Optical system of a focus detection apparatus

1. An optical system of a focus detection apparatus, comprising:

a condenser lens positioned behind an expected focal plane of a photographing lens;

an auxiliary lens group positioned behind said condenser lens to be coaxial therewith;

a pair of separator lenses positioned behind said auxiliary lens group in close vicinity thereof and integrally molded from resin,

wherein an object image formed on said expected focal plane is divided into two images by said pair of separator lenses to be reformed on a pair of areas on a sensor, respectively, and

wherein said auxiliary lens group includes a negative lens element made of resin, and a positive lens element made of glass, and

a separator mask which is positioned between said auxiliary lens group and said pair of separator lenses and includes a pair of apertures facing said pair of separator lenses, respectively,

wherein said resin-made auxiliary lens element, said glass-made auxiliary lens element, said pair of separator lenses and said separator mask satisfy the following condition (1):

0.2< t s ·f n /( F IN ·m 0 ·q n ·P )<1.1  (1),

wherein f n designates a focal length of said resin-made auxiliary lens group;

P designates a distance between optical axes of said pair of separator lenses;

q n designates a rate of focal length change of said resin-made auxiliary lens element due to a temperature change thereof which corresponds to the sum of a variation in shape and a variation in refractive index according to a linear expansion coefficient;

t s designates a linear expansion coefficient of said pair of separator lenses due to a temperature change thereof;

F IN designates an f-number of said optical system of said focus detection apparatus that is determined by said pair of apertures of said separator lens mask; and

m 0 designates a magnification of said optical system of said focus detection apparatus.

2. The optical system according to claim 1 , further comprising a separator mask which is positioned between said auxiliary lens group and said pair of separator lenses and includes a pair of apertures facing said pair of separator lenses, respectively,

wherein said resin-made auxiliary lens element, said glass-made auxiliary lens element, said pair of separator lenses and said separator mask satisfy the following condition (1):

0.2< t s ·f n /( F IN ·m 0 ·q n ·P )<1.1  (1),

wherein f n designates a focal length of said resin-made auxiliary lens group;

P designates a distance between optical axes of said pair of separator lenses;

q n designates a rate of focal length change of said resin-made auxiliary lens element due to a temperature change thereof by 30 degrees centigrade, which corresponds to the sum of a variation in shape and a variation in refractive index according to a linear expansion coefficient;

t s designates a linear expansion coefficient of said pair of separator lenses due to a temperature change thereof by 30 degrees centigrade;

F IN designates an f-number of said optical system of said focus detection apparatus that is determined by principal rays respectively passed through said pair of apertures of said separator lens mask; and

m 0 designates a magnification of said optical system of said focus detection apparatus.

3. The optical system according to claim 1 , wherein a range of temperature change of said q n and t s is 20° C.±30° C.

4. The optical system according to claim 1 , wherein said resin-made auxiliary lens element and said glass-made auxiliary lens element satisfy the following condition (2):

−0.1<1/( m 2 ·m 3 )<4.0  (2),

wherein m 2 designates a magnification of one of said resin-made auxiliary lens element and said glass-made auxiliary lens element which is closer to said photographing lens, and

m 3 designates a magnification of the other of said resin-made auxiliary lens element and said glass-made auxiliary lens element which is closer to said image sensor.

5. An optical system of a focus detection apparatus, comprising:

a condenser lens positioned behind an expected focal plane of a photographing lens;

an auxiliary lens group positioned behind said condenser lens to be coaxial therewith; and

a pair of separator lenses positioned behind said auxiliary lens group in close vicinity thereof and integrally molded from resin,

wherein an object image formed on said expected focal plane is divided into two images by said pair of separator lenses to be reformed on a pair of areas on a sensor, respectively,

wherein said auxiliary lens group includes a negative lens element made of resin, and a positive lens element made of glass,

wherein said resin-made auxiliary lens element and said glass-made auxiliary lens element satisfy the following condition (2):

−0.1<1/( m 2 ·m 3 )<4.0  (2),

wherein m 2 designates a magnification of one of said resin-made auxiliary lens element and said glass-made auxiliary lens element which is closer to said photographing lens, and

m 3 designates a magnification of the other of said resin-made auxiliary lens element and said glass-made auxiliary lens element which is closer to said image sensor.

6. The optical system according to claim 5 , further comprising a separator mask which is positioned between said auxiliary lens group and said pair of separator lenses and includes a pair of apertures facing said pair of separator lenses, respectively,

wherein said resin-made auxiliary lens element, said glass-made auxiliary lens element, said pair of separator lenses and said separator mask satisfy the following condition (1):

0.2< t s ·f n /( F IN ·m 0 ·q n ·P )<1.1  (1),

wherein f n designates a focal length of said resin-made auxiliary lens group;

P designates a distance between optical axes of said pair of separator lenses;

q n designates a rate of focal length change of said resin-made auxiliary lens element due to a temperature change thereof by 30 degrees centigrade, which corresponds to the sum of a variation in shape and a variation in refractive index according to a linear expansion coefficient;

t s designates a linear expansion coefficient of said pair of separator lenses due to a temperature change thereof by 30 degrees centigrade;

F IN designates an f-number of said optical system of said focus detection apparatus that is determined by principal rays respectively passed through said pair of apertures of said separator tens mask; and

m 0 designates a magnification of said optical system of said focus detection apparatus.

7. The optical system according to claim 5 ,

further comprising a separator mask which is positioned between said auxiliary lens group and said pair of separator lenses and includes a pair of apertures facing said pair of separator lenses, respectively,

wherein said resin-made auxiliary lens element, said glass-made auxiliary lens element, said pair of separator lenses and said separator mask satisfy the following condition (1):

0.2< t s ·f n /( F IN ·m 0 ·q n ·P )<1.1  (1),

wherein f n designates a focal length of said resin-made auxiliary lens group;

P designates a distance between optical axes of said pair of separator lenses;

q n designates a rate of focal length change of said resin-made auxiliary lens element due to a temperature change thereof which corresponds to the sum of a variation in shape and a variation in refractive index according to a linear expansion coefficient;

t s designates a linear expansion coefficient of said pair of separator lenses due to a temperature change thereof;

F IN designates an f-number of said optical system of said focus detection apparatus that is determined by said pair of apertures of said separator lens mask; and

m 0 designates a magnification of said optical system of said focus detection apparatus,

wherein a range of temperature change of said q n and t s is 20° C.±30° C.