The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light. A system with a shorter focal length bends the rays more sharply, bringing them to a focus in a …

Popes. The term pope is the name several churches give to their highest spiritual leader. In English, the term usually means the head of the Catholic Church.The most accurate information about the popes is published every year by the Holy See in the Annuario Pontificio.. Popes with the longest reigns. After Peter, who was the first Bishop of Rome and the first pope, the list of the …