Optical apparatus and sight tube for inspecting turbine engine components

An apparatus for insertion through an opening in an outer casing of a turbine engine and inspection of internal turbine components at elevated temperatures comprising:

• a hollow optical sight tube configured to optically communicate with an interior of a gas turbine engine via a distal end disposed at the interior of the gas turbine engine and a proximal end disposed exterior of the internal turbine components and defined by a first longitudinal wall defining a continuous, even, and concentric interior surface;
• and
• at least two lenses received within the hollow optical sight tube, the at least two lenses fixed to a first portion of the interior surface of the first longitudinal wall at the distal end of the optical sight tube, and not fully contacting a second portion of the longitudinal wall, wherein a space between the second portion and the at least two lenses defines a longitudinal lens cooling groove of each of the at least two lenses, and wherein the cooling groove of each of the at least two lenses are axially aligned along the first longitudinal wall, the lens cooling groove arranged for flowing a cooling medium from a location external to the turbine to cool the hollow optical sight tube at a location at least adjacent the distal end.