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Re: Camera sextant? was: Re: On The Water Trial of Digital Camera CN
From: Marcel Tschudin
Date: 2010 Jul 5, 19:43 +0300
From: Marcel Tschudin
Date: 2010 Jul 5, 19:43 +0300
George, After some additional thoughts I do now understand that you referred here to the conversion function: > With centred optics, any radial plot, of pixel count from the centre point > of the array, Px, against offset angle A from the optical centre-line, MUST > pass through the origin, at (0,0), and MUST be antisymmetric about that > origin. When the pixel count from the centre is expressed as a function of > angle Px = f (A), then f (-A ) must equal - f (A), when we consider light > arriving with opposite offsets from the centre-line. You are right that theoretically this function has to go through the origin (0,0). However, a polynomial like a Px^3 + b Px shows only a slightly better correlation than just a linear regression with the "wrong" constant off-set. In order to get a real improvement one would have to use even higher terms. But how practical would then such function be for being tagged on the lens cover? The best fits have been obtained with the arc-tan-function. In order to obtain those parameters one has to use the Solver tool. For those who don't have this tool or are not familiar how to use it the next best option compared to the linear regression was thought to be the quadratic equation with the "wrong" constant which can be shown "automatically", i.e. without using Solver. Marcel