Lunar tracking rate

[Dawson]

I am told that on Skywatcher mounts , lunar tracking mode just tracks in RA, and makes no declination corrections, despite the Moon varying in declination by about 15 arcminutes or so per hour. Even with near perfect polar alignment the Moon will drift out of the FoV of the C14 with a large sensor camera on, in an hour, and for long imaging runs such as the lunar impact flash work, this is quite annoying.

Is there a reason why Skywatcher don’t / can’t add in some declincation correction?

Thanks.

James Dawson

[Dominic Ford]

Random guess: is this due to backlash? RA always moves in the same direction, so you can avoid backlash by always approaching targets from the east. The Moon’s declination moves in both directions, so there would be no way to completely avoid backlash.

[Nick James]

This is a hangover from the old days when mounts didn’t have motors on the dec axis and all you could do to track the sun and the moon was to change the RA axis drive rate to match their average eastward drift rate. Most mounts now have the ability to move in both axes and if you control them via software using, say, ASCOM or INDI, you should find that you can program offset rates based on the true ephemeris or, at least, some calculated offset rate. As Dominic says, there is usually some backlash in the gear system so that reversing direction is problematic but that is only really important for guiding, not in this case where any significant tracking offset is always in one direction.

[Robin Leadbeater]

My first goto, the Vixen skysensor 2000 happily did this and (tracked any other object) regardless of mount alignment. It came as a shock when I found this was not universally true !

[Dawson]

Thanks all.

I emailed OVL amd asked them, and they’ve contacted the engineers who replied with:

“We can confirm that we will add dual-axis tracking options to the SynScan Pro app for equatorial mounts in the future.”

So a) we’ll wait and see, and b) I better work out what the app is as I use the handset.

Thanks.

James

[Nick James]

If you use ASCOM/EQMOD the custom rates can be set for both axes in the “track rate” box. See attached pic.

Attachments:

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   eqmod.png
   

[Mr Jack Martin]

You’ll need a mini Mac to run the app.
I used my Samsung mobile, the screen is too small, its easy to press the wrong button, but it did fit the cradle of my Fusion 120i where the handset sits, I prefer the latter.
Regards,
Jack

[Nick James]

To be clear EQMOD is a Windows app under ASCOM although I think it might run under Linux with INDI. It is open source and has been around a long time so it is very stable. It uses a pseudo-serial interface either directly via USB for recent mounts or via a USB to serial cable for older mounts.

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