The Dioptrx has a plastic 'C' clip which positions itself in the Televue's EP groove where the rubber eyecup is placed however the Hyperion has a screw thread and small groove. When the Dioptrx eyecup and base are rotated in opposite directions the C clip compresses i.e. the C clip locates itself in the TV's groove while the Dioptrx's C clip compresses itself onto the thread. It just so happens that the diameters are about the same. The bottom line is that it works and the Dioptrx doesn't come off
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Cheers, Steve B