The invention relates to an approach to angle tuning a thin film, interference filter device in which light is delivered to the filter from a fiber lying off-axis relative to the filter, and to a method of optically coupling such a device. The optical device comprises a lens unit having an optical axis and an adjustable effective focal length. The device also includes a first port disposed on a first side of the lens unit and on a first side of the optical axis, and an optical element disposed on the second side of the lens unit. The optical element has an optical characteristic that is dependent on the angle of incidence on the optical element. The lens unit has an adjustable focal length so light from the first port is incident on the optical element at a desired angle.