VIRMOS Quadrants & mask sets Representative VIMOS masks with their contour features are shown in their exact orientation in the focal plane.

The XY reference system is common to the focal plane and the StencilLaser machine. The dispersion direction is also indicated.
The crosses indicate the position of the optical axis (which is not coincident with the mask centre), while the pink dashed line indicates the 244x279 mm "useful area" corresponding to the instrument FoV. A further horizontal dashed line delimits a square 244x244 mm area around the optical axis.

[GIF: view of 4 quadrants]