Problem Calibrating On Single Star With Hi-Resolution Spectroscope

[Richard Brown]

I have a high resolution spectroscope and I would like to guide on a single star in the guiding module (235 mm focal length) for more precise guiding to keep the star in the slit. I unchecked the "Use Multiple Stars". When calibration starts there is clearly a problem-the mount starts in Dec then is erratic and eventually lose the star. I adjust the exposure and focus. and cables are secure. When I use the finder scope (60mm) it works but not as precise as I would like.

Richard

[Richard Brown]

Hi-I meant 235 mm diameter scope, not focal length-Richard

[Bruce Waddington]

In order to make any progress with this, you will need to correct a number of operational mistakes.  First, you keep talking about the diameter of the scope, which is not important in this context.  What matters is the focal length which you have configured as 2350 mm.  Is that correct?  Is this an f/10 optical system you have?  Assuming that's correct, here are the initial, basic problems:

1.  The system is under-sampled for guiding with a guider image scale of 0.21 arc-sec/px.  The new-profile-wizard would have warned you about that and advised you to bin the camera.  You need to do that.

2.   You're using guide camera exposures of 10-20ms which is basically ridiculous with this setup.  The SNR is very low and leads to constant lost-star conditions which is why your calibrations are so poor.  Even if you could find a suitably bright star, all you would be doing is chasing the seeing.

3.   As far as I can tell, you aren't using the Calibration Assistant to do calibrations, which is a mistake.  I can't know that for sure because you haven't uploaded both your guide and debug log files.  But I'm inferring that you aren't using the CA tool because you were pointing the scope down in the weeds in the western sky rather than in the recommended area for doing calibrations.

I think you need to set aside your spectroscopic interests for the moment and spend time getting all this sorted out.   The best way to move forward is to follow the attached guide for measuring your mount and guiding performance.  You should focus first on getting good calibrations using the Calibration Assistant - that starts with binning the guide camera and using rational exposure times of 1-2 seconds.  If you can't get a calibration that is judged to be at least "acceptable", your guiding results will be poor.  Going forward, when you want further advice on your situation, please follow the instructions for uploading you log files to our server:

https://openphdguiding.org/getting-help/

Regards,

Bruce