Skip to content
lensmount

Adapter compatibility · Various → Arri (industry standard)

M42 to PL adapter compatibility

Mounting a M42 (Pentax / Praktica screw mount) lens on a PL (Positive Lock) 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

PL (Positive Lock)

Flange distance
52 mm
Protocol
Mechanical only
Type
cinema

The M42lens’s flange distance (45.46 mm) is 6.54 mm shorter than the PL body’s (52 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 PL body register measures 52 millimetres; the M42 lens needs only 45.46 millimetres, which is 6.54 millimetres shorter. The orange region marks the deficit a mechanical spacer cannot remove; a focal reducer is required.Sensor planePL body · 52 mmM42 lens · 45.46 mm−6.54 mm short
The PL body holds any lens 52 mm off the sensor, but the M42 lens reaches infinity at 45.46 mm — 6.54 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 -6.5 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 PL (Positive Lock) body through an adapter?
No — M42 → PL adapters are mechanical only. Focus is fully manual; rely on the PL 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 → PL adapter?
Lens-side only — the M42 lens's IS / VR / OS unit operates, but it cannot synchronise with the PL body's IBIS, so the dual-axis stabilisation native PL lenses enjoy isn't available. Lens-side stabilisation still delivers most of the practical benefit.
What's the most-recommended M42 → PL adapter?
No SKU in our curated catalogue covers M42 → PL 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.

Keep exploring