Nikon didn’t build a light metering chip into the D40. That’s fine if you’re using one of their auto lenses with the on-board chip. [Matt] decided to add a sensor to his camera and try it out with his manual lenses. His writeup is a bit challenging to get through, but if you’re really into Nikons, you’ll make it. He had to tap into the ribbon cable inside the body, mount the extra hardware, and add an additional switch outside the body to allow the chip to be turned on and off. The extra sensor adds a bit of a step to taking the shot, but it’s the sort of thing that’ll become second nature pretty quickly.