Distal end optical unit for electronic endoscope
A distal end optical unit for an electronic endoscope includes a first supporting tube configured to support an image sensor therein, a second supporting tube, and a third supporting tube configured to support an objective optical system. The first supporting tube includes a first open end, a first sealed end that is hermetically sealed, and a metal-covered inner circumferential surface. The second supporting tube includes a second open end, a second sealed end that is hermetically sealed with a cover lens, and a metal-covered outer circumferential surface. The third supporting tube has an inner circumferential surface with a low reflectivity. The third supporting tube is fitted into the second supporting tube. The second open end of the second supporting tube is fitted into and hermetically joined to the first open end of the first supporting tube.
1. A distal end optical unit for an electronic endo scope, comprising:
a first supporting tube configured to support an image sensor therein;
a second supporting tube; and
a third supporting tube configured to support an objective optical system,
wherein the first supporting tube includes:
a first open end provided at a distal end thereof;
a first sealed end provided at a proximal end thereof that is hermetically sealed; and
a metal-covered inner circumferential surface,
wherein the second supporting tube includes:
a second open end provided at a proximal end thereof;
a second sealed end provided at a distal end thereof that is hermetically sealed with a cover lens; and
a metal-covered outer circumferential surface,
wherein the image sensor is entirely housed inside the first supporting tube in an axial direction of the first supporting tube,
wherein the third supporting tube has an inner circumferential surface with a low reflectivity, the third supporting tube being fitted into the second supporting tube,
wherein the second open end provided at the proximal end of the second supporting tube is fitted into and hermetically joined to the first open end provided at the distal end of the first supporting tube,
wherein the second supporting tube is fitted into the first supporting tube and fitted around the third supporting tube such that the third supporting tube is entirely housed inside the second supporting tube in an axial direction of the second supporting tube, and
wherein the second supporting tube includes a first portion at a side of the second open end, in which the third supporting tube is not fitted, and a second portion in which the third supporting tube is fitted, the first portion having an inner diameter larger than that of the second portion.
2. The distal end optical unit according to claim 1 , wherein the metal-covered inner circumferential surface of the first supporting tube includes a gold surface layer.
3. The distal end optical unit according to claim 1 , wherein the first supporting tube is metal-plated over an entire surface thereof.
4. The distal end optical unit according to claim 3 , wherein the first supporting tube is double-plated with a gold-plated surface layer on a nickel-plated foundation layer over the entire surface thereof.
5. The distal end optical unit according to claim 1 , wherein the first sealed end is hermetically sealed with the image sensor joined to the metal-covered inner circumferential surface of the first supporting tube by one of soldering and brazing.
6. The distal end optical unit according to claim 1 , wherein the metal-covered outer circumferential surface of the second supporting tube includes a gold surface layer.
7. The distal end optical unit according to claim 1 , wherein the second supporting tube is metal-plated over an entire surface thereof.
8. The distal end optical unit according to claim 7 , wherein the second supporting tube is double-plated with a gold-plated surface layer on a nickel-plated foundation layer over the entire surface thereof.
9. The distal end optical unit according to claim 1 , wherein the cover lens has a metalized surface,
wherein the second sealed end of the second supporting tube is hermetically sealed with the metalized surface of the cover lens being joined thereto with a tin alloy.
10. The distal end optical unit according to claim 1 , wherein the first portion of the second supporting tube has an inner circumferential surface covered with black coating material.
11. The distal end optical unit according to claim 1 , wherein the second supporting tube is formed from material with a thermal expansion coefficient as low as that of the cover lens.
12. The distal end optical unit according to claim 11 , wherein the second supporting tube is formed from iron-nickel-cobalt alloy.
13. The distal end optical unit according to claim 1 , wherein the inner circumferential surface of the third supporting tube is covered with black material.
14. The distal end optical unit according to claim 13 , wherein the third supporting tube is covered with the black material over an entire surface thereof.
15. The distal end optical unit according to claim 14 , wherein the third supporting tube is formed from metal material and plated with chrome oxide over the entire surface thereof.
16. The distal end optical unit according to claim 1 , wherein the second open end of the second supporting tube is fitted into and hermetically joined to the first open end of the first supporting tube by one of soldering and brazing.