Real or artefact?



Strong image processing can produce artefacts. Cameras pointed near the sun give deceiving internal lens reflections and CCD effects. Is it real?



Two hand held images show the arc. Always take several hand-held pictures of a strange phenomenon. Artefacts like lens reflections will shift and change but a real object will not.



Several different image processing routes give the same arc.



Colours are the right way around.



Geometry on the arc gives the sun position as just off the lower right hand edge. The arc is near circular except for a slight curvature difference at its indistinct top. The sun position combined with the lens focal length in the image EXIF data yields an arc radius of 43° and on the other image 41°. Theoretical radius is 42.5°. Arc width is hard to measure but is perhaps only 3.5° compared to a theory value of ~4.4°.



To be sure, we need exact reproduction of the original camera position for one of the images, exposure of a star field and subsequent calibration of the lens followed by computation of the precise sun position and then more geometry.







