Automatic ranging and automatic focusing

The method of automatically focusing a camera system to an object, said camera system having an aperture through which light enters, a light filter, an image detector, fan image processor operatively connected to said image detector, an optical system having a first principal plane and a second principal plane, said second principal plane being arranged closer to said image detector than said first principal plane, said camera system characterizable by a Modulation Transfer Function (MTF) at a set of object distances and a set of discrete frequencies, said MTF determinable by a set of camera parameters and a distance of said object, said set of camera parameters comprising at least one of (i) distance (s) between said second principal plane and said image detector, (ii) diameter (D) of said camera aperture, (iii) focal length (f) of said optical system, and (iv) spectral characteristic .lambda. of said light filter, said camera system configurable to at least a first camera setting and a second camera setting the first camera setting corresponding to a first set of camera parameters and the second camera setting corresponding to a second set of camera parameters, the second set of camera parameters having at least one camera parameter value which is different from the values of said first set of camera parameters, said method comprising:

• a) calculating a ratio table at said set of object distances and said set of discrete frequencies by specifying the ratio of said MTF at said first camera setting to said MTF at said second camera setting;
• b) transforming said ratio table through a log-by-rho-squared transformation to obtain a stored table;
• c) setting said camera to said first set of camera parameters;
• d) forming a first image of said object with said optical system on said image detector, and recording said first image in said image processor as a first digital image, said first digital image being a two dimensional signal;
• e) summing said first digital image along a particular direction to obtain a first signal, said first signal being a one-dimensional signal, whereby the effect of noise is significantly reduced and subsequent computations are significantly reduced;
• f0 normalizing said first signal with respect to its mean value to provide a first normalized signal;
• g) calculating a first set of Fourier coefficients of said first normalized signal at said set of discrete frequencies;
• h) setting said camera system to said second set of camera parameters;
• i) forming a second image of said object with said optical system on said image detector, and recording said second image in said image processor as a second digital image, said second digital image being a two-dimensional signal;
• j) summing said second digital image along said particular direction to obtain a second signal, said second signal being a one-dimensional signal, whereby the effect of noise is significantly reduced and subsequent computations are significantly reduced;
• k) normalizing said second signal with respect to its mean value to provide a second normalized signal;
• l) calculating a second set of Fourier coefficients of said second normalize signal at said set of discrete frequencies;
• m) dividing said first set of Fourier coefficients by said second set of Fourier coefficients to provide a set of ratio values;
• n) transforming said set of ratio values through log-by-rho-squared transformation to obtain a calculated table;
• o) calculating a set of focus camera parameters corresponding to camera settings on the basis of said calculated table and said stored table;
• and
• p) adjusting the configuration of said camera system to the camera settings specified by said set of focus camera parameters, whereby automatic focusing is accomplished.