A method of recording images within a furnace using a thermal imaging camera comprising a bore scope connected to a digital camera unit is described, comprising the steps of: (a) inserting the borescope into the interior of the furnace, (b) collecting one of more images of the interior of the furnace using the thermal imaging camera with the borescope at a first position, and (c) moving the borescope from the first position to a second position and collecting one or more images of the interior of the furnace as the borescope is moved from the first position to the second position, wherein the borescope movement is guided by means of a guide device comprising a movable borescope mounting, mounted externally on the furnace.