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Re: (meteorobs) Rotating shutter RPM's

In a message dated 96-08-29 16:42:13 EDT, you write:

<< Forgive a dumb question, but doesn't George's RPM number refer to the
number of 
 flashes of the strobe per minute? If so, then it does make sense as
everybody 
 said, that the highest number of flashes per minute which showed a
stationary 
 marked blade would give the actual number of RPMs of the rotating shutter,
and a 
 halved strobe speed (575 in this case) would give a harmonic of the speed.
But 
 this wouldn't imply a harmonic at 2300 would it? Instead it actually shows a

 "half-rotation harmonic", no? Just curious, since I don't even own a strobe.
 
 Lew, full of technical-sounding but basically dumb questions today... :)
  >>
------
Just a reminder of what I found on my rotating shutter test. When I first
shined my strobe on my rotating shutter, I had no idea that Harmonics was a
possibility.  I've never experienced them before although I've had somewhat
limited experienced with stroboscopes.  The two blades are somewhat
identical...at least that was what I strove for...otherwise the shutter would
be off balance and wobble. The blades are painted black.  Not knowing about
harmonics, I could have just as well stumbled initially onto the correct
RPM's as well as a harmonic without anything to distinugish one blade from
the other. Actually, I did stumble onto the correct RPM a few weeks ago when
I announced that apparently the voltage was to blame from a rural location.
It now appears that the RPM's from my rural observing site and my urban home
are very close...within about 200 RPM's  and perhaps closer. But from the
test I made the other nite I did notice a relationship from the RPM  to the
next faster RPM...whether it be a harmonic or the correct one.  The following
RPM's where the blade appeared stationary were:  450, 650, 1150, and 2300.
   If you take 450 +650 you will get 1150.  Again if you add 450+650+1150 you
will get 2250(so it's off by 50 here).  On a hunch I added 450+650+1150+2250
and got 4500.  It just so happens that I was able to make 4 apparent blades
appear stationary at 4400. At the 2250 RPM you may recall I had both blades
appearing Marked.  1150 was the first RPM setting that had only 1 blade
appeared marked coming down from the obvious too fast speed.   Choosing
between 450 and 1150 was based on this and the most likely candidate since
they appeared identical with the strobe light. This probably means nothing to
anyone other than me...but if you use a rotating shutter, definitely be aware
of harmonics.  One happy note here.  I now feel that I have been using a
relatively ideal rotating shutter speed all along and wasn't aware of it. 
George Z.
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