Praktica B — flange distance, protocol, and adapter compatibility
VEB Pentacon's East-German bayonet replacement for the M42 screw mount, introduced on the Praktica B 200 in 1979. Five electrical contacts in the flange pass open-aperture metering data, but the mount is mechanical for focus and aperture actuation. Native glass: Carl Zeiss Jena Prakticar (Pancolar, Flektogon, Sonnar) plus Pentacon-branded zooms. Production stopped in the early 1990s after the Treuhand wound up Pentacon. Praktica B lenses adapt to mirrorless bodies cleanly; the 44.4 mm flange leaves ample room for adapter thickness.
Mount specifications
Flange focal distance
44.4 mm
Throat diameter
50 mm
Electronic protocol
Mechanical only (no electronic coupling)
Supported formats
full-frame, APS-C
Manufacturer
VEB Pentacon
Introduced
1979 (discontinued)
Status
Discontinued
Praktica B on the flange-distance axis
Praktica B sits at 44.4 mm — highlighted in orange below. The flange-distance gap between the mirrorless and SLR clusters is the room a mechanical adapter occupies; that gap is why almost every SLR lens adapts onto every mirrorless body, and why the reverse is mechanically impossible.
Aperture is selected on the lens's own ring, but the Prakticar diaphragm is automatic — held open by a rear stop-down lever the camera normally actuates at exposure. A mirrorless adapter actuates nothing on its own, so most PB-NEX adapters include a built-in aperture-actuation wheel to press that lever; choose one over a bare ring, or an automatic Prakticar can sit stuck wide open.
26.4 mm flange clearance — comfortable adapter thickness.
Flange clearance is only 0.4 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Canon EF (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only 0.4 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Canon EF-S (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -2.1 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Nikon F (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -0.1 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Sony A / Minolta A (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -1.1 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a M42 (Pentax / Praktica screw mount) (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -1.1 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Pentax K (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -7.6 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a PL (Positive Lock) (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only 0.4 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Canon EF (cine) (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -0.3 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Exakta (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -10.6 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a T-mount (T2) (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only 0.9 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Minolta SR / MC / MD (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -1.6 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Olympus OM (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Flange clearance is only -1.1 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.
Speed Booster equivalence calculator
Plug in any Praktica B lens and pick the focal-reducer family. The calc returns the effective focal length and aperture on a Contax/Yashica (C/Y) (APS-C), plus the full-frame equivalent angle of view after the body's crop stacks on top.
Effective focal length
35.5 mm
50.0 mm × 0.71 on the reducer.
Effective aperture
f/1.28
0.99 stops brighter than f/1.80.
Full-frame equiv. angle of view
53.3 mm
35.5 mm × 1.5× (APS-C sensor crop).
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.
Adapting other lenses onto a Praktica B body
You own a Praktica B body and want to mount glass from other systems. Mirrorless-lens-onto-DSLR-body combinations are omitted (rear element collides with the mirror box).
Flange clearance is only -0.4 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.
Flange clearance is only -0.4 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.
Flange clearance is only -2.4 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.
Flange clearance is only 0.1 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.
Flange clearance is only 1.1 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.
Flange clearance is only 1.1 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.
Flange clearance is only -0.4 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.
Flange clearance is only 0.3 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.
Flange clearance is only -3.9 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.
Flange clearance is only -0.9 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.
Flange clearance is only 1.6 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.
Flange clearance is only 1.1 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.
Pentacon-branded Prakticar zooms (35-70 mm f/3.5, 70-210 mm f/4.5-5.6) and Carl Zeiss Jena primes specifically built for B-mount (Pancolar 50 mm f/1.8 MC, Flektogon 35 mm f/2.4 MC, Sonnar 135 mm f/3.5 MC). Sigma and Tamron also briefly made Praktica B variants in the 1980s. M42 lenses don't fit B-mount directly — the bayonet is incompatible — but M42-to-B adapter rings exist for cross-mounting older Pentacon screw-mount glass.
Can I autofocus a Praktica B lens on a modern camera?
No — Praktica B is mechanical for both focus and aperture actuation. The five electrical contacts pass open-aperture metering data only; there is no AF coupling whatsoever in any Praktica B body or lens. On any mirrorless body via a B-to-mirrorless adapter, focus is fully manual and aperture is set on the lens's external ring.
Are Praktica B lenses worth using on a Sony E or Fujifilm X body?
Mixed. Pancolar 50 mm f/1.8 MC and Flektogon 35 mm f/2.4 MC are well-regarded by users seeking the Carl Zeiss Jena rendering — they're optically equivalent to their M42 siblings. Pentacon zooms are unremarkable. The 44.4 mm flange leaves abundant room for adaptation onto every mirrorless mount via $20-30 dumb mechanical rings; budget alternative to the more sought-after M42 Carl Zeiss Jena equivalents.