NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Which diameter of the sun in digital photos ?
From: Greg Rudzinski
Date: 2009 Aug 21, 11:26 -0700
From: Greg Rudzinski
Date: 2009 Aug 21, 11:26 -0700
Marcel, I agree with George's comments and would like to add that my Canon DSLR Rebel camera produces reliable images when way under exposed in black and white. Try using no filtering with settings of f22, 1/4000, ISO 100 and then increase the amount of light incrementally until the horizon is just visible as a reference. Also try a pair of opposing circular polarizers held out in front of the camera lens and adjusted to produce a faint image of the sun with a bright horizon beneath it. Experiment to find the best combinations for your particular camera and lenses. Greg On Aug 21, 4:49�am, Marcel Tschudinwrote: > For investigating the refraction near the horizon I perform systematic > observations by photographing sunsets. So far I used the horizontal > diameter of the sun as a reference scale (pixel per degree) for > measuring the sun's position above the apparent horizon. > > Recently I compared this scale to one derived from pictures of > landscapes and found to my surprise that they differ by around 8%; the > sun is systematically slightly larger. > > The scale in landscape photos has been measured with distinct features > and the distances measured with Google Earth. The scale for (not > overexposed) sun photos has been calculated with the angular size of > the sun for the corresponding days; this size is based on the sun's > diameter (of the photosphere) and the earth's distance. > > The difference is not related to refraction since the measurements are > made in horizontal direction. �Any idea, why those two scales differ? > It is known that some CCDs have a leak in the IR, also the one in my > camera. Could this be responsible for it? Does anyone know more on > this? > > Marcel --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---