In a message dated 2/14/2008 10:36:37 AM Central Standard Time,
nitemike1@... writes:

I have had no problem with the calibration function of the ST4 as long as I
calibrate for about 10 seconds in both axis. When the guiding starts it
seems to work well for several minutes and then the numbers on the screen
progressively increase in the RA axis (as in periodic error).

1) In the old days when I was using one of these beasts, I figured out quite
quickly that I could not determine anything by looking at the numbers. I
placed a crosshair eyepiece on a seperate telescope, and while the ST4 was doing
its thing, I monitored the prosition of the star on the crosshair. So, if you
don't start out with this fundamental concept, you will probably be in the dark.
Start by watching the star motion when you calibrate. Is the star actually
moving in the 2 directions N-S and E-W? Next, press the 4 direction buttons.
Does the star actually move when you do this? If you don't do these things, then
you might as well forget trying to work with the ST4.

2) Your symptoms do not indicate periodic error. They do not indicate any
kind of mount electronics error besides maybe a slight polar misalignment (which
is not a mount problem). They indicate simply that the ST4 is probably not
sending any correction signals to the mount, and the star is simply drifting
slowly away from the center (stars will always drift for a variety of reasons not
related to the mount electronics, so this is quite normal).

Finally, your heading is misleading. It should not read "AP 900 Mount
problem", rather it should say "SBIG ST4 Problem".

Rolando


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