So I'm working on a project where we're deciding a new lens to use for our laser diode. I need to determine the appropriate focal length based on the equation: 1/ƒ = 1/μ + 1/σ where ƒ is our focal length, μ is the distance from the lens to image and σ is distance from lens to object. For the purposes of our project we've determined we can assume that our object is infinitely far away and thus we have 1/ƒ = 1/μ or our focal length should be the same as the distance from our lens to our image. Now I just need some help finding that distance. I was looking on the schematic diagram for our laser diode and wanted to determine that distance. I imagined the distance from the "image" to the lens for a laser (as opposed to a camera) would be from the point of emission of the laser to the lens. I've attached a picture of this schematic, if anyone can help me find the distance σ I would truly appreciate it. ** The little distance indicator that I drew in pencil on the diagram is where I believed the distance σ would be. But there's no way to determine this distance from the info given.