My Tpoint model with with 150 points performs well except that the target is moderately offset from the center of FOVI by nearly the same amount throughout the sky. This can be attributed to the imperfection in my Tpoint model itself, the adding of AO8, Pyxis Rotator, etc to the image train thus altering the optical axis after finalizing the Tpoint model, etc.

This offset interferes with my target planning in Autopilot4 when determining the position and PA of guidestars.

Can I correct this without doing a new Tpoint modelling ?

1. by manipulating the default.mks file of ME in TheSky Pro, such as adjusting the HA/DEC values in the home sensor position ?

2. by keying in some 'offset' figures in the FOVI settings in TheSky Pro ?

3. by physically manipulating the image train itself ?

4. by keying in some offset figure in AP4 ?

Any other suggestions ?

Regards,

Stewart

Hi Stewart,

The pointing error you are seeing is not an issue when framing your target. Simply move the FOVI to where you want it to be, use Get and enable Precision Slew on the target page. The coordinates of your target will be brought into the target list. Precision Slew will slew the telescope to the target position, do a plate solve to find out exactly where it is and adjust the pointing to insure the target is close. By enabling a tolerance, say 20 arc-sec., up to three tries will be used to get within that tolerance.

If the offset bothers you, you can always do an image link and sync into the existing model. Also, if the offset is predominantly in RA, check your PC clock. 1 minute of time error is equivalent to 1/4 degree in the sky!

quote:

Originally posted by John Smith:

"move the FOVI to where you want it to be, use Get and enable Precision Slew on the target page. The coordinates of your target will be brought into the target list. Precision Slew will slew the telescope to the target position, do a plate solve to find out exactly where it is and adjust the pointing to insure the target is close. "

This doesn't seem to to work. The final image I got is still offset.

I don't know why, but what could be wrong so that the target didn't get corrected in position ?

Regards,
Stewart

Hi Stewart,

When you say the final image is offset, do you mean in TheSky6 or the actual image that is downloaded from the camera?

I mean the taken image.

The "get" operation didn't seem to shift the camera to the position and PA performed by me (by clicking at the FOVI, clicking to "translate" and "rotate" the FOVI).The taken image had not been centered by my "translational" operatoin in "get" , and the intended guidestar didn't seem to be centered in the self-guider by my "rotate" operation in "get".

I guess I've missed something so that the "get" didn't work.

Stewart,

All "Get" does is Get the RA, Dec. and PA of the FOVI and enter it in the target list. To actually move to the target FOVI, hit the Slew To Target button.

Of course I 'run session" when getting the image so the "slew" step had been involved.

Incidentally, do I have to "center" the FOVI before I "translate" and "rotate" it ? Does it make any difference if I haven't center it first ?

Please post a log of the session with the problem.

Hi John,

It seems that my main problem is capturing the guidestar. I've got my Pyxis' home position at 270 deg relative to the FOVI and I am confused about how to reconcile this offset in AP4. The PA always gets wrong as I observed the AP4 sessions running.

Here are my log files on 5Nov:

ccdap20091105_210606.log (29 KB, 4 downloads)

Hi John,

More logs :

ccdap20091105_204711.log (12 KB, 4 downloads)

Hi,

Aborted run as the guidestar didn't turn up :

ccdap20091105_230905.log (7 KB, 1 downloads)

Hi Stewart,

One of the first things I notice in your log file is that your plate solves are failing. When this happens, CCDAP4 can't determine the PA so where it ends up is usually where it started off. I would suggest that you investigate the cause of the plate solve failures and get that resolved first. I also notice that your RoBoFocus is using " FocusMax is using the RoboFocusDummy.Focuser focuser driver" My experience has been that this is not a reliable driver and the ASCOM version works much better. HTH ....

[QUOTE]plate solves are failing.

Yes, whenever the targets are star clusters like M15 plate solve usually failed. For star fields such as M52 it would be all right.

Why ?

Hi Stewart,

Star Clusters are sometimes difficult to plate solve for due to the density of the stars in the center of the cluster. It could also be partly due to the star catalogs that might be active on your system. One thing you could try is to start with just the GSC catalog active in TheSky6 and if that fails, add another catalog to see if the plate solving completes successfully. I find that the GSC catalog is adequate most of the time, but in some regions of the sky I need to activate the UCAC2 catalog to get reliable plate solves. HTH .....

[QUOTE]It could also be partly due to the star catalogs that might be active on your system. QUOTE]

I've already activated the GSC, UCAC2, and also USNO B1.0.

To get to the root of the problem : is AP4 offering the option of NOT doing plate solving for some targets ?

My TPoint is sufficiently accurate that a precision slew may not be necessary.

Can one set the PA for a guidestar without doing plate solving first ?