T-mount to Micro Four Thirds adapter compatibility

T-mount is the one entry in this matrix that is not really a camera mount at all. It is a lens-side interface — the M42 × 0.75 thread Tamron introduced in 1957 and standardised as T-2 in 1962 — with a fixed 55 mm spacing from the thread shoulder to the focal plane. The lens carries no bayonet of its own; it screws into a body-specific T-X adapter ring, and it is that ring which carries the camera mount. For a Micro Four Thirds body you fit a T-MFT ring: the lens threads into the front, the MFT bayonet sits on the back, and because the MFT flange is only 19.25 mm the ring is built as a roughly 36 mm tube that makes up the difference. That leaves a full 35.75 mm of clearance, so infinity focus is never in doubt — the optics always sit at their designed 55 mm regardless of body. But the reason to choose MFT over every other T destination is the sensor: its 2× crop factor is the largest in this matrix, and on long glass a crop factor is reach, which makes this the maximum-reach pairing of the lot.

What you actually mount is all long glass, because that is what T-mount has always been for — and on a 2× sensor those focal lengths become extraordinary. The Vivitar 500 mm f/8 Mirror frames like a 1000 mm lens, the Samyang 800 mm f/8 Mirror MC like a 1600 mm, and the refractive Soligor 400 mm f/6.3 Tele like an 800 mm — all on a body that weighs a fraction of a full-frame system. The Vivitar and Samyang are catadioptric (mirror) designs, astonishingly compact for their reach because the light path folds back on itself; the Soligor is a conventional refractive tele. None autofocuses; all three were built as budget reach for wildlife, the Moon and the Sun, and the MFT crop pushes them straight into planetary, lunar and small-bird territory that a full-frame body would need a far longer, heavier lens to match. A generic mechanical T-MFT ring from Fotodiox, K&F Concept or Gobe costs less than a memory card, and the whole rig — light body, folded-optic mirror lens, cheap ring — is the lightest super-tele kit you can assemble from this catalogue.

The verdict reads Mechanical · MF · no IS · Ap. ring, and every term is honest for this glass — with two nuances the badge cannot show. Focus is manual, set on the lens barrel and confirmed through the body's focus peaking and magnified live view, because there are no electrical contacts anywhere in a T-mount lens or its ring, so nothing passes EXIF, aperture commands or stabilisation data to the body. 'Ap. ring' is true of the refractive Soligor 400 mm f/6.3, which carries a real preset diaphragm — dial the working f-stop on one ring, then a second ring stops down in a quick turn — but it is not true of the two mirror lenses. A catadioptric design has no iris at all: the Vivitar 500 mm and Samyang 800 mm are fixed at f/8, so you set exposure with shutter, ISO and screw-in or rear drop-in ND filters, and you accept the signature ring-shaped 'donut' highlights a mirror lens renders out of focus. The second nuance is MFT-specific and worth knowing: on the small Four Thirds pixel pitch, f/8 already sits at the onset of diffraction, so the fixed-aperture mirror lenses are working near the sensor's sharpness ceiling — they reward bright light, low ISO and careful technique more than the same lens does on a full-frame body.

Stabilisation is where Micro Four Thirds earns its place as the reach destination, because the system carries the strongest in-body stabilisation made. OM System's OM-1 and OM-1 Mark II and the Olympus E-M1 Mark III post some of the highest IBIS ratings of any camera, and Panasonic's Lumix G9 II and GH7 are not far behind; a dumb T-MFT ring tells the body nothing, so you register the focal length by hand in the IS / 'lens info' menu — 500 mm for the Vivitar, 800 mm for the Samyang — and that class-leading sensor-shift then makes 1000 mm- and 1600 mm-equivalent framing genuinely hand-holdable in a way no other T destination can claim (the box-style bodies such as the BMPCC 4K have no IBIS and lean on a tripod). Image circle is a non-issue and in fact an advantage: all three lenses cover full-frame, so an MFT sensor reads only the very centre of their image circle — the sharpest, most evenly illuminated part — with zero vignetting, and the 2× crop is pure reach rather than a compromise.

The honest summary: T-mount → Micro Four Thirds is the maximum-reach, lightest-rig route — the planetary, lunar and small-bird kit, not a precision-AF or cine path. Fit a generic mechanical T-MFT ring, focus by hand on the EVF, accept fixed f/8 and donut bokeh on the Vivitar 500 and Samyang 800 mirror lenses (and keep an eye on diffraction at f/8 on this sensor), reach for the Soligor 400's preset ring when you want a conventional rendering, and register the focal length in the IS menu so the class-leading IBIS helps you hand-hold the long end. The 2× crop turns this catalogue into 800, 1000 and 1600 mm-equivalent reach on a body you can carry up a hill all day — and because T-mount is the de-facto standard for astronomy optics, the same T-MFT ring threads straight onto a telescope's focuser for prime-focus lunar and solar work, where the crop frames the disc larger than any other body in the matrix.