Glass Bodies a variant-level encyclopedia of vintage lenses and cameras by iwillpat

Mamiya-Sekor 50mm f/4.5 (RB67)

Mamiya · Mamiya RB67 · 1970

single source, unconfirmed

Also known as: Mamiya RB67 50mm f/4.5 · Mamiya RB67 50mm f4.5 · Mamiya-Sekor 50mm f/4.5 · Mamiya-Sekor C 50mm f/4.5 · Mamiya Sekor C 50mm f4.5 RB67 · Sekor C 50/4.5 · Mamiya Sekor C 50mm f/4.5 FLE · マミヤ RB67 50mm · セコールC 50mm F4.5

Variants & identification

Variant Mount Years Serial ranges Production
Mamiya-Sekor 50mm f/4.5 (1970, single-coated, floating ring) · Seiko #1, T and 1s–1/400, M-X sync Mamiya RB67 1970–1974 — —
Mamiya-Sekor C 50mm f/4.5 (1974, multicoated, floating ring) · Seiko #1, T and 1s–1/400, M-X sync Mamiya RB67 1974–1990 — —
  1. Element and group counts, picture angles, minimum apertures, hoods and weights are from Mamiya's own lens booklets and the RB67 Professional and Pro-S manuals as hosted by butkus.org. Closest-focus figures are from Japanese Wikipedia, which cites Mamiya's catalogues.
  2. Whether a K/L 50mm f/4.5 L was made is not settled by the sources consulted. Mamiya's legacy Pro SD lens page lists a '50mm f/4.5' in the Pro-SD line (11 elements in 8 groups, 81°, closest focus 279 mm, 73 × 94 mm, 780 g) without a K/L prefix, while camera-wiki's lens list and Japanese Wikipedia's KL/L list have no 50 at all. That lens is not entered as a variant here; if it is a K/L, it would carry the removable 7 mm rear ring of the Pro-SD lenses.
  3. Generation start years are those of the bodies the lenses launched with (Professional 1970, Pro-S 1974). No source gives a month for the 50's own changeover, and no discontinuation dates are published.
How to tell them apart (expand)
  • Two name rings: Mamiya-Sekor (1970, single-coated, chrome ring early) and Mamiya-Sekor C (1974, multicoated). Both have the floating ring with its own distance scale on the front of the barrel
  • Slip-on 80 mm square hood shared with the 65, not the screw-in round hood of the longer lenses; 77 mm filter thread on both versions
  • Weight barely separates them: 920 g for the Sekor, 915–920 g for the Sekor C by Mamiya's two figures
  • On the Pro-SD's 61 mm mount both versions want the 7 mm adapter ring Mamiya recommends for light sealing; on the Pro and Pro-S they mount directly
  • Every version carries a Seiko #1 leaf shutter cocked by the body's lever, with cocking pins on the barrel that must be turned fully to the red mark before mounting

Mamiya-Sekor 50mm f/4.5 (1970, single-coated, floating ring):

  • Engraved Mamiya-Sekor 1:4.5 f=50mm with no C after the name; chrome front ring on the early barrels
  • Single anti-reflection coating (camera-wiki); the Lenses for Mamiya RB booklet gives 11 elements in 8 groups, picture angle 82°, minimum aperture 32, slip-on 80 mm square hood, 32 7/16 oz (920 g)
  • A floating ring with its own distance scale on the front of the barrel, and a depth-of-field scale in front of it: the 1970 booklet's page 7 gives instructions for the 50 alone, the only lens in the launch line with the system

Mamiya-Sekor C 50mm f/4.5 (1974, multicoated, floating ring):

  • C engraved after Sekor on the name ring; black barrel; the same floating ring and depth-of-field scale on the front
  • Interchangeable Lenses for Mamiya RB67 booklet: 11 elements in 8 groups, picture angle 82°, minimum aperture 32, slip-on 80 mm hood, 32.2 oz (915 g); the Pro-S manual gives 32-7/16 oz (920 g)
  • Japanese Wikipedia: closest focus 0.279 m, 0.049 m from the front rim, with a close-range correction mechanism

Specifications

Formula
Retrofocus wide-angle with floating front group, 11 elements in 8 groups
Construction
11 elements / 8 groups
Aperture range
f/4.5–f/32
Shutter
Seiko #1 leaf shutter in the lens on both versions: T and 1s–1/400, cocked by the body's lever, M-X flash sync at every speed. No B setting; long exposures use T, closed by turning the speed ring toward 1 second
Min. focus
0.279 m
Weight
920 g
Filter
77 mm
Years manufactured
1970
Country
Japan
Coating
Single-coated on the Mamiya-Sekor; multicoated on the Sekor C of 1974

What reviewers say

Optical formula — Retrofocus wide-angle with floating front group, 11 elements in 8 groups

History

The 50mm f/4.5 was the wide end of the Mamiya RB67’s launch line in 1970 and stayed its everyday wide-angle for twenty years: 82 degrees across the 6 × 7 frame, which Mamiya’s later literature calls the equivalent of 25 mm on 35 mm film. It is also the most complicated lens Mamiya made for the camera at the start, 11 elements in 8 groups and 920 g, heavier than the 180mm f/4.5. Mamiya’s 1970 Lenses for Mamiya RB booklet gives minimum aperture f/32, a slip-on 80 mm square hood and 77 mm filters, and its page 7 is given over to this lens alone, because it is the only one in the line with a floating system. A ring on the front of the barrel with its own distance scale moves a portion of the lens forward or back according to the shooting distance “in order to obtain sharp resolution down to the picture circumference”; nothing changes on the ground glass when it is turned, so the routine is to focus with the body’s knob, read the distance, and set the ring to match. In a hurry, the booklet says, leave it at infinity from infinity to about 2 m and set 1 m for anything nearer.

