Problems with AutoGuiding

On January 10, 2001, under a full moon, I pointed the NGT-18 into the double cluster to image to take a quick one second image of NGC 0884 using the ST-9E.  I did this with the following result:  I hadn't taken the time to do a good polar alignment, although I was probably within one degree of the pole, or maybe a bit better.  I took the quick one second exposure shown below.

I had been having problems with the ST-9 and the NGT-18 getting the autoguider calibration to work..  The X and Y movements looked crazy.  For example, a movement of the X axis would show movementg in both the X and the Y directions.  This movement would cause the software to declare defeat and give up with a message like "invalid movement in the X or Y axis".

After asking the question of a couple of news groups, the concensus seemed to be that the camera was not correctly aligned to the scope.  So I aligned and re-aligned the camera on the scope, all with the same effect.  I could not get calibration to work no matter what I did.

Then I took the image shown above, and attempted to determine just how deep a 1 second exposure could go.  As a part of this analysis, I did an image-link using Software Bisque's TheSky and produced the image shown below.  Again I made sure the camera was mounted properly along the axis of the scope.

When the image-link was finished, I noticed the direction of North on the image was not "up", but rather 19 degrees or so to the left.  I know that the camera was arranged vertically with respect to the optical axis of the scope.  What was puzzeling was how the North axis could be so far off.  (The vertical white line represents the angle of the detector (telescope axis), and the white line on the angle represents celestial north).  This error I would have quickely seen.

Two days later, it hit me what the problem must surely be.  The nose of the NGT-18 rotates.  The nose rotates to provide a good visual viewing angle for the eyepiece, but when the rotation takes place, the field of view is rotated as well, and a rotation through 90 degrees of the nose will rotate the XY orientation of the camera by 90 degrees as well.

This I did not know, but the orientation of the image above pretty much proves that it occurs.