Gehmann 530 Rear Iris/aperature Diop .5-3.0mm Iris 0.5 - 3.0mm Much shorter and adjustable over a wider range of 0.5 - 3.0mm The fixed-seat iris works with individually pin-located tempered spring steel leaves The aim-point is precisely maintained through the wider range of adjustment by the introduction of a new system of aperture control operated by varying the pressure of a steel tube against the central aiming ring - this guarantees a perfect circle at any point within the scale Light reflection is kept to a minimum by external and internal matt finishes Gehmann patented so not available from other manufacturers' irises Laser engraved indications 1.5x diopter with -4.5 to +4.5 correction which is removable if required (needs 577thread adaptor)