A camera system, comprising: a camera module, photographing a target object according to a focal length to generate an image; and a processor, comprising: an extending-lens-depth-of-field EDOF, module, configured to process the image according to an EDOF process to generate an EDOF image; an auto focus module, configured to adjust the focal length of the camera module according to an auto focus process; and wherein the processor is configured to classify the distance between the object and the camera system into a plurality of distance ranges and to set a plurality of predetermined focal length values respectively corresponding to the distance ranges, to select for the adjusting a target focal length based on the plurality of predetermined focal length values, to then process the image with the EDOF module according to an EDOF process to generate an EDOF image, and then to determine whether a clarity of the target object shown in the EDOF image is higher than that of a clarity threshold and when the clarity is higher than that of the clarity threshold, outputting the EDOF image; or when the clarity of the target object shown in the EDOF image is less than that of the clarity threshold, repeating the selecting step, the adjusting step, the photographing step, and the processing step, until the clarity of the target object shown in the EDOF image is higher than that of the clarity threshold. a camera module, photographing a target object according to a focal length to generate an image; and a processor, comprising: an extending-lens-depth-of-field EDOF, module, configured to process the image according to an EDOF process to generate an EDOF image; an auto focus module, configured to adjust the focal length of the camera module according to an auto focus process; and wherein the processor is configured to classify the distance between the object and the camera system into a plurality of distance ranges and to set a plurality of predetermined focal length values respectively corresponding to the distance ranges, to select for the adjusting a target focal length based on the plurality of predetermined focal length values, to then process the image with the EDOF module according to an EDOF process to generate an EDOF image, and then to determine whether a clarity of the target object shown in the EDOF image is higher than that of a clarity threshold and when the clarity is higher than that of the clarity threshold, outputting the EDOF image; or when the clarity of the target object shown in the EDOF image is less than that of the clarity threshold, repeating the selecting step, the adjusting step, the photographing step, and the processing step, until the clarity of the target object shown in the EDOF image is higher than that of the clarity threshold. an extending-lens-depth-of-field EDOF, module, configured to process the image according to an EDOF process to generate an EDOF image; an auto focus module, configured to adjust the focal length of the camera module according to an auto focus process; and wherein the processor is configured to classify the distance between the object and the camera system into a plurality of distance ranges and to set a plurality of predetermined focal length values respectively corresponding to the distance ranges, to select for the adjusting a target focal length based on the plurality of predetermined focal length values, to then process the image with the EDOF module according to an EDOF process to generate an EDOF image, and then to determine whether a clarity of the target object shown in the EDOF image is higher than that of a clarity threshold and when the clarity is higher than that of the clarity threshold, outputting the EDOF image; or when the clarity of the target object shown in the EDOF image is less than that of the clarity threshold, repeating the selecting step, the adjusting step, the photographing step, and the processing step, until the clarity of the target object shown in the EDOF image is higher than that of the clarity threshold.