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Bahtinov Mask - Double Stars
All the discussions and work being done on the Bahtinov mask reminded me of the diffraction mask/ grating used by double star observers.
By putting a grid across the objective a star image is broken down and secondary images are produced either side of the primary Zero image. This is well seen in some of the Bahtinov focus images.
By applying a mask to double stars, the known angular distance between the Zero and subsequent images can be used to measure the separation between the components.
The distance (in arc seconds) is 206265 * lamda/P where lamda is the wavelength of light being observed and P is the spacing of the bars (one bar and one space). For green light and P=10mm, the distance is 11.6 arc seconds.
Martinez in "The Observer's Guide to Astronomy, Vol2, p734 explains and shows examples.
Well work trying, CCD images would make the analysis even easier than visually.
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