1. An optical system for fluorescence observation, comprising: optics including an ocular, a camera, a display, a light source, a first illumination light filter, a first observation light filter, and a controller; wherein the optics provides a first beam path from the light source to an object region for illuminating the object region, wherein the optics provides a second beam path from the object region to the ocular for imaging the object region via the ocular, wherein the optics provides a third beam path from the object region to the camera for imaging the object region onto the camera, and wherein the optics provides a fourth beam path from the display to the ocular for imaging an image, displayed by the display, via the ocular; wherein the optical system has a first mode of operation, in which the first illumination light filter is arranged in the first beam path and the first observation light filter is arranged in the third beam path; wherein the first observation light filter has, in a wavelength range from 380 nm to 725 nm, a transmission characteristics as follows: at least two non-overlapping transmitting regions of the first observation light filter, each of the transmitting regions having, between a first wavelength and a second wavelength, a mean transmittance greater than a first value; and plural blocking regions of the first observation light filter, the plural blocking regions including: a first blocking region of the first observation light filter having, between 380 nm and a smallest one of the first wavelengths of the at least two transmitting regions of the first observation light filter, a mean transmittance smaller than a second value, and at least one further blocking region of the first observation light filter, each of the further blocking regions having, between the second wavelength of one of the at least two transmitting regions of the observation light filter and the first wavelength of a further one of the at least two transmitting regions of the first observation light filter, a mean transmittance smaller than a third value; wherein the first illumination light filter has, in a wavelength range from 380 nm to 725 nm, a transmission characteristics as follows: plural transmitting regions of the first illumination light filter, the plural transmitting regions including: a first transmitting region of the first illumination light filter having, between 380 nm and a wavelength smaller than the smallest one of the first wavelengths of the at least two transmitting regions of the first observation light filter, a mean transmittance greater than a fourth value, and further transmitting regions of the first illumination light filter, each of the further transmitting regions having, between a wavelength greater than the second wavelength of a transmitting region of the first observation light filter and a wavelength smaller than the first wavelength of a further transmitting region of the observation light filter, a mean transmittance greater than a fifth value; and plural blocking regions of the first illumination light filter, each of the blocking regions of the first illumination light filter having, between the wavelength smaller than the first wavelength of one of the transmitting regions of the first observation light filter and the wavelength greater than the second wavelength of this transmitting region of the first observation light filter, a mean transmittance smaller than a sixth value; wherein the controller is configured to process a fluorescent light image obtained by the camera in the first mode of operation by identifying a contiguous fluorescent region in the fluorescent light image obtained in the first mode of operation based on at least one decision parameter, generating a representation of a boundary of the contiguous fluorescent region, generating an image including the representation of the boundary of the contiguous fluorescent region, and supplying the generated image to the display.