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Adapter compatibility · Various → Various (Tamron-originated standard)

M42 to T-mount adapter compatibility

Mounting a M42 (Pentax / Praktica screw mount) lens on a T-mount (T2) body — the feasibility verdict, AF / IS / aperture-control / infinity-focus outcome, image-circle relationship, official and reputable third-party adapter SKUs, and the caveats worth knowing before you buy.

Verdict at a glance

Speed booster
MFIS lens-onlyAp. wheel

Mount specs

Lens side

M42 (Pentax / Praktica screw mount)

Flange distance
45.46 mm
Protocol
Mechanical only
Type
legacy-SLR

Body side

T-mount (T2)

Flange distance
55 mm
Protocol
Mechanical only
Type
legacy-SLR

The M42lens’s flange distance (45.46 mm) is 9.54 mm shorter than the T-mount body’s (55 mm). A mechanical adapter can only add distance between the lens and the sensor, never remove it, so a plain spacer cannot hold a M42 lens close enough to reach infinity focus. The verdict above calls for a focal reducer (Speed Booster) — its corrective optics bridge the deficit and add roughly a stop of light.

Flange-distance schematic. Two rails share a sensor plane on the right. The T-mount body register measures 55 millimetres; the M42 lens needs only 45.46 millimetres, which is 9.54 millimetres shorter. The orange region marks the deficit a mechanical spacer cannot remove; a focal reducer is required.Sensor planeT-mount body · 55 mmM42 lens · 45.46 mm−9.54 mm short
The T-mount body holds any lens 55 mm off the sensor, but the M42 lens reaches infinity at 45.46 mm — 9.54 mm closer than the body allows. A mechanical adapter only adds distance, so a focal reducer (Speed Booster) is required to recover infinity focus.

Adapter examples

  • Speed Booster / focal-reducer family

Caveats

  • Flange clearance is only -9.5 mm — a plain mechanical adapter cannot reach infinity focus; a focal reducer (Speed Booster) with optical glass is required.
  • Speed Boosters typically widen the effective focal length (~0.71×) and add ~1 stop of light, which can be desirable on crop bodies.

Common questions

Will M42 (Pentax / Praktica screw mount) lenses autofocus on a T-mount (T2) body through an adapter?
No — M42 → T-mount adapters are mechanical only. Focus is fully manual; rely on the T-mount body's focus peaking and magnify-to-focus aids to nail focus.
Does in-lens image stabilization (IS / VR / OS) still work through a M42 → T-mount adapter?
Lens-side only — the M42 lens's IS / VR / OS unit operates, but it cannot synchronise with the T-mount body's IBIS, so the dual-axis stabilisation native T-mount lenses enjoy isn't available. Lens-side stabilisation still delivers most of the practical benefit.
What's the most-recommended M42 → T-mount adapter?
No SKU in our curated catalogue covers M42 → T-mount yet. Adapter examples photographers commonly use include the Speed Booster / focal-reducer family. Pair compatibility is mostly mechanical, so any well-built adapter at the correct flange distance should work — pick on build quality and tripod-foot integration.

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