Objective optical system, method of manufacturing objective optical system image pickup apparatus, and endoscope
The objective optical system includes a flat plate disposed closest to an object side and a plano-concave negative lens having a flat surface facing the object side. The flat plate is a transparent material harder than the plano-concave lens. The flat plate and the plano-concave lens having an equal diameter are bonded. The following Conditional Expressions (1) and (7) are satisfied: 10≤φ1/ t 1≤70 (1) 7≤φ1/( t 1+ t 2)≤9.71 (7) where φ1 is an outer diameter of the flat plate, t1 is a thickness of the flat plate, and t2 is a thickness of the plano-concave negative lens along an optical axis.
1. An objective optical system comprising:
a flat plate disposed closest to an object side; and
a plano-concave negative lens having a flat surface facing the object side,
wherein:
the flat plate is made of a transparent material harder than a material of which the plano-concave lens is made,
the flat plate and the plano-concave lens have equal diameters and are bonded, and
the following Conditional Expressions (1), (3), and (7) are satisfied:
10≤φ1 /t 1≤70 (1)
0.4≤( t 1/ t 2)×( e 1/ e 2)≤5 (3)
7≤φ1/( t 1+ t 2)≤9.71 (7)
where:
φ1 is an outer diameter of the flat plate,
t1 is a thickness of the flat plate,
t2 is a thickness of the plano-concave negative lens along an optical axis,
e1 is an elastic modulus of the flat plate, and
e2 is an elastic modulus of the plano-concave negative lens.
2. The objective optical system according to claim 1 , wherein the flat plate and the plano-concave negative lens are bonded by activated bonding.
3. The objective optical system according to claim 1 , wherein the following Conditional Expression (2) is satisfied:
0.1≤ t 1/ t 2≤1.4 (2).
4. The objective optical system according to claim 1 , wherein the following Conditional Expression (4) is satisfied:
| v 1− v 2|/Max( v 1, v 2)≤0.2 (4)
where:
v1 is a coefficient of linear expansion of the flat plate,
v2 is a coefficient of linear expansion of the plano-concave negative lens, and
Max(v1,v2) is a larger value of v1 and v2.
5. The objective optical system according to claim 1 , wherein the following Conditional Expression (5) is satisfied:
120°≤ω (5)
where ω is an angle of view of the objective optical system.
6. The objective optical system according to claim 1 , wherein the following Conditional Expression (6) is satisfied:
1.8 ≤n 2≤2.2 (6)
where n2 is a refractive index of the plano-concave negative lens for d-line.
7. The objective optical system according to claim 1 , wherein the following Conditional Expression (1′) is satisfied:
12≤φ1/ t 1≤50 (1′).
8. The objective optical system according to claim 1 , wherein the following Conditional Expression (1″) is satisfied:
14≤φ1/ t 1≤34 (1″).
9. The objective optical system according to claim 1 , wherein the following Conditional Expression (2′) is satisfied:
0.2 ≤t 1 /t 2≤1.2 (2′).
10. The objective optical system according to claim 1 , wherein the following Conditional Expression (2″) is satisfied:
0.4≤ t 1/ t 2≤1.0 (2″).
11. The objective optical system according to claim 1 , wherein the flat plate is made of a transparent material with a Vickers hardness of 14 GPa or higher.
12. The objective optical system according to claim 1 , wherein the flat plate is made of sapphire glass or transparent ceramics.
13. An image pickup apparatus comprising:
an objective optical system; and
an imager,
wherein the objective optical system is the objective optical system according to claim 1 .
14. An endoscope comprising:
an objective optical system; and
an imager,
wherein the objective optical system is the objective optical system according to claim 1 .
15. A method of manufacturing an objective optical system, the method comprising:
providing a first substrate made of a transparent material;
providing a second substrate made of an optical glass to form a plano-concave negative lens;
activating and bonding the first substrate and the second substrate;
making the activated and bonded first substrate and second substrate into thin pieces, the first substrate and the second substrate each having dimensions corresponding to a plurality of the plano-concave negative lenses; and
performing lens processing on the second substrate after the step of making the thin pieces,
wherein:
the first substrate is made of a material harder than a material of which the second substrate is made,
the first substrate is made of sapphire glass,
a plane perpendicular to a C-axis of monocrystalline sapphire glass in the first substrate is activated and bonded to the second substrate, and
the following Conditional Expressions (1) and (7) are satisfied:
10≤φ1/ t 1≤70 (1)
7≤φ1/( t 1+ t 2)≤9.71 (7)
where:
φ1 is an outer diameter of the first substrate,
t1 is a thickness of the first substrate, and
t2 is a thickness of the second substrate along an optical axis.
16. The method according to claim 15 , wherein the step of activating and bonding includes a surface activated bonding step or a plasma activated bonding step.