Our 6025-format CGH nulls are supported kinematically at 3 corners. If used in a vertical axis configuration, the unsupported 4th corner will sag a bit due to gravity. This gravity sag has no significant effect on the transmitted null wavefront, but it does add diagonal astigmatism to the retro-reflected alignment interferogram that is used to position the CGH null.
The M6025 Skyhook attaches to an M6025 positioner on the side opposite the CGH null. A spring plunger equitably supports the 4th corner of the CGH null by pushing up from below or (by means of a magnet) pulling up from above. The spring force is factory calibrated to equal 1/4 of the nominal weight of a CGH null to compensate the gravity sag. By applying a force and not a constraint, the spring plunger does not degrade the kinematic properties of the M6025 positioner.
The M6205 Skyhook attaches more firmly to the M6025 positioner than to the 4th corner of the CGH null. Also, it is not acted upon by the M6025 release mechanism. Consequently, it will stay in place when you remove the CGH null. The Skyhook also includes captured knurled screws that may be used to attach it even more securely to the M6025 positioner.