Optical adapter for endoscope and endoscope apparatus

1. An endoscope comprising:

a tip having distal and proximal external portions provided on an external surface of the tip; and

an adapter comprising:

a cylindrical body having an internal portion formed on an interior of the cylindrical body, the internal portion being configured to matingly engage with each of the distal and proximal external portions provided on the external surface of the tip of the endoscope, the distal and proximal external portions being separated in a longitudinal direction of the cylindrical body by a portion of the tip that does not engage the internal portion; and

wherein the cylindrical body further having an anti-slip portion formed on an exterior of the cylindrical body, the anti-slip portion having a plurality of recesses arranged circumferentially on the exterior;

the cylindrical body having a first portion with a first wall thickness, a second portion with a second wall thickness greater than the first wall thickness and a boundary between the first portion having the first wall thickness and the second portion having the second wall thickness;

the anti-slip portion is formed on the cylindrical body at the first portion having the first wall thickness; and

a position of the anti-slip portion in the longitudinal direction being set such that:

a position of the proximal external portion in the longitudinal direction does not overlap with the longitudinal position of the anti-slip portion in a state where the proximal external portion is engaged with the internal portion of the cylindrical body, and

a position of the distal external portion in the longitudinal direction is not located at the boundary, in a state where the internal portion is not engaged with the proximal external portion and the cylindrical body is prevented from falling off the tip by the distal external portion.

2. The endoscope according to claim 1 , wherein the internal portion is an internal threaded portion and the distal and proximal external portions are distal and proximal threaded portions each being configured to matingly engage with the internal threaded portion.

3. The endoscope according to claim 1 , wherein in the state where the proximal external portion is engaged with the internal portion, at least a portion of the distal external portion overlaps with the anti-slip portion in the longitudinal direction.

4. The endoscope according to claim 1 , wherein the anti-slip portion being positioned so as to overlap with at least a part of the distal external portion in the longitudinal direction in the state where the proximal external portion is engaged with the internal portion.

5. The endoscope according to claim 1 , wherein each of the plurality of recesses having a side surface having an angle of 90° or less with respect to a surface of an outer periphery of a connection ring.

6. The endoscope according to claim 1 , further comprising one or more optical elements arranged on the cylindrical body.

7. The endoscope according to claim 1 , wherein the second portion having the second wall thickness is superposed on the distal external portion in the longitudinal direction in the state where the internal portion is not engaged with the proximal external portion and the cylindrical body is prevented from falling off the tip by the distal external portion.

8. The endoscope according to claim 1 , wherein the second portion having the second wall thickness is superposed in the longitudinal direction on the proximal external portion in the state where the proximal external portion is engaged with the internal portion of the cylindrical body.