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Log Book Entry No.16
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Log Book Entry No.16
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Using a Bahtinov mask to find the focus:Based on Laurie's idea and this article![]() | ||||||||||
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< < | 3 images for each of the 48 moves made by the focuser. All the movements were 'in' moves of 250 steps. | |||||||||
> > | 3 images for each of the 48 moves made by the focuser. All the movements were 'in' moves of 250 steps. The images had a 5s exposure time and a master dark (made of 10 dark) was made and reduced from the images. | |||||||||
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> > | On each image, a gaussian was fitted to the brightest star (142/144 success) and the amplitude and sigma median were taken for each set of 3 images per focuser position.
The data was then plotted and assumed to be in a quadratic form. The results can be seen on the images below.
![]() ![]() ![]() While Sigma Y minimum is at: 5411 steps And the Amplitude maximum at: 6804 steps According to LogBookAstronomyEntry0015, the 2000 step (aprox 600µm) difference would be more than double the depth of field for the telescope (287µm on a f/10) ![]() A visual analysis of the graphs would suggest a minimum and a maximum for Sigma Y and the Amplitude close to 6000 steps and, visually, the image at step 5750 (image set 23) is the sharpest presenting a nice 'X' diffraction pattern produced by the Bahtinov mask. | |||||||||
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Log Book Entry No.16
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> > | Focus Theory![]() Basic FWHM and MaxPixel techniques ![]() Diffraction aids ![]() | |||||||
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> > | Using a Bahtinov mask to find the focus: | |||||||
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> > | Based on Laurie's idea and this article![]() 3 images for each of the 48 moves made by the focuser. All the movements were 'in' moves of 250 steps. | |||||||
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Log Book Entry No.16
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