Why am I seeing field rotation?

[Peje]

2 minutes ago, RayD said:

Yes you will have a cone, but it is only relative to where you think you are pointing, and where you actually are. 

For example, forget targets, just bolt everything together and have a perfect PA, now don't do any star alignments, just turn your mount on, start imaging and tracking at whatever your telescope is pointing at, which of course could be no target at all as your mount is aligned with polaris, but your telescope isn't.  So long as your PA is perfect you should be able to image that same target all the way through 360 degrees without it moving from the centre of the camera, which according to the video it would do.

I need to do some experiments with this as I reckon I'm missing something and wrongly simplifying it.

I see what you're saying, I have a feeling Dec is what screws it up. Your mount will adjust Dec to compensate for some PA error and that might mean the circle will no longer track the object... shooting from the hip a bit there.

[RayD]

I think with your issue we need to separate cone error and orthogonality.  If you have a cone error and you are imaging with guiding, it should make no difference, but if you camera is not orthogonal to the RA axis, then after a meridian flip you can get what is showing in your image.  If you are perfectly orthogonal your image will still be be upside down of course. 

[Peje]

3 minutes ago, RayD said:

I think with your issue we need to separate cone error and orthogonality.  If you have a cone error and you are imaging with guiding, it should make no difference, but if you camera is not orthogonal to the RA axis, then after a meridian flip you can get what is showing in your image.  If you are perfectly orthogonal your image will still be be upside down of course. 

Ok, I accept I may have two separate issues.

If cone error was corrected, would that not make the other less troublesome? It seems that in a perfect world orthogonality should not matter.

Looking forward to fixing the cone error now as it seems some simple to do with the software I mentioned earlier.

[RayD]

2 minutes ago, Peje said:

Ok, I accept I may have two separate issues.

If cone error was corrected, would that not make the other less troublesome? It seems that in a perfect world orthogonality should not matter.

Looking forward to fixing the cone error now as it seems some simple to do with the software I mentioned earlier.

 Yes you're right it can't hurt to correct it if it is easy enough to do.

I think the orthogonality is only critical for getting your camera back in the same position time after time and not having to crop chunks off your images and shouldn't actually cause your issue, which does seem like something is actually moving.

I'm going for a lie down now 

[RayD]

Don't forget to check your alignment after the flip though as mentioned in an earlier post.  If you are not getting back to the same spot, then imaging the other side of the pier and stacking the images, this could cause the image you posted (coupled with the camera not being orthogonal to the RA axis).

[Peje]

OK so I think I've found a hole in my plan...

The instructions for cone sharp say to pick a star with Declination close to zero, this means horizon rather than celestial equator doesn't it? If yes, dang! I have an obstruction to about 15 degrees

EDIT: Wiki to the rescue. Dec Zero = Celestial Equator. I'm good

Wiki: Declination

[Peje]

4 hours ago, RayD said:

Don't forget to check your alignment after the flip though as mentioned in an earlier post.  If you are not getting back to the same spot, then imaging the other side of the pier and stacking the images, this could cause the image you posted (coupled with the camera not being orthogonal to the RA axis).

Just incase I misunderstood, you basically mean run a plate solve after the flip? Thankfully SG Pro does this for me

[RayD]

15 minutes ago, Peje said:

Just incase I misunderstood, you basically mean run a plate solve after the flip? Thankfully SG Pro does this for me

That's is Pete. Just check that your tolerance is pretty good, somewhere around 20 pixels or less. If it's up too high it can mean you have to crop loads off. 

[Peje]

Mine is currently set to 100 pixels, with 3 attempts to hit it.

[RayD]

9 minutes ago, Peje said:

Mine is currently set to 100 pixels, with 3 attempts to hit it.

Wow that's pretty high Pete. Try to get that as low as your mount will allow. I'd start at 50 and try reducing in steps from there. 

Also if you are using EQMOD make sure it is set to dialogue mode as append to synch causes issues with the automated flip. 

[Peje]

Thanks, it is set to dialogue mode. Not sure about the other one, it's never failed to do a flip in the last 3 years so I'd imagine EQMOD settings are good.

Good idea on the error, I'll set it to 50 and allow 5 attempts.

[RayD]

13 minutes ago, Peje said:

Thanks, it is set to dialogue mode. Not sure about the other one, it's never failed to do a flip in the last 3 years so I'd imagine EQMOD settings are good.

Good idea on the error, I'll set it to 50 and allow 5 attempts.

Good stuff.

Mine is set to 3 attempt at 20 pixels and never fails, so don't be afraid to push it down as the lower this is the better aligned you'll be and the less cropping you'll be doing.