Canon EF Extension tube

thingiverse

I'm trying to get this tube to fit, but it keeps sliding to the left every time I adjust the lens. It's really annoying and uncomfortable. So, I came up with a solution: adding a tiny pinhole to lock the lens in place. Just keep in mind that if you've got little infill or a light-colored chamber, some of that light might leak through into the space where it shouldn't be.