The present invention relates to an endoscope apparatus and, more particularly, to a device for adjusting a light quantity of an illuminating light for an endoscope depending upon used manners of the endoscope.
FIG. 1 shows a conventional endoscope apparatus which comrpises a usual endoscope 10 and a light source unit 20 for supplying an illuminating light to the endoscope 10. The endoscope 10 comprises an operating portion 11, an inserting portion 12 extending from the operating portion 11, a light guide cable 13 extending from the operating portion 11, and an ocular portion 14 provided at an end of the operating portion 11. The inserting portion 12 is flexible and is adapted to be inserted into a body cavity. The inserting portion 12 is comprised of a bendable section 12a adjacent a distal end of the inserting portion 12, and a hard or rigid tip component 12b at an end of the bendable section 12a adjacent the distal end of the inserting portion 12. The bendable section 12a has a curvature thereof which is controlled through a cable extending through the inserting portion 12 by a remote-control at the operating portion 11. The light guide cable 13 is provided at a distal end thereof with a plug 13a. The tip component 12b is provided in an end face thereof with a viewing window 12c and an illuminating window 12d. An optical fiber bundle 16 has one end 16a thereof which is optically connected to the viewing window 12c through an objective optical system 15. The optical fiber bundle 16 extends through the inserting portion 12 and the operating portion 11 and has the other end 16b optically connected to an ocular optical system 17 of the ocular portion 14. An optical transmission system, i.e., optical fiber bundle 18 has one end 18a thereof which is optically connected to the illuminating window 12d. The optical fiber bundle 18 extends through the inserting portion 12, the operating portion 11 and the light guide cable 13 and has the other end 18b which reaches a tip end of the plug 13a.
The light source unit 20 comprises a concave mirror 21 and a lamp 22 disposed at a center of the concave mirror 21.
A light from the lamp 22 is reflected from the concave mirror 21, and the reflected light is supplied to the other end 18b of the optical fiber bundle 18 while a luminous flux of the reflected light is gradually restricted. The light supplied to the other end 18b of the optical fiber bundle 18 passes through the bundle 18 and is irradiated into the body cavity from the illuminating window 12d. Thus, an interior of the body cavity is illuminated. An image of the illuminated interior of the body cavity is viewed through the viewing window 12c, objective optical system 15, optical fiber bundle 16 and ocular optical system 17.
When the inserting portion 12 of the endoscope 10 is inserted into the body cavity such as, for example, an alimentary canal, a brightness of an image obtained at the ocular portion 14 varies depending upon conditions under which the endoscope 10 is disposed or positioned. For example, as shown in FIG. 3, when the endoscope 10 is disposed such that a field of view thereof is directed substantially longitudinally of the alimentary canal T, a proportion or rate of a light quantity of the light reflected and returned to the viewing window 12c of the inserting portion 12, with respect to the illuminating light having a constant light quantity is low, because a distance from the viewing window 12c to a wall surface of the alimentary canal T is long and an angle of the illuminating light with respect to the wall surface is small. By contrast, when, as shown in FIG. 4, the endoscope 10 views the alimentary canal T in such a manner that the illuminating window 12d and the viewing window 12c of the inserting portion 12 face to the wall surface of the alimentary canal T, and when, as shown in FIG. 5, the endoscope 10 views a convex morbid part such as a polyp P, a proportion of a light quantity of the light reflected and returned to the viewing window 12c, with respect to the illuminating light having a constant light quantity is high, because a distance from the illuminating window 12d to the wall surface of the alimentary canal T or the surface of the polyp P is short and an angle of the illuminating light with respect to such surface is great, in particular, the light in a central region of a luminous flux of the illuminating light from the illuminating window 12d is applied to such surface substantially perpendicularly. Accordingly, when the illuminating light is utilized which has a constant light quantity, the brightness of the image obtained at the ocular portion 14 varies as a whole depending upon the used manners of the endoscope 10.
It is necessary for the image at the ocular portion 14 to have an adequate or suitable brightness. The image which is too bright or dark would hinder photographing and observation of the image. For this purpose, a light quantity adjusting device is disposed in position indicated by the dot-and-dash line X in FIG. 1 between the light source unit 10 and the tip end of the plug 13a, i.e., the other end 18b of the optical fiber bundle 18, for adjusting the light quantity of the illuminating light supplied from the light source unit 20 to the other end 18b of the optical fiber bundle 18.
As shown in FIGS. 6 and 7, a conventional light quantity adjusting device 100 as is disclosed in Japanese Patent Publication No. 47-44644 and Japanese Utility Model Publication No. 51-16286, comprises a pair of elongated shield members 101 and 101 which have their respective upper ends mounted on a common pivot shaft 105 for angularly movement therearound. Recutangular shield elements 102 and 102 are integrally connected to lower ends of the respective shield members 101 and 101, respectively, and cooperate with each other to variably shield, the luminous flux A of the illuminating light from the light source unit 20.
