The Fujinon MK 18-55mm T2.9 is a Super 35 cine zoom announced in February 2017 as the first of Fujifilm's MK series, launched in Sony E-mount at around £3,500 in the UK and shipping from March that year. An X-mount version for Fuji's own cameras followed later as the MKX 18-55mm.
It holds a constant T2.9 across the range, weighs just 980g, and behaves like a proper cine optic despite the price: parfocal design, negligible focus breathing, a 200-degree focus throw, standard 0.8-pitch gears on focus, zoom and iris, a fully de-clicked nine-blade iris, plus a macro mode and a user-adjustable flange back. There is no image stabilisation or autofocus - it is entirely manual.
The MK pair effectively created the affordable owner-operator cine zoom category, undercutting traditional cine glass by thousands while covering the FS5/FS7/FX-series generation of Sony documentary cameras. That population of working lenses now feeds a steady used market, and the 18-55mm is the more common and more in-demand half of the pair.
Many used MKs are ex-rental or ex-production workhorses, so run the mechanics before money changes hands: rack focus and zoom end to end feeling for grit or backlash in the gear rings, check the parfocal behaviour holds (zoom in, focus, zoom out - softness suggests the flange-back needs setting), and inspect the rear element and E-mount seat for wear from repeated camera swaps. Confirm the macro switch and iris ring operate smoothly, look for haze or fungus with a torch, and ask whether the flange-back adjustment has been locked off correctly for E-mount bodies.