Rotation help

[Mav359]

Hi guys

im currently at Galloway. last night was clear so i was firing away and generally (apart from the wind) everything was ok, traking seemed ok. I had a go at the Iris nebula using my imaging rig & along side that at the same time my DSLR mounted to the top of the OTA was firing away.

The individual subs look ok but when i stack them i get major rotation in the picture. It occurs in both the DSLR & CCD shots.

why is this happening? The rest of my shots from the night dont have the issue.

Cheers

[Mav359]

Oh by the way i'm using Nebulosity to do my stacking & aligning, never had this before and as i say the other data doesn't suffer the issue. They are also only basic processed in Neb to show the error

[ronin]

May be stupid but when at Galloway have you changed the angle/latitude that the mount is set to.

Galloway should be 55.12 degrees.

Don't know your normal location but that could introduce an error that comes out as rotation as you would not, could not, be polar aligned

[msh1]

hi as your using nebulosity do you use the translation and rotation stack option??

[Uplooker]

May be stupid but when at Galloway have you changed the angle/latitude that the mount is set to.

Galloway should be 55.12 degrees.

Don't know your normal location but that could introduce an error that comes out as rotation as you would not, could not, be polar aligned

I would say it was closer to 54.831743,-4.425173. If that is what is causing the problem?

Ian

[Mav359]

Hi guys

My mount is polar aligned using Alignmaster,  i'll double check it but that semed fine when i did it.

In Neb i onbly use the translation to stack not translation and rotation, should i be? i never have before

[Mav359]

Yep translation and rotaion got it, is this because the target was near zenith?

[ChrisLX200]

Usually caused by inaccurate PA, the guider can correct (mostly) for the drift but can't do anything about rotation. If you did 30min subs they would be trailed, shorter subs won't look to bad but over time the rotation shows up - like when you stack.

ChrisH

[Mav359]

I'll double check the PA as soon as it clears, it was spot on but maybe i've moved something

[ollypenrice]

It's classic polar misalignment. As Chris says, you get away with it on shorter subs but unless you use translation and rotation stacking the rotation will appear in the stack. How bad it is depends on how far you are from the celestial north pole, so it will vary in severity between objects.

PA is easily nudged. Ground settlement?

Olly