You have missed the point entirely.
Autoguiders etc are only useful for tracking an object once it has been
acquired.
Pointing is the ability to point the telescope at a desired object or
location starting from home or another position in the sky.
With large telescopes (or with inexperienced operators) one doesnt have
the time for manual correction.
It is desirable to place the object of interest close to the centre of
the field.
Once it is acquired then use of autoguiders and periodic error
correction (an open loop process) can be used to track the object.
When cloud cover permits, a wide angle (8 to 15 degree FOV) camera fixed
to the telescope can be used to implement a high accuracy (1 arc sec or
so) "encoder".
Bruce
J. Forster wrote:
These are all OPEN LOOP corrections. They are better than nothing, but
nowhere near as good as properly implemented auto-guiding which is closed
loop.
They are certainly not as good as even the simplest Adaptive Optics
utilizing only a Tip-Tilt tracker.
-John
==================
One needs to know the local apparent sidereal time to aid initial
acquisition of the target.
Periodic error correction and using an autoguider are of little or no
use for this operation.
However correction for encoder error axis non orthogonality, encoder
eccentricity and bending of the telescope tube an the mount may be
required.
A pointing model for the telescope is derived from the pointing (not
tracking errors) errors for a set of target objects uniformly
distributed over the sky.
For further details see:
http://www.tpsoft.demon.co.uk/
Bruce
Jim King wrote:
I'm not sure your friend needs the time at all. Telescope tracking
mounts have a periodic error due to non-perfect mechanical parts. The
usual way to remove this error is to "train" the mount by manually
guiding it through one or more periods, or - probably more common
these days - use an optical autoguider.
Jim
On 1:59 PM, Brooke Clarke wrote:
Hi Brian:
Why? Do you just want to see the sidereal time on a display or do
you need a digital output?
The Spark Fun "serial enabled" displays use what's called a "back
pack" that has the PIC 16F88 uC and it's used to do serial data to
LCD parallel data can control lines. I've made some clocks using
that chip.
http://www.prc68.com/I/PIC16F88.shtml
http://www.prc68.com/I/PRC68COM.shtml#07092006
A friend is setting up an observatory where the pointing accuracy of
the telescope mount is specified as " 7 arcseconds or less
peak-to-peak periodic error before correction". Much better after
correction. That implies he needs to know what time it is within
tens of milliseconds.
http://www.prc68.com/I/StellarTime.shtml#StrMov
We looked into different ways to get the time into his computer to
that accuracy and NTP looks like it will fill the bill, so a GPS
receiver may not be required.
Have Fun,
Brooke Clarke
http://www.PRC68.com
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