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Pin-sharp stars, thanks to Mr. Bahtinov?

Posted: Mon Nov 16, 2009 5:07 pm
by rwilkinson
The eponymous Mr. B has developed a clever focussing aid which can be made with classic Blue Peter technology
(i.e cardboard and a sharp knife).
The Bahtinov Mask invented by Pavel Bahtinov, a respected Russian astro-photographer, will work with both kinds of camera (DSLR and astro-CCD) by producing a distinctive 'diffraction pattern' in a similar manner to the way a four vane secondary mirror spider vane on a Newtonian reflector produces a four pronged star and that of a three vaned spider vane produces a six pronged star. However, the unique design of the Bahtinov Mask produces a very bright image with a diffraction pattern forming a long cross comprised of two intersecting lines and a third line that moves across the centre of the cross as the telescope is adjusted in and out of focus. Correct focus is achieved when the centre line fits exactly in the centre of the cross.
Full details are here:
http://www.nightskyimages.co.uk/bahtinov_mask.htm