Patent ID: 8306600

Claim:
A filter set for observing fluorescent radiation in biological tissue, the filter set comprising: at least one illumination filter arrangeable in an illumination system of an optical system and having a first wavelength transmission range and a first wavelength blocking range, the first wavelength blocking range comprising wavelengths longer than those comprised in the first wavelength transmission range; and at least one observation filter arrangeable in an imaging system of the optical system and having a second wavelength transmission range comprising wavelengths longer than those comprised in the first wavelength transmission range of the at least one illumination filter and having a second wavelength blocking range comprising wavelengths shorter than those comprised in the second wavelength transmission range; wherein a transmittance for wavelengths in the first wavelength transmission range and the second wavelength transmission range is greater than 0.5, and a transmittance for wavelengths in the first wavelength blocking range and the second wavelength blocking range is smaller than 0.5; wherein a product of the transmittance for wavelengths of the at least one illumination filter and the transmittance for wavelengths of the at least one observation filter in the second wavelength transmission range and the second wavelength blocking range is smaller than 0.05; wherein the at least one observation filter has a third wavelength transmission range comprising wavelengths shorter than those comprised in the second wavelength blocking range; wherein the first, the second and the third wavelength transmission ranges as well as the first and the second wavelength blocking ranges each at least partially comprise the spectral range from 350 nm to 780 nm; and wherein the at least one illumination filter and the at least one observation filter satisfy the following dimensioning rule: X < ∫ 350 Z ⁢ T L ⁡ ( λ ) · T O ⁡ ( λ ) ⁢ ⅆ λ < Y , wherein T L (λ) is the transmittance for wavelengths λ of the at least one illumination filter; T O (λ) is the transmittance for wavelengths λ of the at least one observation filter; X≧0.02 nm; Y≦5 nm; and 480 nm≦Z≦595 nm.