an objective lens adapter according to an embodiment of the present invention will be described below referring to fig1 to 5 . as shown in fig2 , an objective lens adapter 1 according to this embodiment , which is an objective lens adapter 1 that is attachably / detachably attached to an objective lens 3 for in vivo observation and that has a small - diameter distal - end portion 2 , is provided with a fixed member 5 that is fixed to a lens tube 4 of the objective lens 3 , a distal - end member 6 that is disposed so as to cover the small - diameter distal - end portion 2 of the objective lens 3 , and a compression coil spring ( elastic member ) 7 that is disposed between the distal - end member 6 and the fixed member 5 . the fixed member 5 is formed substantially cylindrically , has an inside diameter that allows it to fit on the lens tube 4 of the objective lens 3 , and has an inner - rib like inner flange portion 5 a on one end extending radially inward . the inner flange portion 5 a is provided with a through - hole 5 b that penetrates in the axial direction . the fixed member 5 can be fixed onto the lens tube 4 of the objective lens 3 by friction from pressing the distal end of a set screw 8 , which is screwed into a threaded hole 5 c penetrating in the radial direction thereof , against the external surface of the lens tube 4 of the objective lens 3 . the distal - end member 6 is provided with a substantially cylindrical tubular portion 6 a , a prism ( optical element ) 9 fixed on one end of the tubular portion 6 a , and an outer - rib like outer flange portion 6 b that extends radially outward on the other end of the tubular portion 6 a . the tubular portion 6 a has an outside diameter slightly smaller than the inside diameter of the through - hole 5 b of the inner flange portion 5 a . in addition , the outer flange portion 6 b has an outside diameter sufficiently larger than the inside diameter of the through hole 5 b . reference sign 6 d in the drawings is a stopper that sets the position of the distal - end member 6 to a predetermined position with respect to the fixed member 5 . the tubular portion 6 a has a sharp portion 6 c whose distal end is in a cut - off configuration at a 45 ° angle with respect to the axis line . the prism 9 is formed in a columnar shape as shown in fig3 and has a reflection surface 9 a inclined at 45 ° with respect to the axis line . the prism 9 is fittingly accommodated in the sharp portion 6 c at the distal end of the tubular portion 6 a . as shown in fig3 and 4 , a ring shaped spacer 10 whose thickness is controlled is disposed on the surface of the prism 9 inside the tubular portion 6 a . by inserting the spacer 10 , direct contact between the prism 9 and a lens ( not shown ) at the distal end of the objective lens 3 is avoided , thereby preventing damage to the prism 9 and the lens at the distal end of the objective lens 3 . in addition , as shown in fig4 and 5 , a part of the side wall of the tubular portion 6 a is cut away on the side of the sharp portion 6 c , exposing the prism 9 accommodated inside . in addition , so as not to form a large level difference between the surface of the prism 9 exposed to the outside and the tubular portion 6 a , the side wall of the tubular portion 6 a is also cut away in an area continuous with the prism 9 and is sealed by bonding a plate portion 11 whose plate thickness gradually increases . the reflection surface 9 a is covered by a cover member 12 , and , as shown in fig1 to 3 , the surface of the cover member 12 opposing the reflection surface 9 a is provided with a concave portion 12 a close to the center position thereof . by disposing the concave portion 12 a opposite the reflection surface 9 a of the prism 9 , an air layer can be formed on the back surface side of the reflection surface 9 a , and thus total reflection of light at the reflection surface 9 a is possible . by having the tubular portion 6 a penetrate the through - hole 5 b , the compression coil spring 7 is disposed in a position sandwiched in the axial direction between the outer flange portion 6 b disposed inside the fixed member 5 and the inner flange portion 5 a of the fixed member 5 . thus , by relatively moving the fixed member 5 and the distal - end member 6 in the axial direction , the amount of elastic deformation of the compression coil spring 7 is changed , causing mutual elastic forces to act . the operation of the thus - configured objective lens adapter 1 according to this embodiment will be described below . to attach the objective lens adapter 1 according to this embodiment to the distal end of the objective lens 3 having the small - diameter distal - end portion 2 , the fixed member 5 and the distal - end member 6 of the objective lens adapter 1 are placed thereon from the small - diameter distal - end portion 2 side of the objective lens 3 to bring the prism 9 into contact with the distal - end surface of the small - diameter distal - end portion 2 via the spacer 10 . from this state , the fixed member 5 is moved with respect to the distal - end member 6 , in a direction indicated by an arrow a in fig2 , toward the proximal end of the objective lens 3 ; thereby the compression coil spring 7 sandwiched between the outer flange portion 6 b of the distal - end member 6 and the inner flange portion 5 a of the fixed member 5 is compressed , generating an elastic force . then , the set screw 8 provided on the fixed member 5 is screwed into the threaded hole 5 c in a state wherein the compression coil spring 7 is elastically deformed enough to obtain a predetermined elastic force ; the fixed member 5 can be fixed in that position by pressing the distal end of the set screw 8 against the external surface of the lens tube 4 of the objective lens 3 . by doing so , the prism 9 can be precisely positioned with respect to the objective lens 3 because the state in which the prism 9 is pressed onto the distal end of the small - diameter distal - end portion 2 via the spacer 10 is maintained by means of the elastic force of the compression coil spring 7 . in addition , generation of an excessive pressing force is prevented because the pressing is achieved by means of the elastic force of the compression coil spring 7 , and thus occurrence of the problem of the small - diameter distal - end portion 2 of the objective lens 3 and the prism 9 being damaged can be proactively prevented . in particular , in the case of the objective lens 3 for observing the internal condition of brain tissue , the small - diameter distal - end portion 2 is extremely thin , and therefore , attachment / detachment by screws tends to apply an excessive pressing force ; however , an advantage of this embodiment is that there is no such problem . with the objective lens adapter 1 according to this embodiment , attached to the distal end of the objective lens 3 in this way , it is possible to simplify the procedure of piercing biological tissue with the sharp portion 6 c provided on the distal end . in other words , whereas a part of the biological tissue is crushed when piercing with the small - diameter distal - end portion 2 of an objective lens 3 with a flat distal end as it is , causing severe damage , according to this embodiment , there is an advantage in that , due to the sharp portion 6 c , the objective lens 3 can pierce the biological tissue without inflicting damage . in addition , because the side wall adjacent to the sharp portion 6 c is cut away to expose a part of the prism 9 , when piercing the biological tissue , the biological tissue can be brought into contact with the exposed surface of the prism 9 . furthermore , because the objective lens adapter 1 is configured so as not to form a level difference between the surface of the prism 9 and the external surface of the tubular portion 6 a , when piercing the biological tissue , the problem of the biological tissue being scraped by the level difference thereby inflicting damage can be prevented . then , the illumination light guided from the objective lens 3 side is emitted from the small - diameter distal - end portion 2 , is incident on the prism 9 , is deflected 90 ° at the reflection surface 9 a of the prism 9 , and thus the illumination light is radiated onto the biological tissue in contact with the surface of the prism 9 from a notch 6 e provided in the tubular portion 6 a . in the case where the illumination light is excitation light , the illumination light excites a fluorescent substance that exists in the biological tissue , generating fluorescence , and the generated fluorescence returns along the same path to be collected by the objective lens 3 . in this case , because the cover member 12 , disposed so as to cover the reflection surface 9 a of the prism 9 , has the concave portion 12 a that forms the air layer with the prism 9 , it is possible to bring about total reflection of light at the reflection surface 9 a . as a result , reduction of the intensity of the illumination light radiated onto the biological tissue and the detected light , such as fluorescence obtained from the biological tissue , is prevented ; the illumination efficiency and the detection efficiency are improved ; and it is thus possible to conduct observation with a bright image . in addition , with the objective lens adapter 1 according to this embodiment , when conducting multiple observations of the same site with time intervals therebetween , after conducting an observation with the objective lens 3 , having the objective lens adapter 1 attached thereto , piercing biological tissue , the set screw 8 is loosened to release the fixing of the fixed member 5 to the lens tube 4 of the objective lens 3 , thereby making it possible to withdraw the objective lens 3 from the objective lens adapter 1 while leaving the objective lens adapter 1 piercing the biological tissue . then , to resume observation , the objective lens 3 may be inserted into and fixed to the objective lens adapter 1 that pierces the biological tissue . note that , in this embodiment , the sharp portion 6 c , which is shaped as if the distal end of the tubular portion 6 a is cut off at an angle , is provided , and the prism 9 , having the reflection surface 9 a inclined at 45 °, is disposed inside ; however , instead , a prism 9 having a reflection surface 9 a inclined at an angle other than 45 ° may be adopted . although the cover member 12 having the concave portion 12 a opposing the reflection surface 9 a of the prism 9 is provided , instead , a metallic thin film , a dielectric multilayer film , etc ., may be formed on the reflection surface 9 a . in this case , the reflection efficiency becomes lower than in the case of total reflection , but it is advantageous in that the cover member 12 and the concave portion 12 a are not necessary . in addition , although the prism 9 having the reflection surface 9 a is adopted as an optical element in this embodiment , instead , a glass flat plate member that transmits light in the optical axis direction may be adopted . by doing so , the working distance can be adjusted to the optimal position . in addition , although the columnar prism 9 is accommodated in the cylindrical tubular portion 6 a , instead , a triangular prism ( not shown ) may be employed , and an accommodation portion may be formed at the distal end of the tubular portion 6 a in such a shape that the triangular prism can be accommodated therein . further , when using the triangular prism , as shown in fig6 , the plate member 11 may be omitted by providing a thick - walled tubular portion 6 a . additionally , as shown in fig7 , the plate member 11 may be omitted while keeping the outside diameter small by decentering the inside diameter and outside diameter of the tubular portion thereby forming a thick - walled portion .
high - precision observation is made possible while allowing contact between a distal end of an objective lens and an optical element without damaging the distal end of the objective lens and the optical element even when attaching to and detaching from the distal end of the objective lens . provided is an objective lens adapter including a fixed member that is fixed to a lens tube of an objective lens , a distal - end member including an optical element that is made to be placed in contact with the distal - end surface of the objective lens , and an elastic member that is disposed between the distal - end member and the fixed member and that urges the optical element in a direction that causes the optical element to contact the distal - end surface of the objective lens .