[PRejto (Peter)]

Hello,

I'm having an issue with my PMX that I cannot seem to resolve. In this setup I'm guiding with an ST-i through an 80 mm APO mounted firmly on top of my TEC140. I seem to get good results in RA but DEC is a problem. I have adjusted the cam stop but the behavior persists. As the picture shows below RA is roughly aligned with "X." Guiding usually starts off well in both RA and DEC, but after ca 2 minutes I will get a relatively large error in DEC that does not correct for a long time. Exposures were 6 seconds long and correction does not begin until after a minute of error (or so it seems to me). Aggression was set at "6." When I increase aggression to "7" guiding in DEC improves but the corrections in RA are then too aggressive. Through experimentation it does seem that I generally need to increase aggression when I have longer exposures. With dim guide stars I need longer exposures and this is when my problems start.

If I restart guiding with DEC (Y) corrections turned off I will track very well in DEC for about 3 minutes followed by errors in the +Y direction, so that is the way DEC is drifting with time.

Is there an adjustment that anyone might recommend to improve DEC guiding without sacrificing RA guiding? Would a change to motor speed in DEC through the Bisque TC have a bearing here? Do I need "backlash" compensation? (I would think not because during calibration the mount appears to respond immediately in DEC.)

I cannot find any free play in the guide scope though I suppose that possibility cannot be discounted entirely. It does seem odd to me that the error(s) are only in DEC however. I would imagine that movement of the guide scope would be more random and less predictable. I can try to eliminate that possibility by re-setting up the ONAG guider, but would prefer not to at this time.

Any help will be very much appreciated!

Peter