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Old 09-11-2012, 03:43 PM
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mithrandir (Andrew)
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mithrandir is offline
Join Date: Jan 2009
Location: Glenhaven
Posts: 4,161
Graham, your best bet is to take an image and plate solve it with something like which does not need an estimate of focal length, or UniMap for which a ball park figure will get it started.

That should either directly give you the arcsec/pixel or the FOV from which you can derive the ASP since you know the pixel size.

Then the true focal length is given by:

focal_length = 206.265 * pixel_size / arcsec_per_pixel

focal_length in mm
pixel_size in um
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