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Old 15-11-2013, 08:22 AM
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pmrid (Peter)
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Join Date: May 2008
Location: Cloudy, light-polluted Bribie Is.
Posts: 3,665
"drift alignment " for a Polarie

Polaries don't have any ST4 input, don't track in Dec and have only a couple of fixed rates in RA. So how can you modify the usual drift alignment techniques to get around these limitations? Any ideas anyone?

The Polarie has a front plate that is attached to the drive mechanism via 2 pressure screws. The camera attaches to that plate. The Polarie also has a removable rear plate which (a) contains a small coarse compass and (b) allows a proprietary polarscope to be inserted through the body of the device and aligned with the asterism of the SCP's Octans group via a reticle. That is certainly going to give you a pretty good approximation of alignment. I'm not sure what sort of error would be the optimal result of that process.

But if you wanted to do exposures somewhat longer than 60-90 seconds at FLs of 200-300 or so, then you're going to want to pare back that error as much as possible. So how can it be done?

To start, you need the ability to take an image that is precisely on the RA axis - i.e. up that centre hole. I'm wondering whether it might be possible to butcher an old finder scope to fit over the RA drive spindle where the camera plate would usually be fastened. And if that is possible, whether it is also possible to engineer a simple holder for a guide camera at an appropriate distance back from the objective of the finder scope - but inserted through or into the back of the Polarie.

Assuming all this can be done, how then can you use it to make some meaningful measurement of error in both RA and Dec? If you can persuade Maxim to see your guide camera as Camera 1, it should be possible to take exposures of any length - say 5-10 minutes - over which time, a misalignment should show up as an extended line - the longer the line the greater the error. This would, of course be a single line and interpreting the length and angle of that line would be a bit of a trick because it would contain elements of error in both axes. But I'm sure it could be done so that over time, you could get the length of that line to the minimum possible - meaning the best alignment of which that system is capable.

Does anyone have any other hairyarsed ideas?

Peter
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