When the endoscope 10 is utilized under the condition shown in FIG. 3, the shield elements 102 and 102 are moved away from each other to enlarge a space therebetween, i.e., to fully open the luminous flux A, for example, to thereby increase the light quantity of the illuminating light supplied to the other end 18b of the optical fiber bundle 18. When the endoscope 10 is utilized under the conditions shown in FIGS. 4 and 5, the shield elements 102 and 102 are moved toward each other to reduce the space therebetween so as to bring the shield elements 102 and 102 to a restricted condition shown in FIG. 6, for example, to thereby decrease the light quantity of the illuminating light. In this manner, the brightness of the image at the ocular portion 14 is adjusted.
In considering the above-described prior art and the present invention to be described later, it will be important to understand the transmission principle of illuminating light as shown in FIG. 2. Specifically, the light having an incidence angle .theta. supplied to the other end 18b of the optical fiber bundle 18 from the lamp 22 passes through the optical fiber bundle 18 and is irradiated into the body cavity from the one end 18a of the bundle 18 through the illuminating window 12d, but the irradiated light is in the form of a cone having a solid angle 2.theta.. Accordingly, as shown in FIG. 6 and 7, assuming that the luminous flux A is imaginarily divided in cross-section at the position X in FIG. 1 into a central region Ac including an optical axis 0 of the luminous flux A and the vicinity thereof and having a small incidence angle .theta., and a peripheral region Ar surrounding the central region Ac and having a large incidence angle .theta., when a portion of the peripheral region Ar is shielded by means of the above-described shield elements 102 and 102, the light quantity of a peripheral region of the illuminating light irradiated into the body cavity is decreased, but the light quantity of a central region of the illuminating light is not decreased. Conversely, when a portion of the central region Ac is shielded, the light quantity of only the central region of the illuminating light irradiated into the body cavity is decreased.
In addition, it is normal or usual that the central region of the illuminating light is higher in light quantity than the peripheral region thereof, because of the light diffusion characteristic of the optical fiber bundle.
It is possible for the above-described conventional light quantity adjusting device 100 to adjust the entire brightness of the image obtained at the ocular portion 14. However, no sufficient consideration has been made to a distribution of the brightness of the image. Hereunder, detailed description will be made to each of the used manners of the endoscope.
When the endoscope is disposed under the condition shown in FIG. 3, a deep portion of the alimentary canal T is imaged on a central region of the image obtained at the ocular portion 14, and the wall surface of the canal T adjacent the distal end of the inserting portion 12 is imaged on a peripheral region of the image. The wall surface adjacent the distal end of the inserting portion 12 is closer to the illuminating window 12d than the deep portion and, therefore, a proportion or rate of the light quantity returned from the wall surface to the viewing window 12c with respect to the constant light quantity irradiated from the illuminating window 12c is high. Accordingly, if the light is uniformly distributed, the peripheral region of the image would be too bright, and the central region of the image would be too dark. In practice, however, since the central region is higher in light quantity than the peripheral region due to the light diffusion characeristic of the optical fiber bundle, the brightness of the image obtained at the ocular portion 14 is uniformized as a whole, and substantially no problem would occur.
When the endoscope is disposed under the condition shown in FIG. 4 or 5, a major portion of the irradiated light in the central region of the field of view is reflected and returned to the viewing window 12c, because the distance from the viewing window to the wall surface or the polyp P is short and the angle of the irradiated light is approximately right angles. In the peripheral region of the field of view, however, only a portion of the irradiated light is returned to the viewing window 12c, because the distance from the illuminating window 12b to the wall surface is long and the angle of irradiated light is small as compared with that in the central region so that a major portion of the irradiated light is reflected as shown by the broken lines. For these reasons, in combination with the light diffusion characteristic of the optical fiber bundle 18, the central region of the image obtained at the ocular portion 14 becomes too bright as compared with the peripheral region of the image. In view of this, if the above-described adjusting device 100 is restricted as shown, for example, in FIG. 6, the central region Ac of the luminous flux A is not entirely shield, but only a portion of the peripheral region Ar is shield. Accordingly, although the entire light quantity supplied to the other end 18b of the optical fiber bundle 18 is reduced, the brightness of the central region of the image obtained at the ocular portion 14 is maintained unchanged and the brightness of the peripheral region of the image is reduced. This would further promote the ununiformity in brightness. Moreover, as the luminous flux is further restricted from the condition shown in FIG. 6, the central region Ac is shielded, but the peripheral region Ar is shielded more than that. This would not make it possible to relieve the ununiformity of the brightness, but would result in an insufficiency of the entire brightness. FIG. 7 shows a condition under which the shield elements 102 and 102 reach the optical axis 0 of the luminous flux A. Under the restricted condition, the central and peripheral regions Ac and Ar are, for the first time, shielded at the same rate. Under the restricted condition or a further restricted condition, however, the illumination is impossible.