PMX assisance please

[cfranks]

I would really appreciate a little assistance with my MX. I have the MX on a permanent pier and remove the OTA when the sky won't be clear for a few days. It's located in my driveway in view of passing traffic. For an Imaging night, I reposition the OTA on the mount as closely as I can to its 'normal' position including rotation and balance. I have Polar aligned pretty well, within 0.0 Azimuth and 0.4 ticks on Elev. and have built a model accurate to 15 arc secs. My problem (currently) is what to do at 'switch on'. After Homing, do I Sync on a bright star and carry on or do I have to take a few more set-points and add them to the model?
Lots of strange things are happening at times which leaves me a bit confused. At the moment, I have had the OTA setup on the mount, under a TeleGizmos 365 cover, for a week as the nights have been reasonably good. Thursday was good and I switched off at 5 am. Friday I switched on , Homed and slewed to Rigel. It was more than 10 degrees off! Adjusted, Synched and went to another star. It too was way off. I then started from scratch and repeated a 100 point Auto calibration. Every Image link was perfect and the model was good to 16 arc secs. Switched Off, On and went through Startup again with the same massive error in alignment! I then rebooted the MX and everything went back to normal and the rest of the night was uneventful! :shrug: I would have thought that the initial Power On of the MX would have Booted the mount or am I wrong? :thanx:
Charles

[Mighty_oz]

That is a bit weired hey, should be same error i would have thought.
As for what u should do each time u put back the ota etc, see page 32 of the T-point manual here's a copy of the start of it.

" Using a Model from Night to Night
The nightly setup routine required for optimal TPoint-assisted pointing depends on
your observing setup and your hardware.

• For portable mounts, a new calibration run must be performed each time the
mount is setup.
• For permanent installations, a single model can be used each night.
However, in order to reuse a model, the physical setup of the mount cannot
change, precise equatorial coordinates of the mount must be restored from the
previous night’s observing session and an accurate time base must be used. "

So i would say start from scratch, if your doing a simple imaging run of 1 or 2 objects close than a short model may get u there. All depends upon how close u can set up the ota etc to where u took it off from.
Easier to run say a 50 point model while it gets dark waiting for imaging time.
Others with more experience i'm sure can give u a better idea, i'm new to this PMX thing as well.

Marcus.

[frolinmod]

Right, tearing down the scope and mount invalidates absolutely everything. All your calibration work is for naught when you do that. You can calibrate from scratch again every night, but it'll kill an hour or two every night at the very least, even after you get really good at it. You could possibly recalibrate instead of calibrate if you find the actual model terms don't change night to night, just the values of the terms. That would allow you to use fewer points and shave a little time off. You're likely not going to benefit much from an MX and hardly at all from Tpoint unless you can leave things set up for at least a few days at a time, such as in a back yard or a campsite covered with a Telegizmos 365.

[cfranks]

Thanks for the replies.

The mount is never (so far) disturbed, only the OTA but I will try the short Tpoint run. That really weird error on Friday was without the mount nor the OTA being disturbed for a week. Just being switched off and covered each morning. I think it should be reasonably clear tonight for a short while so I will see what happens.

Charles

[cventer]

Charles,

If your polar alignment is good enough you dont even need a t-point model to just get objects into fov. (depending of course on how small your fov is)

I have not added a t-pointg model to mine for months now. I just home and then do a goto. Image is allways within my fov. I just jog control to center it.

I did do a long t-pont run and after that it was dead center but after some mount tweaks i never had time to redo the pointing model.

Some tape and pencil marks should help get ota to same spot in the MX clamps which wil help with repeatable pointing but you will never get to the pointing this mount is capable of if you slide of the ota every night.