Your intellectual honesty is appreciated and refreshing. I consider your
experiment to be successful in helping us to learn.
Thanks!
Pat Riley

-----Original Message-----
Sent: Saturday, June 23, 2001 10:42 AM
Subject: [M]: retraction of vibration control by bungee method


This is moderately embarrassing, but regardless I need to correct the
record - or at least amend it substantially with some disappointing
results.

Not too long ago I triumphantly posted a method for reducing
vibration in a permanently-mounted 16" lx200 by hanging weights
on bungees of the right elasticity from the end of the OTA. That
method appeared to be similar to the use of finger-pressure on
the eyepiece, which accomplished the same goal.

I've now spent four times as much time trying to get the method
to work as well as it seemed to when I first tried it. The bottom
line is that, sadly, I think the method may not work at all.

I would print an unprovisional retraction, but there could be a
reason that it worked so well the first time that I can't
understand and so can't replicate. On the other hand, a string of
coincidences could have accounted for the original results,
which means they had nothing to do with weights and bungees.
There might have been an unusual vibration in the building that
supports the 16" that responded to the weights and misled me
the first time I tried this, but even if so, unusual would mean
not generally useful.

I also spent a good chunk of time devising lead weights on
springs of various kinds in an attempt to reduce the higher
frequency vibrations (about 10 Hz, as Doc G. reported) of
my 8" wedge-mounted lx200. Nothing worked, despite
tuning the weights to the same frequency as the mount
using an oscilloscope as a frequency meter.

So the use of weights that have a vibration frequency similar to the
telescope don't reduce telescopic vibration, as far as I can tell.
Consequently, I ask Ed Stewart to delete my photo of the bungees
on his web site and I apologize for inconveniences that might have
arisen as a result of my original report.

Rob Preston
Pittsburgh PA

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