An optical apparatus (10, 110) for high-resolution image transfer through a protective casing, in particular for observation of an outside area, or as an inspection device for observation of an interior; comprising: at least one image-guiding element (30, 130) having a distal end and a proximal end (31, 33); an inverting reflection prism having an entry face and an exit face (51, 52); and a display element; wherein the distal end of the image-guiding element (30, 130) has a light entry face for capturing light beams from the environment; and the proximal end of the image-guiding element (30, 130) has a light exit face for emitting light beams onto the entry face of the inverting reflection prism; wherein during operation of the optical apparatus, the light beams, after having passed through the inverting reflection prism and thereby accordingly having been mirror-reflected with respect to the axis, are directed through the exit face thereof and onto the display element; wherein the image-guiding element (30, 130) is mounted for non-stop rotation relative to the inverting reflection prism and/or relative to the display element over more than 360° about an axis of rotation A that is parallel to the optical axis of the inverting reflection prism, wherein the proximal end of the image-guiding element is mounted for rotation, and wherein rotation is accomplished non-electrically, in a purely mechanical manner; and wherein the surface normal of the light entry face and the surface normal of the light exit face of the image-guiding element (30, 130) enclose an angle μ between 5° and 175°, preferably between 20° and 160°, and most preferably between 30° and 150° between each other; wherein the optical apparatus comprises a housing having a mounting flange, wherein the housing accommodates the inverting reflection prism, and wherein the mounting flange is adapted for being coupled to an outer surface of the protective casing. at least one image-guiding element (30, 130) having a distal end and a proximal end (31, 33); an inverting reflection prism having an entry face and an exit face (51, 52); and a display element; wherein the distal end of the image-guiding element (30, 130) has a light entry face for capturing light beams from the environment; and the proximal end of the image-guiding element (30, 130) has a light exit face for emitting light beams onto the entry face of the inverting reflection prism; wherein during operation of the optical apparatus, the light beams, after having passed through the inverting reflection prism and thereby accordingly having been mirror-reflected with respect to the axis, are directed through the exit face thereof and onto the display element; wherein the image-guiding element (30, 130) is mounted for non-stop rotation relative to the inverting reflection prism and/or relative to the display element over more than 360° about an axis of rotation A that is parallel to the optical axis of the inverting reflection prism, wherein the proximal end of the image-guiding element is mounted for rotation, and wherein rotation is accomplished non-electrically, in a purely mechanical manner; and wherein the surface normal of the light entry face and the surface normal of the light exit face of the image-guiding element (30, 130) enclose an angle μ between 5° and 175°, preferably between 20° and 160°, and most preferably between 30° and 150° between each other; wherein the optical apparatus comprises a housing having a mounting flange, wherein the housing accommodates the inverting reflection prism, and wherein the mounting flange is adapted for being coupled to an outer surface of the protective casing.