The multicoated Sekor C of 1974 kept all of that. Formula, angle, hood and floating ring are the same, the weight is 915 g in the lens booklet and 920 g in the Pro-S manual, and Japanese Wikipedia, citing Mamiya’s catalogue, gives closest focus as 0.279 m from the film, 0.049 m from the front rim, on the body’s own bellows. The Pro-S manual adds two rules: nearer than 1 m the lens should be used at f/16 or smaller, and the No. 1 extension tube cannot be used with the 50. Telling the two apart is a matter of the name ring, no C and a chrome front ring for the 1970 lens, C after Sekor for 1974 on; weight will not help. Sellers often add FLE after the name for the C version, a label that is not engraved anywhere on the lens.

What came after 1990 is less tidy. The Pro-SD’s K/L line brought new wides, a 65mm f/4 and a 75mm f/3.5, both with floating elements and ultra-low-dispersion glass, and Mamiya’s legacy page for the Pro-SD lenses also lists a 50mm f/4.5 at 11 elements in 8 groups, 81 degrees, closest focus 279 mm, 73 × 94 mm and 780 g. That page does not call it a K/L, camera-wiki’s lens list has no K/L 50, and Japanese Wikipedia’s KL/L list runs from 65 mm up. The 780 g figure is 140 g under Mamiya’s own weight for the Sekor C, which argues for a different barrel, but no source consulted names it, so it is a table note here rather than a variant. Whichever lens it is, on a Pro-SD it sits on the 61 mm mount; a Sekor or Sekor C on that body wants the 7 mm ring Mamiya recommends for light sealing.

Among the reviewers this catalogue indexes, the 50 is the RB67 lens with the clearest reputation. Scott McClarin’s Emulsive review of the Pro-S singles it out: with the floating ring set and the lens at f/22, hyperfocal at 5.5 ft, everything from half a foot to infinity is sharp, and he calls the Sekor C lenses in general exceptionally sharp while warning that the older lenses show more chromatic aberration. Pablo Cruz Villalba, also on Emulsive, shot it beside the 90 and liked the 50 much more, chiefly for how close it focuses, then gave it a roll of its own to show what he called the power of the lens. Japan Camera Hunter’s system piece reports the argument over whether the C lenses trail the K/L and finds nothing wrong with his own C glass. None of them has compared the 1970 and 1974 versions on film.

The checks are the ones for any RB lens plus one of its own. The Seiko #1 is cocked by the body and can drag at slow speeds or hang at T after years unused; the cocking pins must be turned fully to the red dot before mounting, and both booklets say a lens stored for a long time should have its shutter released. Check the single-coated 1970 lens for separation in its cemented groups. Then turn the floating ring through its whole scale: it should move freely and its distances should match the depth-of-field scale in front of it, because a ring stuck at infinity leaves the corners soft at every close distance the lens was built for. No launch price in yen or dollars for either version was found, and no serial-number table exists.

Expand Collapse

This history is AI-written, from the sources listed at the foot of the page. Where the record is silent it says so rather than filling the gap — but no human wrote these sentences.

Example photos

Sample photo wanted — shot with a Mamiya-Sekor 50mm f/4.5 (RB67)? We'd love to feature it (with credit).

Live listings

Asking price, USD: a median of $300 across 22 fixed-price listings on 2026-09-19 (middle half $270–$350). First day tracked.

Asking prices from the listings scanned, not sales; junk-flagged rows and auction lots excluded; other currencies are not converted.

Show 55 more listings

Buying from Yahoo! Auctions outside Japan. It is a domestic marketplace: sellers ship within Japan, and most will not register an overseas buyer. A proxy service bids on your behalf, receives the item and forwards it, for a fee and a wait. Buyee, Jauce and ZenMarket each accept a Yahoo auction number directly. Listed alphabetically for information — none is recommended over another, and none of these is an affiliate link.

Listings updated 2026-09-19. Links go to the shop or marketplace that carries the item.

Related: Mamiya-Sekor 127mm f/3.8 (RB67) · Mamiya-Sekor 180mm f/4.5 (RB67) · Mamiya-Sekor 250mm f/4.5 (RB67) · Mamiya-Sekor 65mm f/4.5 (RB67) · Mamiya-Sekor 90mm f/3.8 (RB67)

Sources (8)

Every page here is assembled from public sources, and the gaps are real ones. If you own this lens, know a serial number I'm missing, or can see where I have it wrong, tell me — corrections, serials and sample photos are all worth having.