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Aligning my images with (compass) NORTH?


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Bit late to ask at this stage. My ignorance embarrasses me! :p

I know it "doesn't matter" really, BUT IF I WANT to have my
images orientated in a standard direction (e.g. North at top)
what do I need to do re. camera alignment? Can I just set it
parallel to "something" with the mount in HOME position...

Or is it more complicated? FIWIW, my setups often have a
"rotator" in front of the camera, so I can adjust things. But
so often I find they finally end up at a slightly odd angle! ;)

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From a solar imaging perspective, I use the NSO/GONG site GONG to orient my image.

That's not with the sun's north pole "up", as it is tilted relative to the Earth.  However, when comparing solar images, it seems to be pretty much "standard".

Clear Skies


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Rotating by 90 or 180 degrees is a one-click affair but will only lead to 'north is up' if the camera is orthogonal with RA and Dec. To make it so, just slew during a short exposure and look at the angle of the star trails. Rotate the camera until trails are horizontal or vertical. After that, take a quick shot of a target and see how it is orientated after pre-processing. Software does funny things to images. In Nebulosity on a Mac and, next to it, Artemis Capture on a PC, raw images from parallel scopes show the same orientation. Once opened in AstroArt the Mac images are flipped horizontal and rotated 180. Lord knows why, but since I know this I just two-click them to rights!


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Using the Quark in a refractor, straight through (no diagonal ) I fit the camera top up, square to the scope in the parked position, aimed south at 0 dec and the images come out more or less as the images on Gong using Firecapture so I don't usually bother to rotate them to get them just right.


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Belated thanks for all the contributions above! :)

Well done those who spotted that this was perhaps related
to my recent excursion into Solar Imaging with Lunt 50. ;)

I sususpect I was right - Simply aligning to the equatorial
mount axes, by sight or whatever. Indeed, I never had this
problem with the old night sky, the f/4 Newt and stuff. 

I sense the unexpected rotation (random 20 deg or so!) is
some function of the casual error in aligning both the pre-
and post-diagonal rotation (c.f. the "sweet spot" tuning!)
on the Lunt. Few square edges on either scope or camera!

The default of having a diagonal (sundry rotators) in the
optical path probably serve to exacerbate such things...
Now recalling (see school physics!) the "Optical Lever"? :D 


P.S. I suspect I meant celestial rather than compass north!

Edited by Macavity
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If you want to be exact, use Astrotortilla (other software is available) to plate solve.  It gives the rotation of the image, so you could adjust your camera until rotation is satisfactory.


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