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Using the camera to set up polar alignment and GoTo.

NOTE: The old version of this document is here: OLD VERSION

Pre-requisite: Polar Scope reticle, Imaging scope and RA axes are perfectly aligned. I use adjustment screws on the dove tail for this.

So, assuming the necessary steps have been taken to ensure the polar scope reticle, RA axis and scope axis are all in (very near) perfect alignment, the procedure step prior to image #1 is:
- start popping off 3 second frame and focus exposures
- center polaris in the Polar Scope's cross hair (dead center as opposed to it's Polaris ring)
- then move dec until Polaris is in the cross hair of the frame and focus window (now you know the camera and polar scope are aligned)
- adjust alt/az until the NCP is centered in the camera's crosshair.

A description of the pictures:
Images 1 and 2 are looking at axial alignment accuracy.
  • 01 Polaris.jpg - This picture shows Polaris (nearly) centered in the middle of the crosshairs and it is also (nearly) centered in the middle of the crosshairs of the Polar Scope (not shown).
  • 02 Polaris Arc.jpg - This picture shows close axial alignment between the RA axis of the mount and the imaging scope with a 180 degree rotation. Polaris moves some, but not too much.

  • Images 3 thru 7 are looking at polar aligning.
  • 03 Polar Alignment Polaris.jpg - This picture shows Polaris (nearly) centered in the middle of the crosshairs and it is also (nearly) centered in the middle of the crosshairs of the Polar Scope (not shown). This will be my starting position for star-hopping to the NCP.
  • 04 On The NCP.jpg - Though it may be hard to tell, the crosshairs are very close to the NCP here. The NCP is located nearly center and just off of an imaginary line between TYC4661-2-1 (9.6 mag) and TYC4643-26-1 (11.1 mag).
  • 04a On The NCP Labeled.jpg - This screenshot I took into Photoshop and labeled up a little. I can see that I am actually off by about 20 arcseconds, but then my axial alignment isn't 100% perfect either.
  • 05 180 Degree Test PA Very Close 1.jpg - In this picture I perform the 180 degree rotation test to see if the circles are concentric with Nebulosity's reticle. They are very close, but I make a small adjustment.
  • 06 180 Degree Test PA Very Close 2.jpg - The adjustment I made is a hair too much in the opposite direction and I get a very similar arc. Half of the adjustment may have been perfect, but I choose to leave it here.
  • 07 PA Off Example.jpg - This picture shows that when polar alignment is off, the circles become less and less concentric with the reticle. If you wanted to take the time to make minor adjustments until the star trails were perfectly concentric, you could, but I don't.

  • Images 8 thru 10 are the 1 Star Alignment process - the star is Capella.
  • 08 Alignment Star Capella.jpg - Without any adjustments, this is where the alignment process put Capella. You can see it's very close to center.
  • 09 Alignment Adjustment RA ONLY.jpg - By adjusting RA only I see Capella moving toward the center of the reticle.
  • 10 Alignment Adjustment RA ONLY.jpg - By adjusting RA only a bit further, I canplace it nearly dead center of the reticle. I made no Dec adjustments at all. This is another sign that Polar Alignment is *very* close.

  • Images 11 thru 15 show the actual GoTo call made via Starry Night Pro.
  • 11 SNP GoTo M51.jpg - Have Starry Night Pro tell the mount to GoTo M51. I chose M51 because it's 75 degrees and a meridian flip away from Capella. That's a long way to GoTo and try and stay close.
  • 12 Slew To M51.jpg - Probably pointless... it just shows slewing.
  • 13 Placement After GoTo.jpg - This is where my GoTo landed me. It's only off by 5 arcminutes. Pretty good for going to the other side of the sky on a one star alignment.
  • 14 Adjustment In SNP.jpg - This picture shows a 5 arcminute adjustment made in SNP to center M51 in the imaging scope.
  • 15 M51 Centered.jpg - This shows M51 successfully centered

  • Images 16 and 17 show guiding accuracy
  • 16 Guide Scope Alignment.jpg - I dind't include aligning the guide scope here, but you can see that, although the camera is rotated, the guide scope is poingint closely to where the imaging scope is pointing.
  • 17 Guiding Round Stars.jpg - The lousy seeing and clouds moving through compromize the clarity of the image, but you can see that the guiding averages 2/10 of a pixel of movement (the RMS value) and the stars in the M51 image, which is a 5 minute exposure, are round.

  • 01 Polaris.jpg   View   Download
    02 Polaris Arc.jpg   View   Download
    03 Polar Alignment Polaris.jpg   View   Download
    04 On The NCP.jpg   View   Download
    04a On The NCP Labeled.jpg   View   Download
    05 180 Degree Test PA Very Close 1.jpg   View   Download
    05a PA Very Close 1 Labeled.jpg   View   Download
    06 180 Degree Test PA Very Close 2.jpg   View   Download
    07 PA Off Example.jpg   View   Download
    07a PA Off Example Labeled.jpg   View   Download
    08 Alignment Star Capella.jpg   View   Download
    09 Alignment Adjustment RA ONLY.jpg   View   Download
    10 Alignment Star Centered RA ONLY.jpg   View   Download
    11 SNP GoTo M51.jpg   View   Download
    12 Slew To M51.jpg   View   Download
    13 Placement After GoTo.jpg   View   Download
    14 Adjustment In SNP.jpg   View   Download
    15 M51 Centered.jpg   View   Download
    16 Guide Scope Alignment.jpg   View   Download
    17 Guiding Round Stars.jpg   View   Download

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