Laminated optical system and endoscope

A laminated optical system comprising a first lens portion having a negative refractive power, a second lens portion having a negative refractive power, a third lens portion having a positive refractive power, and a fourth lens portion having a positive refractive power which are disposed in that order from an object side to an image side,

• wherein the first lens portion has a first parallel flat plate and a first plano-concave lens having a first concave surface of which a concave surface faces the image side and a first flat surface on an outer peripheral side of the first concave surface which are disposed in that order from the object side to the image side,
• wherein a flat surface on an image side of the first parallel flat plate and a flat surface on an object side of the first plano-concave lens are adhered to each other,
• wherein the second lens portion has a second parallel flat plate and a second plano-concave lens having a second concave surface of which a concave surface faces the image side and a second flat surface on an outer peripheral side of the second concave surface which are disposed in that order from the object side to the image side,
• wherein the first flat surface of the first plano-concave lens and a flat surface on the object side of the second parallel flat plate are adhered to each other, and a flat surface on the image side of the second parallel flat plate and the second flat surface of the second plano-concave lens are adhered to each other,
• wherein the third lens portion has a first plano-convex lens having a first convex surface of which a convex surface faces the object side and a third flat surface on an outer peripheral side of the first convex surface and a third parallel flat plate which are disposed in that order from the object side to the image side,
• wherein the second concave surface of the second plano-concave lens and the first convex surface of the first plano-convex lens are disposed with an interval therebetween,
• wherein the second flat surface of the second plano-concave lens and the third flat surface of the first plano-convex lens are adhered to each other, and a flat surface on the image side of the first plano-convex lens and a flat surface on the object side of the third parallel flat plate are adhered to each other,
• wherein the fourth lens portion has a second plano-convex lens having a second convex surface of which a convex surface faces the object side and a fourth flat surface on an outer peripheral side of the second convex surface and a fourth parallel flat plate which are disposed in that order from the object side to the image side,
• wherein a flat surface on the image side of the third parallel flat plate and the second convex surface of the second plano-convex lens are disposed with an interval therebetween,
• wherein the flat surface on the image side of the third parallel flat plate and the fourth flat surface of the second plano-convex lens are adhered to each other,
• wherein a flat surface on the image side of the second plano-convex lens and a flat surface on the object side of the fourth parallel flat plate are adhered to each other,
• wherein a linear expansion coefficient of the first plano-concave lens is greater than a linear expansion coefficient of the first parallel flat plate,
• wherein a linear expansion coefficient of the second plano-concave lens is greater than a linear expansion coefficient of the second parallel flat plate,
• wherein a linear expansion coefficient of the first plano-convex lens is greater than a linear expansion coefficient of the third parallel flat plate, and
• wherein a linear expansion coefficient of the second plano-convex lens is greater than a linear expansion coefficient of the fourth parallel flat plate.