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

Mamiya-Sekor C 70mm f/2.8 Leaf Shutter (645)

Mamiya · Mamiya 645 · 1976

single source, unconfirmed

Also known as: Mamiya-Sekor C 70mm f/2.8 · Mamiya Sekor C 70mm f2.8 Leaf Shutter · Mamiya 645 70mm f/2.8 LS · Mamiya 645 70mm f2.8 lens shutter · Mamiya M645 70mm 2.8 · Sekor C 1:2.8 f=70mm · マミヤ セコールC 70mm F2.8 · マミヤ645 70mm F2.8 レンズシャッター

Variants & identification

Variant Mount Years Serial ranges Production
Mamiya-Sekor C 70mm f/2.8 (lens-shutter type) Mamiya 645 — — —
  1. Element counts, angle of view, closest focus, filter size, dimensions and weight are from Mamiya's Mamiya-Sekor C 70mm f/2.8 (Lens-shutter Type) instruction manual (cameramanuals.org) and the C-era lens brochure. Length: the manual says 54.2 mm, the brochure 50 mm; the page shows the manual's figure.
  2. Shutter speeds 1/30 to 1/500 with no B are from the manual's shutter speed ring and the M645 manual's description; the shutter is bypassed by setting the ring to F, when the body's focal-plane shutter is used instead.
  3. The family year (1976) is the year of the M645 1000S, whose instruction manual already describes the 70mm f/2.8 lens with its between-the-lens shutter; the lens is not in Modern Photography's 1975 and 1976 launch lists. No source gives the launch year itself.
  4. Aperture blade count (5) comes only from the Wikipedia lens table; no Mamiya document consulted gives it.
  5. The 70mm f/2.8 E (no shutter, plastic barrel, 285 g, 50 × 70 mm per Hens and the Wikipedia table) is a different lens at the same focal length and aperture; it is excluded from this page's listings.
How to tell them apart (expand)
  • The first leaf-shutter lens of the 645 system and, until the N/L lenses of the second generation, the only one: shutter speeds 1/30 to 1/500 for flash at any speed, cocked by hand for every exposure with the ring at the front of the barrel (Mamiya's manual; Wikipedia)
  • Two ways to use it: speed ring at F and the A/M lever at A, and it behaves as an ordinary Sekor C on the body's focal-plane shutter; speed ring at a number, body set to 1/8 s or longer, and the lens shutter takes the exposure (Mamiya's manual)
  • X-sync terminal on the lens for the leaf shutter; the body's terminal and hot shoe fire only with the focal-plane shutter (Mamiya's manual)
  • A 70mm f/2.8 without the cocking ring and speed ring is the E kit lens, not this lens

Mamiya-Sekor C 70mm f/2.8 (lens-shutter type):

  • Shutter cocking ring with two grips at the front of the barrel, a shutter speed ring marked 500 250 125 60 30 and F, a cable release socket and an X-sync terminal on the lens itself (Mamiya's 70mm f/2.8 manual)
  • Mamiya's manual: 6 elements in 4 groups, 53°, f/22, 0.8 m, 58 mm screw-in filter and hood, 76 mm diameter, 54.2 mm long, 395 g; the C-era brochure gives 50 mm long

Specifications

Formula
Double-Gauss-type standard lens with a between-the-lens shutter, 6 elements in 4 groups (Mamiya's 70mm f/2.8 Lens-shutter Type instruction manual; C-era lens brochure)
Construction
6 elements / 4 groups
Aperture range
f/2.8–f/22
Diaphragm blades
5
Shutter
Between-the-lens shutter, 1/30–1/500, no B; F setting bypasses it for the body's focal-plane shutter
Min. focus
0.8 m
Dimensions
76 × 54.2 mm
Weight
395 g
Filter
58 mm
Years manufactured
1976
Country
Japan
Coating
Multicoated: the C in Sekor C is Mamiya's multicoating mark (Mamiya's brochures)

What reviewers say

Optical Ratings

Aggregated from the reviews above — follow the links for the full picture.

