Well OK Tom sent me an off-list note so you guys have persuaded me to give this
a whirl. On a c8 I suppose I'm looking for what, maybe a 2 inch or 2.5 inch
hose clamp at an auto parts store?

I'm deep into about 25 Pentax XW units of home repair and remodeling so I don't
know when I'm going to get to this project, but will keep everyone apprised.

thanks
Greg N


--- In sct-user@yahoogroups.com, John Mahony <jmmahony@...> wrote:
>
>
> ----- Original Message ----
>
> > From: gnowellsct <tim71pos@...>
> >
> > Thank you John for your comments.
> >
> > I guess I don't understand why an irregularity or tilt in the hose clamp
would
> > not affect the total travel of my laser beam. Basically my mirror is on a
> > "plate." It is possibly tilted. As I rotate it around, the tilt will cause
a
> > fixed ray to wobble back and forth to different positions. Zero tilt leads
to
> > zero wobble. This much, I get.
> >
> > But it seems to me that the "predicate" of this measurement is a nice even
> > surface on the back for the whole thing to rotate on. I'm not sure I could
> > improvise something that would be better than the rear casting as a support
for
> > this test.
>
> The baffle tube provides the "even surface" to rotate around. The hose clamp
is used to keep the mirror cell forward enough so parts on the back of it don't
hit anything inside the rear tube cell as you rotate the mirror.
>
> If the rear of the mirror cell has irregularities so that the mirror moves
forward/back along the baffle as you rotate it (because these irregularities are
hitting the hose clamp), that will have little effect, since that only makes the
mirror move forward/back on the baffle. In fact it will have no effect if the
laser is aimed parallel to the baffle tube axis.
>
> -John
>
>
> >
> > --- In sct-user@yahoogroups.com, John Mahony wrote:
> > >
> > >
> > > ----- Original Message ----
> > >
> > > > From: gnowellsct
> > > >
> > > > I got this c8 because the price was right: I wanted the SP mount it came
> > on.
> > > > The c8 came with it. So I keep it specifically for these kinds of
projects,
> > as
> > > > a training instrument. So I will see what kind of spin I can get from
it
> > but
> > > > will probably recruit one of my club friends as people get a perverse
> > > > fascination from disassembled SCTs.
> > > >
> > > > Three questions.
> > > >
> > > > 1. You mentioned you moved the mirror forward from the rear casting to
do
> > the
> > > > spin. How do did you support it?
> > >
> > > He mentioned a hose clamp around the baffle tube below the mirror.
> > >
> > > > 2. I don't have a clear idea as to how one mounts the laser to get a
> > meaningful
> > > > measure: the angle from which the light should fall. Seems to me one
wants
> > the
> > > > laser "firing straight down" but it has to be rigidly held so as not to
bias
> > the
> > > > mirror measurement. You seem to have chosen about 75% out from center
for
> > the
> > > > laser spot. Any particular reason?
> > >
> > > Details here don't matter. If a sphere is tilted, all parts tilt by the
same
> > angle. A laser reflected from any angle, off any point of that sphere, will
> > "wobble" by twice that angle. So the only important part is to make sure
the
> > reflected ray is long enough to see the variation.
> > >
> > > > 3. You use a level or something to make sure the mirror is pointing
straight
> >
> > > > up?
> > >
> > > It doesn't have to be straight up. In fact I think it would be best to
have
> > it tilted some, so that "mirror flop" (in the traditional sense), which
would be
> > worst when straight up, doesn't interfere.
> > >
> > > -John
> > >
> > >
> > > > Perhaps putting the ota on a mount would be the easiest way to have
> > > > adjustment parameters.
> > > >
> > > > thanks Greg N
> > > >
> > > >
> > > >
> > > > --- In sct-user@yahoogroups.com, "tom_krajci" wrote:
> > > > >
> > > > > --- In sct-user@yahoogroups.com, "gnowellsct" wrote:
> > > > > >
> > > > > > ...this is an exercise I could actually do, I could put a picture
> > > > > > up of the wobble. Sounds to me like a two person job what with the
> > > > > > laser and tracing the wobble parameter and someone to spin the
> > > > > > thing down on the floor....
> > > > >
> > > > > A movie would be sexy, visually striking, but I just put a piece of
> > > > > masking tape on the ceiling...rotated the mirror...and marked the
> > > > > extremes of the dot's travel. That is a one-person job.
> > > > >
> > > > > See:
> > > > >
> > > > >
> > > > > specifically
> > > > >
> > > > > IMG_2591a.JPG
> > > > >
> > > > > Then we can do some trig. to determine your mirror misalignment...we
> > > > > only need projection/reflection distance, and max spot wobble across
> > > > > the screen at the projection distance.
> > > > >
> > > > > --
> > > > > -------------------------------------------
> > > > > Tom Krajci
> > > > > Cloudcroft, New Mexico
> > > > > http://picasaweb.google.com/tom.krajci
> > > > >
> > > > > Center for Backyard Astrophysics (CBA)
> > > > > http://cbastro.org/ CBA New Mexico
> > > > >
> > > > > American Association of Variable Star
> > > > > Observers (AAVSO): KTC http://www.aavso.org/
> > > > > -------------------------------------------
> > > > >
> > > >
> > > >
> > > >
> > > >
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> >
> >
> >
> >
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