Continue taking pictures of Little Sisters until you have maxed out the research. It's possible to get this achievement by the end of Hephaestus, but you will more than likely get it during Olympus Heights.
To fill the progress bar as fast as possible, take pictures of the Little Sisters when they are fully in the frame with their Big Daddy. Use the Photographer's Eye tonics to get a 25% research increase to your photos.
You must fill the research bar FIVE times, with a bonus obtained each time you fill it.
You will get a small bonus to your health and EVE bars for each of the five times you fill the research bar.