US 9,810,878 B2
Inner focus lens system and image pickup apparatus using the same
Masaru Morooka, Tokyo (JP)
Assigned to OLYMPUS CORPORATION, Tokyo (JP)
Filed by Olympus Corporation
Filed on Dec. 19, 2014, as Appl. No. 14/576,908.
Application 14/576,908 is a division of application No. 13/707,758, filed on Dec. 7, 2012, granted, now 8,947,793.
Claims priority of application No. 2011-279434 (JP), filed on Dec. 21, 2011.
Prior Publication US 2015/0103230 A1, Apr. 16, 2015
Int. Cl. G02B 15/14 (2006.01); G02B 9/64 (2006.01); G02B 15/22 (2006.01); G02B 9/34 (2006.01); G02B 15/177 (2006.01)
CPC G02B 9/64 (2013.01) [G02B 9/34 (2013.01); G02B 15/14 (2013.01); G02B 15/177 (2013.01); G02B 15/22 (2013.01)] 21 Claims
OG exemplary drawing
 
1. An inner focus lens system comprising, in order from an object side to an image side,
a first lens unit,
an aperture stop,
a second lens unit having a positive refractive power,
a third lens unit having a negative refractive power, and
a fourth lens unit having a positive refractive power, wherein
a total number of lens units in the inner focus lens system is four, which is the first lens unit, the second lens unit, the third lens unit, and the fourth lens unit,
the first lens unit has at least one negative lens and at least one positive lens,
the second lens unit has at least one negative lens and at least one positive lens,
the third lens unit consists of one negative lens,
the fourth lens unit has at least one negative lens and at least one positive lens,
at a time of focusing on an object at a short distance from an object at infinity, the third lens unit moves to the image side so as to lengthen a distance to the second lens unit and to shorten a distance to the fourth lens unit,
an F number of the inner focus lens system is 2 or less, and
an exit surface of the first lens unit and an incidence surface of the second lens unit are concave toward the aperture stop.