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Image Scale


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#1 prsxl5



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Posted 09 April 2014 - 06:56 PM

My camera has a sensor size of 36x24mm and pixel array of 5760x3840.

Using my Meade 10inch scope with focal length 2500mm and focal ratio of f/10, how do I calculate the image scale in pixels?





#2 MistrBadgr


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Posted 10 April 2014 - 05:05 AM

Hello James,


Welcome to the forum!


Your question is a bit out of my realm and hopefully someone a little more aquainted with imaging will have a ready answer.  But, I have a question and an idea.  Are you asking about what the arc-second coverage one pixel has in the sky?  If so, one way to find out would be to take an image of a couple of stars with a known seperation.  Print the whole image out on a piece of paper.  Measure the distance between the the stars and the distance across the image.  The ratio of the distance between the stars and the distance across the picture, multiplied by the number of pixels across the picture, should give you the number of pixels between the two stars.  Divide the arc-seconds between the stars by the number of pixels you just determined, should give you the arc-second width of one pixel.


If you have trouble with any of that, let me know.  If you can take such an image and need help figuring out the actual arc-second distance between the stars, or any of the other determinations, let me know.


There may be an easier way to make the determination from the information about the scope, but I think what I told you will work using the sky.


Hope this helps,


Bill Steen

Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#3 gspie


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Posted 10 April 2014 - 03:20 PM

There is a program called CCDCALC that may answer your questions. I believe it is free, and there is a Mac version as well as Windows.
LX850 with 10" ACF OTA and Takahashi FS 60C OTA -- SBIG STT-8300M CCD with FW8G-STT Self Guiding Filter Wheel and SBIG AO-8 Adaptive Optics -- Camera Control and Image Calibration with Maxim DL/CCD Pro, Image processing with PixInsight, and final composition with Photoshop CS5


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