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Focusing on Mizar with a Bahtinov mask

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I'm finding it particularly helpful to point the scope at Mizar in the Plough/Great Bear, when I want to adjust focus. You get three stars of various 'sizes' and hence three diffraction patterns to judge focus by. Mizar (Magn +2.22) is already a double with a separation of a bit less than an arc second, but in the field of view you also have Alcor (Magn +4.00), another double, and in between HD 116798 (Magn +7.78). This makes the Bahtinov diffraction pattern interesting - and I find the best precision if I refer to the tiny diffraction spikes around HD 116798.


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