iphone 12 pro heating when using 10x camera for 15 mins

When I use the brand new iphone 12 pro in 10x camera mode for 15 mins, the phone is getting heated . The heat propagates from volume buttons to the back shield of the phone. I didnt even charge the phone nor I inserted SIM or used wifi till now. But I see that heat is considerable may be around 40degC. Anyone face this issue?