ACF telescopes, the vibrations occur in some orientations and not others. However, the vibrations are certainly reduced in both amount and orientations where it occurs in this new LX90-ACF with AutoStar 4.4Ea. But Meade still has some more work to do. I remain confident that they will get the problem cured.

It is worth noting that not all users may experience the same problem I have. Certainly some users have experienced it but apparently not all new users are seeing this problem. Optically, the LX90-ACF is one amazing instrument. The improved optics in the ACF model is truly a nice new feature.

I contacted Meade and OPT to see how we'll proceed from here. Meade wants to do some very specific testing on this particular 8" LX90-ACF and that could take some time. Rather than keep me waiting any longer since it has been almost 10 months since my 8" telescope was stolen, they offered to exchange the 8" LX90-ACF with an 8" LX200-ACF. I told them I would be honored to be counted as a Meade LX200 user and accepted their offer. I should have it within a few days.

As a result of the telescope exchange I'll be starting a new 8" LX200-ACF reports page once I get the new telescope. I'll link to it from the "LX90-ACF Table of Contents" page as well as my ETX Site Home Page and main Home Page.

Go to the LX90-ACF Table of Contents.

Go to Mike & Laurraine's Home Page.

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