Infrared emitting surfaces such as a smelt bed in a Kraftchemical recovery boiler can be monitored by a closed circuit infrared camera equipped with a 1.5 micrometer edge filter. The camera power supply is isolated from the heat sensitive camera pick up tube and yoke assembly. This separation also makes it easier to mount and dismount the tube on and off of the boiler. The tube is contained in a housing which is supported by bearings which are slidable on rods attached to the boiler wall. This attachment ensures that the image produced will not change with mounting and dismounting the camera. An image change would result in a waste of smelt bed chemicals.