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Adapter compatibility · Various → Pentax / Ricoh

M42 to Pentax K adapter compatibility

Mounting a M42 (Pentax / Praktica screw mount) lens on a Pentax K 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
MFno ISAp. ring

Mount specs

Lens side

M42 (Pentax / Praktica screw mount)

Flange distance
45.46 mm
Protocol
Mechanical only
Type
legacy-SLR

Body side

Pentax K

Flange distance
45.46 mm
Protocol
Pentax K (KAF/KAF2/KAF3/KAF4)
Type
DSLR

Flange-distance gap: only 0.00 mm (45.46 mm − 45.46 mm) — thinner than a rigid mechanical adapter can be built to reliably reach infinity focus. The verdict above recommends a focal reducer (Speed Booster) instead of a plain spacer.

Flange-distance schematic. Two rails share a sensor plane on the right. The Pentax K body register measures 45.46 millimetres; the M42 lens needs 45.46 millimetres. The orange region between their left edges is the 0.00 millimetre gap an adapter spans.Sensor planePentax K body · 45.46 mmM42 lens · 45.46 mmflush · 0.00 mm
Both distances right-aligned to the sensor. The gap is only 0.00 mm — thinner than a rigid adapter reliably builds to, so the verdict calls for a focal reducer instead of a plain spacer.

Adapter examples

  • Pentax K-mount M42 adapter (official thin spacer)

Caveats

  • M42 flange 45.46 mm equals Pentax K flange 45.46 mm — Pentax's adapter is essentially a thin alignment ring.
  • Infinity focus preserved exactly; no glass involved.

Common questions

Will M42 (Pentax / Praktica screw mount) lenses autofocus on a Pentax K body through an adapter?
Autofocus is not applicable to this pairing — the M42 mount predates electronic AF, or the bodies in this family do not implement AF for adapted lenses.
Does in-lens image stabilization (IS / VR / OS) still work through a M42 → Pentax K adapter?
Stabilisation is not applicable — M42 lenses in this family do not ship with in-lens stabilisation, or the adapter pair predates the IS protocol entirely.
What's the most-recommended M42 → Pentax K adapter?
No SKU in our curated catalogue covers M42 → Pentax K yet. Adapter examples photographers commonly use include the Pentax K-mount M42 adapter (official thin spacer). 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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