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    Re: Back sights, a working Virtual Octant
    From: Brad Morris
    Date: 2010 Apr 1, 12:40 -0700

    A while back, George and I were mildly debating the optical path for a backsight octant. I provided a hand-sketch, which seemed to imply that, for parallel path optics, a very long index mirror would be needed. Although I did mention that the diagram was not optimized, that wasn't inherently clear in my communications.

    Attached herein find two versions (.xlsx and .xls) of a virtual octant. You can move the angles of the horizon mirrors, the index mirror, the locations of various mirrors and the length of the index mirror. It will permit you to arrange the mirrors in a way that you think is best. The power is now in your hands to 'design your octant' optimizing for backsights or whatever you want.

    All the normal rules of reflection work. The mirrors are treated as front surface mirrors, without regard to Snell's law for a backsurface mirror.

    I think you will find that there are several configurations that work and that the length of the index mirror is function of the placement of the two horizon mirrors, among other things.

    I will probably go ahead and generate one for the case where the optical path for each horizon mirror strikes the index mirror in the same location. That will be just a bit trickier, because if we move the mirror in X,Y we must also change the angle. I wonder if that should be automatically done....

    Best Regards

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