A versatile on-axis visualization system for the macromolecular crystallography beamline BM07 at the ESRF.

We describe the design of a new dual-magnification on-axis microscope adapted for actinic illumination on beamline BM07 at the European Synchrotron Radiation Facility (ESRF). The instrument combines two cameras equipped with 50 mm and 150 mm focal-length imaging optics, providing low- and high-magnification views of the sample environment, respectively. In addition, the microscope incorporates two lateral optical ports for laser-light injection and collection of back-scattered fluorescence. The core of the on-axis instrument also supports motorized translations for beamstop alignment/positioning, and aperture positioning. A dedicated video and zoom server performs automatic camera selection according to the magnification requested by the user, digital zoom calculation, image-orientation correction and calibration handling. The server is integrated with the beamline software ecosystem, allowing zoom control and live video display directly through both a standalone graphical interface and the MXCUBE data acquisition webpage. This architecture provides a flexible platform for conventional crystal centring as well as future AI-assisted automatic sample recognition and centring, and enables light-triggered kinetic (including time-resolved) and high-pressure crystallography experiments.