The invention concerns a method and system for selective control of charging a power source. The modem process converts, digital information into transmit data samples. Testing the squalene content in the final lots is easier than investigating the characteristics of the filter, and so a squalene assay simplifies the quality control of oil-in-water emulsions. When the first focal detector is used for focal adjustment, a detection of the focal state is performed on the basis of only the information obtained by the relative position detector.