This thread was created at the behest of @Sam_Jacoby as a way to break up the mess that was Laser Flare Illustrated. Specifically to discuss refitting things onto the Form1+ laser path. Please note that actually doing so is both a good way to cause bodily harm to yourself, others, and void your printer’s warranty at the same time.
The following was originally posted here. The “Spatial Filter” of a laser printer is just a bit of metal bent at 90deg with an elliptical hole cut in it. The bit of plastic to it’s right is a double lens. The upper half of which is part of a collimator for the diode. If you look farther back to the laser you can see the two slits there to block yet more unwanted laser light. The first lens (which is glass) in the assembly is hidden under the plastic but you get the idea. The design cost for this whole assembly was probably very high but the end price is something like $100 as a replacement part, mostly because the printer companies would rather sell a new unit that ship these onesy, twosy.
Obviously at 200mW and above you need to move from using plastic in that last lens to something more serious. There is a lot more I could say about this assembly and how costs were cut but that would be way off topic.