When a Lens Extender is used with the FLIR GF309 (furnace camera), the light in the corners of the image is sometimes reduced.

This phenomenon is called vignetting and is normal for these lens extenders. Radiometry in the central part of the image is not affected.

For more information about vignetting see. http://en.wikipedia.org/wiki/Vignetting

This extender is intended for both fixed and non-fixed lens versions of the GF309 camera. It extends the existing 14.5° and 24° lens to achieve a better viewing angle when measuring the temperatures of furnace tubes through viewports.

It also features a heat shield to deflect the heat from the furnace. To achieve a high measurement accuracy, the external optics transmission will need to be entered into the camera firmware.