How do I activate Thermal Imaging through the Telescopic Lens?

You will notice a button in the bottom right-hand of the screen next to the reload button that has a thermometer icon on it, tap this button and you will activate Thermal Imaging. Now all heat sources, such as enemy soldiers, will be shown as tones of yellows/oranges/reds and anything that is not giving off a heat signature will be shown in tones of blue.

Remember that Thermal Imaging is only currently available for the Sniper Rifle.