Focus adjusting device for zoom lens assembly

A focus adjusting device for flange back adjustment of an inner focus lens assembly including a zoom lens, a focus lens, and a compensator lens, comprising:

• zoom lens driving means for driving said zoom lens;
• zoom lens position detecting means for detecting information on position of said zoom lens;
• focus lens driving means for driving said focus lens;
• focal condition detecting means for detecting a focal condition;
• and
• computing means, responsive to said zoom lens position detecting means and said focal condition detecting means and operatively connected with said zoom lens driving means and said focus lens driving means, for selectively moving said zoom lens and said focus lens in a predetermined sequence including:
• moving the zoom lens to a mechanical end position (ZMW) on a wide side,
• moving the focus lens to a position (FCS0) wherein focus is achieved with the zoom lens at said wide side mechanical end,
• moving the focus lens by a predetermined amount (FCS) toward a telephoto end,
• moving the zoom lens to a position (ZOT) wherein focus is achieved, and
• moving the zoom lens to a mechanical end position (ZMT) at the telephoto end;
• and
• deriving the difference (ZMT-ZMW) between the wide side mechanical end position of the zoom lens and the telephoto side mechanical end position of the zoom lens using an output from said zoom lens position detecting means;
• using (a) a predetermined ratio of:
• (i) the difference between a designed wide side mechanical end of the zoom lens and a designed telephoto side mechanical end of the zoom lens, to (ii) the difference between a designed wide side optical end of the zoom lens and a designed telephoto optical end of the zoom lens, (b) the difference (ZMT-ZMW) between the determined wide side mechanical end of the zoom lens and the determined telephoto side mechanical end of the zoom lens, and (c) the determined (ZOT) position, to derive a wide side optical end (ZOW) position for the zoom lens;
• determining if the difference between the derived wide side optical end position (ZOW) and the (FSCO) position, falls within a predetermined range;
• and
• recording the (ZOW) and (ZOT) values if the difference between (ZOW) and (FSCO) falls within the predetermined range.