A method of detecting an edge of a piece of media in a printer, the method includes providing a carriage for moving a printhead and a photosensor along a carriage scan path; providing a light source; providing a light guiding element having a first end that is aimed at a first predetermined position along a media advance path between a media input region and a printing region and a second end that is aimed at a second predetermined position along the carriage scan path, moving the carriage to an edge-detection position such that the second end of the light guiding element is aimed at the field of view of the photosensor; directing light from the light source toward the first predetermined position; obtaining a signal generated in response to light received in the photosensor; and analyzing the signal to detect the edge of the piece of media.