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Polar Alignment Tool

EQMac includes a polar alignment utility designed to help you achieve a more precise alignment. It will not be as precise as performing a Drift Alignment, but it will be good enough for observing and perhaps good enough for imaging depending on how you feel about polar alignment accuracy.

To use the polar alignment tool, it must first be calibrated. The goal of calibration is to let EQMac understand the positioning of your polarscope reticle, particularly the position of the small circle into which you will ultimately place Polaris. EQMac needs to know how far to rotate the RA axis to place the small circle at a known reference position. Once it has this information, it can compute the exact location of Polaris and rotate the RA axis so that the small circle is in exactly the right place.

To get started, let's assume that you have your mount in the home position and that you do not have a scope or counterweights attached. This is important because during polar alignment, the RA axis could be rotated up to 180 degrees away from home, and if you had a scope attached when that happened....well, <clang>, <tinkle>, <tears>.

Your first step is to determine the nearest reference point to the Polaris circle for your mount. EQMac will allow you to set the reference point to 12 o'clock, 3 o'clock, 6 o'clock, or 9 o'clock. So, with the mount in the home position, and the DEC axis possibly rotated 90 degrees to enable views through the polarscope, have a look at the position of the small Polaris circle and determine to which reference position on an imaginary clock face the circle is nearest. For example, if you see the circle is roughly at the 2 o'clock position, then you might choose 3 o'clock as the reference point because that would require the least rotation of the RA axis from home to place the Polaris circle at the reference point. Alternatively, if the circle is sitting at say 7 o'clock, then you might choose 6 o'clock as the appropriate reference. Every mount is different because the polarscope reticle will be randomly positioned during the assembly process.

For the benefit of explanation, I will assume that you have chosen 6 o'clock as your reference point. The next step is to use the latitude and longitude adjustment bolts to position Polaris at the centre of the crosshairs in the middle of the large circle around which the smaller circle rotates. When Polaris is positioned in this way, use the appropriate adjustment bolt to move Polaris into the reference position that you have just chosen on the circumference of the larger circle. So in our example, we would use only the latitude bolts to move Polaris down to the 6 o'clock position sitting exactly on the outline of the larger circle. Once you have done this, use Polaris as your guide to slew the mount in RA until the small Polaris circle is also in the reference position exactly covering Polaris.

When you are happy that both Polaris and the small Polaris circle are in your chosen reference position, click the Calibrate... button in the Polar Alignment window. EQMac will record the current position of the mount (including the DEC axis) for use in future alignment sessions. The calibration is now complete and will not need to be performed again provided that you do not release the clutches and alter the position of the mount manually. If you cannot avoid this due to having a portable setup, then you will need to perform the calibration steps each time.

Once calibration is complete, all you need to do is click the Align Polarscope button and EQMac will rotate the mount in RA until the small Polaris circle is in exactly the right position for polar alignment. Once the alignment slew completes, the mount will begin tracking so that the small circle stays in the correct position while you perform the actual polar alignment. Not that Polaris would move much during that time, but every little helps as they say.

When EQMac has aligned the small Polaris circle, use the latitude and longitude adjustment bolts to place Polaris inside the small circle. Once you are happy with the positioning, click the Move to Home button and your polar alignment is complete. You can load up the scope and counterweights and begin your session.