Method

A borescope guide device for guiding a borescope (10, fig 1) of a thermal imaging camera (12, fig 1) into the interior of a furnace. The borescope guide device has a moveable borescope mounting 24 and is configured to be mounted on the exterior of the furnace. The borescope mounting may be rotatable along a circular track 44, such that the movement of the borescope is constrained to a single degree of freedom. The borescope may move in a continuous path between a first position and a second position causing the borescope to describe a cone (30, fig 1) within the furnace. The borescope may be a rigid borescope; and the movement of the borescope and camera between the first and second positions may be manual or driven by a motor. The borescope may be cooled by cooling gas and inserted through an inspection hole (14, fig 1) of a furnace.