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The mathematics behind designing polar alignment reticules


Ajohn

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Some time ago I saw details on this but can't currently find any at all. There is one web site that seems to measure positions of stars actually through a telescope in order to make one.  It's essentially a matter of angles, the focal length of the lens sets the scale.

Does anyone know of a source of the information that is needed?

The web is rather clogged up with using them rather than any information like this.

John

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  • 2 weeks later...

I'm working on a polar alignment 'scope idea and may be of help. I don't have the ability to make a reticle and plan to replace it with an offset crosshair in the centre of a disk with RA markings. One crosshair will span the hole in the centre along RA 2h 31.82m. The other crosshair will be offset from the centre by the focal length * tan(90* - 89* 15.843'). The other stars (Big Dipper/Cassiopeia) on a reticle are not to scale and only there to bring local sidereal time into play. Working on an Arduino sidereal clock/spirit level to solve that for me at the moment.

This drawing illustrates the principle of what I want to do. The RA disc is mirrored for use with a diagonal as I'm not fond of muddy knees.

 

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Thanks for that. I've wondered about making a reticule using a milling machine to generate the co ordinate - but not entirely sure how I would make the marks - yet. Maybe rotate a sharp carbide scriber by hand, black the lot and then clean off leaving the dots.

I may have a book on it's way from the USA with it all laid out. I have seen it some where but not sure where. I'll photo copy the details and post them if they are in it.

Meade produced a right angled finder with the reticule in it. That may prove to be the easiest way to go in some ways but the finder needs to be aligned to the mount not the scope.

I entirely agree about muddy knees. I have a mount now where even getting them wouldn't help. I can make something to easily attach a camera right angled finder to it but wonder why they don't provide one. :happy11: Maybe Gina will start printing and selling them. Canon fitting would be favourite.

John

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