Difference: LogBookAstronomyEntry0016 (1 vs. 4)

Revision 427 Sep 2013 - PedroPaiva

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META TOPICPARENT name="LogBookAstronomy"

Log Book Entry No.16

Days, Calendar Created: 24 Sep 2013 17:09:04 Days, Calendar Last Revised: 27 Sep 2013 13:31:23 Person PedroPaiva Text Focus Study (Pt II)
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  • Animation showing star going into and out of focus (with Bahtinov mask):
    focus_stern.gif
 
META FORM name="%25SYSTEMWEB%25.LogBookForm"
FORM FIELD Subject Subject Focus Study (Pt II)
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META FILEATTACHMENT attachment="Amp.png" attr="h" comment="" date="1380130754" name="Amp.png" path="Amp.png" size="59677" user="wxqv038" version="1"
META FILEATTACHMENT attachment="SigX.png" attr="h" comment="" date="1380130754" name="SigX.png" path="SigX.png" size="46989" user="wxqv038" version="1"
META FILEATTACHMENT attachment="SigY.png" attr="h" comment="" date="1380130754" name="SigY.png" path="SigY.png" size="41047" user="wxqv038" version="1"
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META FILEATTACHMENT attachment="focus_stern.gif" attr="" comment="Animation showing star going into and out of focus (with Bahtinov mask)" date="1380285082" name="focus_stern.gif" path="focus_stern.gif" size="5186311" user="wxqv038" version="1"

Revision 325 Sep 2013 - PedroPaiva

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META TOPICPARENT name="LogBookAstronomy"

Log Book Entry No.16

Days, Calendar Created: 24 Sep 2013 17:09:04 Days, Calendar Last Revised: 27 Sep 2013 13:31:23 Person PedroPaiva Text Focus Study (Pt II)
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Using a Bahtinov mask to find the focus:

Based on Laurie's idea and this article a set of 144 images were taken.

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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.
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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.
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.

SigX.png

SigY.png

Amp.png

For the Sigma X values, the minimum can be found at: 4841 steps
While Sigma Y minimum is at: 5411 steps
And the Amplitude maximum at: 6804 steps

According to LogBookAstronomyEntry0015, the 2000 step (aprox 600Ám) difference would be more than double the depth of field for the telescope (287Ám 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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FORM FIELD Subject Subject Focus Study (Pt II)
FORM FIELD Status Status blank
FORM FIELD Author Author PedroDeCarvalhoPaiva
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META FILEATTACHMENT attachment="Amp.png" attr="h" comment="" date="1380130754" name="Amp.png" path="Amp.png" size="59677" user="wxqv038" version="1"
META FILEATTACHMENT attachment="SigX.png" attr="h" comment="" date="1380130754" name="SigX.png" path="SigX.png" size="46989" user="wxqv038" version="1"
META FILEATTACHMENT attachment="SigY.png" attr="h" comment="" date="1380130754" name="SigY.png" path="SigY.png" size="41047" user="wxqv038" version="1"

Revision 225 Sep 2013 - PedroPaiva

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META TOPICPARENT name="LogBookAstronomy"

Log Book Entry No.16

Days, Calendar Created: 24 Sep 2013 17:09:04 Days, Calendar Last Revised: 27 Sep 2013 13:31:23 Person PedroPaiva Text Focus Study (Pt II)
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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:

 
Added:
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Based on Laurie's idea and this article a set of 144 images were taken.
3 images for each of the 48 moves made by the focuser. All the movements were 'in' moves of 250 steps.

 Back to: LogBookAstronomy

META FORM name="%25SYSTEMWEB%25.LogBookForm"

Revision 124 Sep 2013 - PedroPaiva

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META TOPICPARENT name="LogBookAstronomy"

Log Book Entry No.16

Days, Calendar Created: 24 Sep 2013 17:09:04 Days, Calendar Last Revised: 27 Sep 2013 13:31:23 Person PedroPaiva Text Focus Study (Pt II)

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  • Set EDITMETHOD = wysiwyg
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IDEA! Please edit and put your text etc. here

Back to: LogBookAstronomy

META FORM name="%25SYSTEMWEB%25.LogBookForm"
FORM FIELD Subject Subject Focus Study (Pt II)
FORM FIELD Status Status blank
FORM FIELD Author Author PedroDeCarvalhoPaiva
 
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