Nice image Mario
You can work out the f ratio by first working out the focal length with the following formula.
"The solution is to work backwards from a captured image and calculate the focal length directly. All you need to know the pixel size of your camera (in microns) and then use the following formula:
F = 206.265 x P x U
---------------
O
P is the size of the object in pixels as captured
U is the pixel size of the camera in microns
O is the true size of the object in arc-seconds
F will be the focal length as calculated from this formula, in mm"
Then simply divide by the aperture in mm (eg 200) to derive an f ratio. Jupiter was 49.4" (arc-seconds) Diameter on that night according to winJUPOS. You must of course use an image that has not been resized by resampling to retain the original number of camera pixels covered by the planet.
Hope that helps
