Optical system for a laser therapy instrument

An optical system for a laser therapy instrument, suitable for laser surgery of a cornea and/or a crystalline lens of an eye, comprising:

• a femtosecond laser radiation source that emits therapeutic laser radiation,
• an objective from which the therapeutic laser radiation exits and is directed and focussed on to or into the eye at a focus position, the objective itself or at least one lens or lens group of the objective being shiftable in the direction of the optical axis relative to other lenses or lens groups of the optical system, the shifting causing a shifting of a focus position from a region of the cornea to a region of the crystalline lens and vice versa,
• at least two optical assemblies that vary the focus of the therapeutic laser radiation, with a focus variation range Δz of the at least two optical assemblies differing in size,
• a changing device that inserts one of the at least two optical assemblies at a time into a therapeutic laser beam path depending on the shifting of the focus position from the region of the cornea to the region of the crystalline lens and vice versa;
• a first optical assembly that covers a first focus variation range Δz1 extending over the axial extension of the cornea, and
• a second optical assembly that covers a focus variation range Δz2 extending over the axial extension of the crystalline lens.