OPTICAL FILTER ELEMENT Russian patent published in 2015 - IPC G02B5/20 

FIELD: physics.

SUBSTANCE: optical filter element has a positive optical refracting power and has two positions: in and out of the radiation path; the filter element can be placed between a lens and an image and between an object and a lens without changing its focal distance. The focal distance of the filter element is determined by the formula f'_F=(S+d)·(S+d-δ)/δ, where S is the distance on the optical axis between the object or the image and the optical filter element; d is the thickness of the optical filter element on the optical axis, and the value δ is calculated using the formula δ=d·(n-1)/n, where n is the refraction index of the material of the optical filter element for the fundamental wavelength of the operating spectral range.

EFFECT: enabling installation of the same filter element between a lens and an image and between an object and a lens without disrupting the structure of the lens, while maintaining image quality.

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