In response to Ettore's request and others...

It is really rather simple. The use of the ccd has
been outlined in other places and simply lets you see
the drift much sooner as well as be able to quantify
it. This should be done after a good "visual" drift
alignment to tweak things in. It is probably
unnecessary but for a permanently mounted scope the
extra effort to get things perfect is worth it. The
dial indicators give you a measure of the movement of
the axes when making an adjustment. With practice you
will soon learn just how much movement is required to
slow the drift.

I used my CB245 CCD for this- any ccd camera will work
fine. My indicators were obtained from Grizzly
industrial very inexpensively each(~20.00USD) for base
and indicator. I wouldn't advocate purchasing a pair
just for this but if you have or can locate a couple I
think the exercise is worthwhile. Since I also like to
turn metal the indicators were already on hand.

I have a custom pier made from boiler plate and carbon
steel pipe. If yours in nonferrous you may be in for a
challenge mounting the indicators. You will need to
fix the indicators using the magnetic bases so that
they will not move and will suppport the indicators
against the appropriate surface to pick up movement in
the axes. I set the indicators in ~50% to give a
positive indication of movement.

I found my MSW moved several hundreths of an inch in
Azimuth while adjusting elevation!! I suspect this is
why I was never able to get the polar alignment down
"perfect" . I would readjust the az by the same amount
as it had earlier shifted when tweaking the elevation
although the elevation axis also moves somewhat it is
not as pronounced. In terms of az slippage when
adjusting elevation on the Milburn I found it much
better ( only a few thousandths). The adjusting
controls are also very smooth. I highly recommend the
Milburn wedge.


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.

To measure drift- align the ccd so that NSEW are
aligned appropriately. I like to see the NS drift move
up and down but left to right will be all right just
as long as you can keep track of things later on. I
use an eraseable marker and a rule to scribe reference
lines on the monitor. Use a focal length that will
yield somewhere between 1 and 2 "/pixel. I found f/10
suitable for my 10" LX200 and CB245. You could
increase the focal length even more but you will find
this setup is extremely sensitive to movement and you
will overshoot if you make too big a step. After you
make a few adjustments take a ccd exposure noting the
location of a recognizable star then a minute or so
later take another and using an astrometry function in
any of the popular IP programs compute the star's
displacement. You can also simply get the (x,y)
location before and after and use the distance formula
to determine the pixel shift and use whatever
conversion that applies to obtain angular
displacemnet. Yes I know that stars travel in arcs but
with such small distances you can use a linear
approximation without sacrificing accuracy. I often
achieve a total drift between 25 and 35
arcseconds/hour or better.

Even if you do not use the indicators the ccd will
show you the drift much sooner so the wait between
adjustments can be dramatically shortened.

Again this may be a bit tedious but I found it a good
exercise for a bright moonlit night.

Regards,

Mike


> I have read your message and I am intrigued by your
> use of a CCD device and
> dial indicators to tweak the polar alignment. Do you
> think you could write a
> detailed procedure on how you accomplish this for
> all of us who are not as
> advanced? Thank you. Ettore
>
>
>


=====
Mike Fleenor

Fleenor Observatory
http://user.icx.net/~mfleenor/observatory/observatory_index.html

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