Chromatic aberration
none seen
Vignetting
strong wide open
Optical formula — Double-Gauss-type standard lens with a between-the-lens shutter, 6 elements in 4 groups (Mamiya's 70mm f/2.8 Lens-shutter Type instruction manual; C-era lens brochure)

History

The 70mm f/2.8 was the first-generation Mamiya 645’s answer to its 1/60 s flash synchronisation: a standard lens, a 44 mm equivalent with a 53° angle of view, with a between-the-lens shutter of its own running from 1/30 to 1/500 s, so that electronic flash can be used at any of those speeds. It is a six-element, four-group design focusing to 0.8 m, with a 58 mm filter thread, a screw-in hood, a 76 mm diameter and 395 g. The M645 1000S manual (the body is of 1976) already carries notes on it, the C-era brochure and the 1981 US brochure list it, and it was the only leaf-shutter lens of the system until the second generation’s A 55mm, 80mm and 150mm N/L lenses, after which it dropped out of Mamiya’s lens sheet. No source consulted gives its launch year, so the family year is the 1000S’s.

The lens works two ways. With the shutter speed ring at F and the A/M lever at A it is an ordinary Sekor C and the body’s focal-plane shutter takes the exposure. To use the leaf shutter, the body is set to 1/8 s or longer, the cocking ring at the front of the barrel is turned clockwise until it stops, which opens the blades for viewing and cocks the shutter, the speed ring is set to a number, and the release fires both: the focal-plane shutter opens for its long time, the leaf shutter makes the exposure inside it, and the blades stay closed until the ring is cocked again, which is why the viewfinder goes dark after each shot. Flash then goes to the X terminal on the lens, not the body. A double cable release lets the mirror go up before the leaf shutter fires, and Mamiya’s PD prism, which does not couple to the lens shutter, is used by setting the same speed on the lens and the prism.

Ashley Pomeroy’s is the one review found: sharp in the middle, still good at the edges, no colour fringing he could see, quite a bit of vignetting at f/2.8 and bokeh smoother than the 80mm f/1.9’s without being smooth. He also records what every owner finds, that the body’s shutter still fires with a loud flop, so the leaf shutter buys fill flash and not silence, and that in practice he used it as a plain f/2.8 portrait lens. Forum posters treat it and the later 80mm f/2.8 N/L as the two leaf-shutter choices for outdoor flash, the 70 being the older, all-metal one.

When buying, cock the shutter and fire it at every speed, listen for the change from 1/30 to 1/500, and check that the blades open fully when cocked and close after release; a shutter that will not cock, or blades that stay shut, mean a service. Check the F position disengages the leaf shutter, that the A/M lever still stops the diaphragm down, and that the X terminal is not corroded. Two other lenses share the numbers: the 70mm f/2.8 E, a plastic-barrelled 285 g kit lens without a shutter sold late in the M645’s run, and the autofocus lenses of the 645AF; neither is this lens.

What remains open: the launch year and the year it was dropped, any list price, the blade count of the diaphragm, which only the Wikipedia table gives, and which of Mamiya’s two lengths (50 or 54.2 mm) was measured the same way.

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 taken with the Mamiya-Sekor C 70mm f/2.8 Leaf Shutter (645)
Mamiya-Sekor C 70mm f/2.8 leaf-shutter lens, with the cocking grips at three and nine o'clock (Ashley Pomeroy) — Ashley Pomeroy, via Wikimedia Commons (CC BY-SA 4.0)

Sample photo wanted — shot with a Mamiya-Sekor C 70mm f/2.8 Leaf Shutter (645)? We'd love to feature it (with credit).

Live listings

Asking price, USD: a median of $300 across 14 fixed-price listings on 2026-09-21 (middle half $270–$310). First day tracked.

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

Show 12 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 2026-09-21. Links go to the shop or marketplace that carries the item.

Related: Mamiya-Sekor Fisheye ULD C 24mm f/4 (645) · Mamiya-Sekor C 35mm f/3.5 (645) · Mamiya-Sekor Shift C 50mm f/4 (645) · Mamiya Macro A 120mm f/4 M (645) · Mamiya A 150mm f/3.8 N/L (645)

Sources (13)

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.