Hello,
IM can handle more than 4 images. Once placed the calibration markers in 4 images you can install other images in the viewports and continue to place markers on those.
Use Ctrl-Left or Ctrl-Right to cycle trough your images.
If you have already calibrated a project you can still load new images in the project.
Place in priority on the new images markers (~features) that are already present on the calibrated shots, and re-calibrate the entire project.
Because the new calibration can be slightly different from the first one, I would advice not to begin modelisation before all images are calibrated.
Stef
