Why use a Baveyes M42-MFT instead of a plain M42-MFT adapter?

Two reasons: light gain and field-of-view recovery. M42 lenses are designed for full-frame image circles; on MFT they crop to 2× effective focal length (a 50 mm f/1.4 becomes a 100 mm-equivalent f/1.4). The Baveyes 0.7× reduction reshapes that to ~70 mm-equivalent at f/1.0 — closer to the lens's original 50 mm character with one stop more light. For wides (Mir-1 37 mm, Flektogon 35 mm) the field-of-view recovery is the headline benefit.

How does optical performance hold up at f/0.95 effective on Helios 44-2?

The Caldwell reduction optics are well-corrected on the Helios 44-2 / Pancolar / Super-Takumar primes — corner softness is no worse than the lens's native f/2 performance, and the swirly Helios bokeh character is preserved (sometimes intensified by the reduction). Modern multi-coated M42 lenses (post-1975 SMC Takumars) perform better than older single-coated Russian lenses at the wide-open effective f/0.95-f/1.4 range.

Does it work on every MFT body?

Yes — mechanical / optical adapter only, no electronics to mismatch. Olympus / OM System OM-1 / OM-1 II / OM-5 / Pen E-P7 / Pen E-PL10 and Panasonic G9 / G9 II / GH5 II / GH6 / GH7 / S5 all accept it. The MFT body must be set to manual-focus / manual-exposure mode since no aperture / focus data passes through.

Kipon · M42 → Micro Four Thirds adapter

Kipon Baveyes M42-MFT 0.7x — M42 → Micro Four Thirds adapter

0.7× focal reducer (Caldwell-licensed optics) for M42 screw-mount lenses onto Micro Four Thirds bodies (OM-1 II / OM-5 / G9 II / GH7 / Pen E-P7). ~1 stop wider effective aperture and reduced 2× crop factor (effective ~1.4×).

At a glance

Vendor: Kipon
Release year: 2016
Body-side contacts: None (purely mechanical)
Flags: firmware-updatable —weather-sealed —requires glass

What this adapter preserves

Compatibility for M42 lens on a Micro Four Thirds body (computed from the lensmount dataset — open the M42 to Micro Four Thirds adapter page for the full verdict, flange clearance, and adapter caveats).

Focus: Manual focus only
IS: No IS
Aperture: Manual aperture ring
Infinity focus: Reaches infinity

Format note: Lens covers full-frame; body is MFT — 2× crop factor applies relative to the lens's native image circle. No vignetting; the body uses the centre of the lens.

What it does

Purely optical — no electronics, no AF, no firmware. M42 lens aperture handled by the lens's own ring or stop-down lever. Lets vintage M42 wides (Helios 44-2 58 mm f/2, Mir-1 37 mm f/2.8, Carl Zeiss Jena Flektogon 35 mm f/2.4) regain something closer to their original field-of-view on MFT.

Try your lens through this focal reducer

Pick a lens focal length, max aperture, target body sensor format, and reducer family below — the calc returns the effective focal length, effective f-number, and full-frame equivalent angle of view on that body. Both focal length and f-number scale by the reducer ratio (so the lens always gets two stops faster, distributed as −2·log₂(ratio) stops).

Speed Booster equivalence calculator

Plug in any M42 (Pentax / Praktica screw mount) lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a APS-C body of your choice, plus the full-frame equivalent angle of view after the body's crop stacks on top.

Lens focal length (mm)Max aperture (f/N)Body sensor formatFocal-reducer family

Effective focal length: 35.5 mm
Effective aperture: f/1.28
Full-frame equiv. angle of view: 53.3 mm

A focal reducer concentrates the lens's image circle, so both focal length and f-number scale by the same ratio (stops gained = −2 · log₂(ratio)). The body's crop factor still applies on top — the full-frame-equivalent angle-of-view multiplier is ratio × body crop. Calculator is informational; verify against the adapter vendor's per-lens compatibility chart before purchase.

Common questions

Why use a Baveyes M42-MFT instead of a plain M42-MFT adapter?: Two reasons: light gain and field-of-view recovery. M42 lenses are designed for full-frame image circles; on MFT they crop to 2× effective focal length (a 50 mm f/1.4 becomes a 100 mm-equivalent f/1.4). The Baveyes 0.7× reduction reshapes that to ~70 mm-equivalent at f/1.0 — closer to the lens's original 50 mm character with one stop more light. For wides (Mir-1 37 mm, Flektogon 35 mm) the field-of-view recovery is the headline benefit.
How does optical performance hold up at f/0.95 effective on Helios 44-2?: The Caldwell reduction optics are well-corrected on the Helios 44-2 / Pancolar / Super-Takumar primes — corner softness is no worse than the lens's native f/2 performance, and the swirly Helios bokeh character is preserved (sometimes intensified by the reduction). Modern multi-coated M42 lenses (post-1975 SMC Takumars) perform better than older single-coated Russian lenses at the wide-open effective f/0.95-f/1.4 range.
Does it work on every MFT body?: Yes — mechanical / optical adapter only, no electronics to mismatch. Olympus / OM System OM-1 / OM-1 II / OM-5 / Pen E-P7 / Pen E-PL10 and Panasonic G9 / G9 II / GH5 II / GH6 / GH7 / S5 all accept it. The MFT body must be set to manual-focus / manual-exposure mode since no aperture / focus data passes through.

Mounts on either side

Lens side

M42 (Pentax / Praktica screw mount)

Flange 45.46 mm · Various

Open mount page →

Body side

Micro Four Thirds

Flange 19.25 mm · Olympus / OM System / Panasonic

Open mount page →

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