AVOID GETTING THE CRYSTAL!!!!!!!!!
This is sort of acquired during the play-through but can be missed. It is found in the 2nd/middle/green door, Luminarium Stage, and the second stage of that. Level 2 stage 2.
Look for the signs for the "Camera Room." Enter, which is required for the progression of the level, and then enter the next room and grab the flash from the "Dark Room." Return to the room with the camera, insert the flash, pull the lever and run to the front of the camera.
If you did this quickly, you were automated to turn and stand still before the timer went down. This also helps if have not gotten the crystal yet because you can take the photo as many times as you like. If you do have the crystal, avoid placing it in the doorway.
Exit the camera room and head upstairs to the "Gentleman's Parlor" located upstairs and not the "Gentleman's Private." In the room is a picture that you need to shine your light on. Pop. ACHIEVEMENT. If you see black in the picture, either take another photo or if you placed the crystal, you will have to do the level over again.