Three component lens system having external entrance and exit pupils

Claim 1

AN OPTICAL LENS SYSTEM IN WHICH BOTH THE ENTRANCE PUPIL AND THE EXIT PUPIL ARE EXTERNAL TO THE SYSTEM, COMPRISING FIRST, SECOND AND THIRD LENS COMPONENTS ARRANGED IN SEQUENCE ALONG THE OPTICAL PATH THROUGH THE LENS SYSTEM FROM OBJECT VIEWED TO IMAGE PLANE, AND SAID FIRST AND SECOND LENS COMPONENTS BEING SPACED APART BY A DISTANCE LESS THAN SAID SECOND AND THIRD LENS COMPONENTS ARE SPACED APART, THE FIRST LENS COMPONENT HAVING A POSITIVE EQUIVALENT FOCAL LENGTH, THE SECOND LENS COMPONENT HAVING A POSITIVE EQUIVALENT FOCAL LENGTH, THE THIRD LENS COMPONENT HAVING A NEGATIVE EQUIVALENT FOCAL LENGTH, THE LENS SYSTEM AS A WHOLE HAVING AN EQUIVALENT FOCAL LENGTH WHICH IS POSITIVE AND NUMERICALLY SMALLER THAN THE EQUIVALENT FOCAL LENGTH OF EACH OF THE THREE LENS COMPONENTS INDIVIDUALLY, A REAL IMAGE BEING FORMED BETWEEN THE SECOND AND THIRD LENS COMPONENTS, A VIRTUAL IMAGE OF THIS REAL IMAGE BEING FORMED BY THE THIRD LENS COMPONENT BETWEEN THE REAL IMAGE AND THE THIRD LENS COMPONENT, THE SAID FIRST, SECOND AND THIRD LENS COMPONENTS IN THEIR RELATIVE SPACINGS ARE TOGETHER SUCH THAT THE DISTANCE OF THE SAID REAL IMAGE, FORMED BETWEEN THE SECOND AND THIRD LENS COMPONENTS, FROM THE PRINCIPAL PLANE OF THE SECOND LENS COMPONENT IS LESS THAN THE DISTANCE OF SAID REAL IMAGE FROM THE PRINCIPAL PLANE OF THE THIRD LENS COMPONENT, THE SEPARATION BETWEEN THE PRINCIPAL PLANES OF THE SECOND AND THIRD LENS COMPONENTS BEING AT LEAST THREE TIMES AS GREAT AS THE SEPARATION BETWEEN THE PRINCIPAL PLANES OF THE FIRST AND SECOND LENS COMPONENTS, SAID ENTRANCE PUPIL BEING SPACED FROM SAID FIRST LENS COMPONENT BY A DISTANCE GREATER THAN ONE HALF SAID EQUIVALENT FOCAL LENGTH OF THE LENS SYSTEM.