Endoscopes incorporating a beam splitter

This invention relates to endoscopes of the kind incorporating a beam splitter for direct observation and joint observation by means of a folded optical system substantially larger in diameter than the endoscope or for connection of a film or television camera to the folded optical system. According to the invention, an opaque plate is mounted to face the folded optical system relative to the optical axis of a first part of said system in a tubular member the opaque plate having a small perforation arranged to pass light, the light spot of which is formed via a lens via the beam splitter via an achromatic lens with the image of the object in a common plane in a field lens and is guided together with the object image via the lens system of the folded optical system to an eye piece of the latter.

BACKGROUND OF THE INVENTION 
The present invention relates to endoscopes of the kind incorporating a 
beam splitter for direct observation and for joint observation by means of 
a folded optical system of substantially larger diameter than the 
endoscope or for connection of a film or television camera to the folded 
optical system. Hereinafter such an endoscope will be referred to as "of 
the kind described". 
Endoscopic images, which are supplied to the eyepiece of a co-observer by 
means of a beam splitter and a folded optical system, only occupy a 
correct horizontal and vertical position in the eye-piece in one 
particular position of the members of the folded optical system. As soon 
as any movement of the parts of the optical system is necessary for 
comfortable observation, deviations from this position occur and the image 
in the eye-piece is deflected by up to 180.degree. in, for example, an 
anticlockwise direction so that the observer is no longer in a position to 
recognise what part of the image is at the top. 
To eliminate this disadvantage marks have already been made in two parts of 
the folded optical system, that is in the eye-piece and lens parts which 
are made to overlap by swivelling the eye-piece member or by connecting 
links whereby correct positioning of the image for the co-observer occurs. 
It is an object of the invention to provide means whereby the observer is 
able to recognise the actual position of the image and to adjust the image 
horizontally and vertically in the observer's eyepiece. 
SUMMARY OF THE INVENTION 
In an endoscope of the kind described the invention consists in that an 
opaque plate is mounted to face said folded optical system relative to the 
optical axis of a first part of said system in a tubular members said 
opaque plate having a small perforation arranged to pass light, the light 
spot of which is formed via a lens 10 via said beam splitter 3 via an 
achromatic lens 5 with the image of the object in a common plane in a 
field lens and is guided together with the object image via the lens 
system of said folded optical system to an eye piece of said folded 
optical system. 
By means of this arrangement, the image together with the light spot 
appears in upright and correct lateral position in the eye-piece of the 
folded optical system with the light spot lying in juxtaposition above or 
below the image to denote the correct attitude of the image. If the folded 
optical system is moved the image may take up an altered position but the 
light spot also makes the same movement so that it always marks the 
position of the image correctly and thus provides orientation for the 
observer. The image and the light spot can, however, also be brought into 
an upright and laterally correct position again by suitable movement of 
the eye-piece member or also by intermediate members. 
In general the brightness of the room is sufficient to create the light 
spot which forms through the perforation in the disc but the lightness can 
be increased if desired by a lamp to compensate for any possible 
vignetting in the folded optical system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to the drawing, the image received by an endoscope 1 is delivered 
via an ocular 2 to eye 13 of the doctor via a beam splitter e.g. in the 
form of a prism 3 at the desired brightness whereas the same picture is 
reflected with the remaining proportion of brightness into the folded 
optical system 4 of which only the return lens (5) is shown. Then an 
upside-down endoscopic image 7 occurs in the first field lens 6 via 
achromatic return lens 5. The image is passed on via the parts or limbs of 
the folded optical system so that finally an upright, laterally correct 
image appears in a corrected position in the ocular of the folded optical 
system. 
For recognition of displacements of the image and inclinations from an 
upright laterally correct image which occur when the parts or limbs of the 
folded optical system move, the housing is provided with a tubular member 
or support 4a with reference to the endoscope axis of the folding optical 
system. In this tubular member 4a is mounted an opaque plate 8 which is 
provided with a small perforation 9 radially spaced from the center of the 
tubular member. This perforation 9 can be circular, linear, square or 
cross-shaped. The perforation 9 lets light penetrate from the surrounding 
area or from a lamp (not shown) mounted before the tubular member 4a and 
the image thus resulting from the perforation 9 and the light spot from 
the perforation 9 is formed via a lens 10 through the beam splitter or at 
the beam splitter 3, via the achromatic lens 5, in the field lens 6 in the 
plane of the endoscopic image 7 at 11, i.e. in the case of the example, 
below the upside-down image 7. 
When the image and light spot 11 formed by the perforation are 
retransmitted, the spot always turns with the image 7 and always remains 
in the same position in relation to the image until the image appears with 
the spot in the eye-piece of the folded optical system as an upright, 
laterally correct image. If then deviations in the position of the 
endoscopic image occur by movement of a limb of the folded optical system 
the spot 11 always remains in the same position relative to the image and 
gives the observer an orientation reference i.e. the observer will always 
recognise the location of the top of the image. 
The light spot from perforation 9 by reflection under certain circumstances 
at the reflective face of the beam splitter causes the person 13 who is 
observing directly to be dazzled. To avoid this the beam splitter 3 can be 
shielded from the light spot e.g. by an opaque plate 12 and by blackening 
the face of the beam splitter facing the light spot so that the light spot 
is then guided past the beam splitter 3 into the folded optical system. 
The dazzling effect caused by the reflected light spot is, however, 
negligible for the direct observer if the beam splitter operates at a 
split ratio of 50:50 for example. Then the light spot from perforation 9 
can be supplied directly to the beam splitter 3 without shielding as is 
indicated in dashed lines in the drawing.