Jim...

Can send you some pictures your my dial indicator mountings, Also, I can
write step-by-step instructions if you don't have a
clear picture of what we're doing.
Think you
PS Have not got into ccd but would like to start with 35mm camera to get my
feel wet. never done this before. First timer

----- Original Message -----
Sent: Saturday, May 05, 2001 10:16 PM
Subject: [M]: Re: Aligning with dial indicators and CCD


> I agree with Mike on the usefulness of dial indicators for drift
alignment.
> I'd like to add so notes of my own.
>
> > I used my CB245 CCD for this- any ccd camera will work
> > fine.
>
> I use the ST7 and the DOS version of CCDOPS.
>
> >My indicators .. each(~20.00USD) for base and indicator. I wouldn't
> advocate purchasing a pair
> > just for this ...
>
> I disagree - for $15 - $20 x 2 for the pair, the dial indicators are worth
> it. If effect, they make any wedge precisely adjustable. ( I use the
Meade
> Superwedge.)
>
> >If yours in nonferrous you may be in for a
> > challenge mounting the indicators.
>
> I still have a wooden pier (gotta replace it with steel some day), but
just
> screw a steel plate where the magnetic base needs to sit.
>
> > I found my MSW moved several hundreths of an inch in
> > Azimuth while adjusting elevation!!
>
> I wonder what's going on there? Mine doesn't do that.
>
> >I highly recommend the Milburn wedge.
>
> A friend has a Milburn and it is indeed very good; if I were buying a new
> wedge I'd get that one. However, with the dial indicators, the MSW can be
> made adjust well. I can't speak for any difference in stability between
the
> two.
>
> > Make adjustments and follow the normal provisions for
> > drift aligning but the ccd replaces the reticle ep.
> > Keep track of adjustment and movement. Write the
> > indicator locations down to give yourself an idea how
> > the wedge is moving. If you have to reverse direction
> > you will be able to see how much backlash you have to
> > overcome to change direction.
>
> Yes, with the dials, backlash is a non-problem. You move the wedge to
reach
> a position indicated on the dials - you don't have to worry about
mechanical
> slop or wondering how much movement occured when a crank on the knobs
caused
> a larger than expected lurch of the wedge. You know exactly what's
> happening to movements. If you overshoot, it's easy to go back to the
> position you were aiming for.
>
> > To measure drift- align the ccd so that NSEW are
> > aligned appropriately.
>
> ST-7/8 users have to use this alignment anyway to get good guiding.
>
> >I use an eraseable marker and a rule to scribe reference
> > lines on the monitor.
>
> If you isolate one bright star in the field of view, CCDOPS will give its
> position in x, y coordinates; all software I've seen will let you measure
x,
> y position of stars. If you align the x, y axes of the camera with RA and
> DEC of the telescope as Mike described, the difference of the bright
star's
> y position over a period of time (I use something like 10 minutes after I
> get close) gives drift in pixels/minute. I note this drift measurement
and
> the position in RA or DEC (depending on which one I'm working at the
time).
>
> Some cautions here. Be careful in figuring out the direction of star
drift.
> The 0, 0 position in the CCDOPS image is the upper left corner, so if the
> star drifts from y = 100 to Y = 110 after a period of time, the star is
> dropping in the image, not rising as the increas in y value might imply.
> Also, the orientation of your camera on your telescope may cause North to
be
> up (or left or right) on the image, not down. Work out what the drift
> direction means carefully.
>
> >I often achieve a total drift between 25 and 35
> > arcseconds/hour or better.
>
> I'll have to convert my measurements to arcsec/hour to see how I compare.
I
> try for no more than one, 9 micron pixel/10 min drift - I often get no
> measurable drift in 20 minutes.
>
> > Again this may be a bit tedious but I found it a good
> > exercise for a bright moonlit night.
>
> This can indeed be tedious, but you can converge directly to a fine
> alignment. It's really worth the effort.
>
> Ettore, I can send you some pictures of my dial indicator mountings, if
> you'd like. Also, I can write step-by-step instructions if you don't have
a
> clear picture of what we're doing.
>
> Jim Seargeant
>
>
>

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