If you make home etched PCBs using dry film photoresist, your exposure setup might benefit from a collimating filter. If light is coming at your PCB from all angles, some rays will find their way under the traces on the transparency. Making sure the majority of the light rays are coming from directly above can mitigate this problem and increase resolution.
This filter is designed to slot into the kind of cheap UV nail polish dryer available on eBay.
There are three STL files in the GitHub repo.
filter.stl is the basic CAD design with no thought put into optimising printing.
r1dfilter.stl is sized to fit the build plate of my printer (a Replicator clone), with wall widths optimised so they only require one pass with the print head. However, I recommend you use
fillerfilter.stl is a plain cube with the mounting grooves cut out, but no honeycomb. Load this into slic3r, set infill to 10% honeycomb and set number of horizontal shells to zero. This way slic3r generates the honeycomb structure itself instead of trying to find a path through a honeycomb you provide. It’s much quicker to slice and to print. The print ends up a bit messier (the slicer thinks it’s doing infill), but it works exactly the same.
Slot the filter into the UV source in place of the normal removable bottom. Place above your PCB and expose as normal.