Autoguiding horrendously misaligned mounts

[Garbz (Chris)]

They say there's no such thing as a stupid question. Let's give that theory a try shall we?

Is it possible to somehow achieve guiding on an equatorial mount which is misaligned?
I should mention my specific application, today I was doing Comet C/2012 F6 Lemmon while it was immediately beneath the south celestial pole in the Octans.

Naturally right underneath the pole is not a position I can put my mount into. Not everything is as upside down in Australia as the northern hemispherians like to believe and my mount was certainly not attached to the ceiling.

Anyway I eventually got my comet photos unguided without tracking and by limiting my exposure times to 5 seconds. I know. What's worse is how I found the damn comet. I pointed straight above it using the computer, measured how many degrees down the scope needs to go and adjusted the altitude screw on my mount.

Anyway here we are not only are we not aligned to the south celestial pole but sidereal tracking would actually go backwards given how I've just set up my scope. And naturally PHD had a meltdown.

So with that in mind is there anyway software, or technique or otherwise to track something below the south celestial pole other than using some magic floating plinth for the equatorial mount?

Cheers.

[ZeroID (Brent)]

IF, and it's a big IF, your mount is perfectly aligned with the SCP axis and there is no cone error between scope and said axis then theoretically, given the distances involved, that IF the scope is in that position the scope should go round and round forever and still look at the SCP.
I told you there was a lot of IFs..
In reality though .... viewing\imaging near the SCP can be a real PITA even if the above setup is perfect.

[Steffen]

As Brent said, pointing to below the SCP shouldn't be an issue, if the mount is polar aligned. I have no idea whether tracking with precision is possible/easy, ignorance is the bliss of the visual-only astronomer

What I wonder though is: From what I've read the comet has got some fairly large proper motion, will sidereal tracking be enough to follow it around for the purpose of imaging?

Cheers
Steffen.

[jjjnettie (Jeanette)]

It's a right PITA to get centred isn't it. I was cursing and swearing like crazy last night.
Good luck.

[Garbz (Chris)]

Just to clarify it was impossible in this case to point directly at the SCP. The target I was shooting was lower in the sky than the pole, as such I would need a magical upside down tripod lest my scope has an unfortunate meeting with the tripod legs.

In my scenario last night where I aimed the scope below the SCP on purpose guiding would have been in the opposite direction at the very least. I.e. I was trying to turn clockwise from east to west while my target (under the pole) was moving from west to east.

I gave up trying to set my sideal rate in reverse not that it would have helped anyway and instead turned it off completely.

However ...

With guiding you're effectively adjusting what a scope is doing against an X-Y grid. I don't understand why the autoguider can't have guided on a target anyway, simply because it was reversed.

My only conclusion is that the guider won't move the mount fast enough since it was designed for minor adjustments rather than compensating for lack of sidreal tracking. In any case PHD calibrated ok but then went mental when guiding latching both RA and DEC outputs and very quickly lost the target (faster than not tracking at all )

[Steffen]

If the mount is polar aligned then in its home position (scope parallel to the mount's RA axis) it will point straight at the SCP. It will do so at any RA position, you can swing it around the RA axis and it will keep pointing at the SCP (assuming no cone error). To point it below the SCP you just swing it around the RA axis 6 hours (90 degrees) to the left or right, then use DEC to go down to your target.

Cheers
Steffen.

[Garbz (Chris)]

*FACEPALM*

So yes there is such a thing as a stupid question.

Clearly it was past my bedtime when I was taking a photo of Lemmon. You're absolutely right I got my RA and DEC axis confused. Just looking at a map of the sky right now it should be obvious that the entire horizon can be seen without the RA axis ever actually going below 90deg

Thanks Steffen

Move along people nothing to see here

[AstroJunk (Jonathan)]

Originally Posted by Garbz

Move along people nothing to see here

Just having a rubber neck