Edwin Land's original idea behind instant photography was to create a photographic system that was seamless and easy for anyone to use. The first roll film instant cameras required the photographer to use a light meter to take a reading of the light level, then to set the exposure setting on the lens. Then the lens was focused and the subject framed and the picture was taken. The photographer flipped a switch and pulled the large tab in the back of the camera to pull the negative over the positive, through some rollers to spread the developing agent. After the picture developed inside the camera for the required time, the photographer opened the small door in the camera back and peeled the positive from the negative. To prevent fading, the black and white positive had to be coated with a fixing agent, a potentially messy procedure which led to the development of coaterless instant pack film.