Updated Celestron driver

I’ve updated the ASCOM driver for the Celestron telescopes to avoid the error in slews that has been a source of considerable trouble for pointing accuracy for years. This driver measures the difference between the slew target and the position the mount reaches and applies that difference to subsequent slews. The result is that the position reached should be closer to what is required.

It’s on its way to the ASCOM site but if anyone wants a preview the installer is on Dropbox here:

As a user you need to do nothing. The driver handles it transparently.

The reason for the error is that Celestron were not allowing for the time that their slow final approach slew was taking so the mount always ended up as a reported position that was a few seconds behind the sky. The final slew is always about the same distance and time so the error is consistent. I’ve been hoping I could persuade Celestron to fix this.

As always, if you think this is causing problems let me know and include driver logs showing the problem.


Hi Chris,

Thanks for the updated driver. I’m going to give it a try tonight. supposed to be a clear night tonight and will let you know how it goes. BTW, all I need to do is to run the executable and it will install the new driver and overwrite the old driver, correct?

Kind Regards,

Correct. I responded by email a few hours ago and had a reply scolding me for using too short a reply. Yet another robot failing the Turing test.

I just updated the driver and plan to image tonight, so can report back any issues. So far the only thing I noticed was my parked position in ASCOM for the “old” driver did not transfer to the new one. So I just set it again and should be good to go.

Update: everything worked great last night. Woke up this morning and the scope was in the parked position with a disk full of good data.

Were you getting better pointing accuracy using the normal solve, sync and slew centering method? I’d expect that the Ra part of the pointing error should be considerably reduced.

Hi Chris,

I was able to test out and use the Celestron Driver last night. It definitely improved the pointing accuracy on the CGEM-DX. I was not able to use it on my CGE-Pro. My CGE-Pro is currently down for some maintenance work I needed to do.

Below is my summary of some testing I did last night.
Image scale is 0.75"/Pixel. With the old driver I would typically have my error tolerance set to 80 pixels in SGPro and would typically achieve in the low 70 pixels in 3 iterations. With your new driver I found I can set the error tolerance to 40 pixels and would achieve in the mid to low 30 pixels in 2 or 3 iterations. I think I can get better pointing accuracy if I lower the tolerance and let it do more iterations but with my image scale I think the 30 pixel is more than perfect for my needs. Law of diminishing return, lowering the tolerance below 40 doesn’t seem to be worth the time. At my image scale 40 pixels max would give me a total pointing error of only 30 arc-seconds max.

Thanks for working on the new driver. As always your work is always appreciated,

I believe the pointing accuracy on my CGE-Pro was improved. Though I imaged on M82 all night long so my sampling size for pointing is small. I am planning another imaging run with M82 tonight. But I did note that the centering was done in two steps: initial slew and then one refinement.

Thanks for the feed back. Good to hear that the pointing is better in real life.
30" is less than the diameter of Jupiter.