Help with macro-photogrammetry or the art of scanning small objects in the void
Hey everyone !
I've been trying some macro photogrammetry a few times now and I'm always hitting different walls I can't quite solve.
My setup:
I would like to scan an coin on a turntable with a black backdrop(in the void). Im using a Sony 90mm macro lens with ring flash (AR400). Both the lens and the flash are cross-polarized.
Im shooting at 1/60, f/20 with iso at 160.
- Focus drift on rotation
My subject is never perfectly centered on the turntable no matter how careful I am, so as it rotates it slowly drifts out of the focus plane. At f/20 the DOF helps but it's not saving me on the wider objects. Anyone found a good way to nail centering, or is everyone just eyeballing it and accepting some throwaway frames?
- ArUco markers(scale bar) blocking the camera
I use ArUco markers on the plate for scale reference, but since they rotate with the subject, there's always some angle where the marker ends up hidden behind the object relative to the camera. Do you place multiple markers around the perimeter so at least one is always visible? Or is there a smarter placement pattern that avoids this entirely?
https://youtu.be/mMyV\_F\_9Q3E?is=enH5ReC6OvkdvOxt
- Realigning both sides of a coin
This one's been the most frustrating. Since I have to physically hold the coin to scan each face, I end up with two separate scans that need to be stitched together after. The only shared geometry between the two scans is the edge/rim, and it's just too thin and low-feature to get a reliable alignment in software. Anyone dealt with this specific problem ? maybe some kind of holding jig that keeps a consistent reference visible on both scans, or a different capture order altogether?
Would love to hear how people with more experience handle this stuff. Happy to share more rig details if useful.