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

Mamiya-Sekor Fisheye ULD C 24mm f/4 (645)

Mamiya · Mamiya 645 · 1981

single source, unconfirmed

Also known as: Mamiya-Sekor Fisheye ULD C 24mm f/4 · Mamiya Sekor C 24mm f/4 Fisheye ULD · Mamiya 645 24mm f4 Fisheye · Mamiya Sekor ULD C 24mm f4 · Mamiya M645 24mm fisheye · マミヤ セコール フィッシュアイ ULD C 24mm F4 · マミヤ645 24mm 魚眼

Variants & identification

Variant Mount Years Serial ranges Production
Mamiya-Sekor Fisheye ULD C 24mm f/4 Mamiya 645 — — —
  1. Element counts, angle of view, closest focus, dimensions and weight are from Mamiya's N-era 645 Interchangeable Lenses instruction sheet (Butkus library), which lists the lens as Fisheye C 24mm f/4 without an N suffix; the M645-era instruction sheet gives the same 785 g and 0.3 m. The four built-in filters (LB-A/81C, SL-1B, Y48/Y2, O56/O2) and the equidistant projection are from Mamiya's Sekor C instruction sheet.
  2. The family year (1981) is the earliest dated document consulted, Mamiya's 1981 US brochure, which lists '24mm f/4.0 ULD C'. The lens is absent from Mamiya's early C-era brochure and from the 1975 and 1976 Modern Photography lists, so it arrived between; no source gives the year.
  3. Aperture blade count (5) comes only from the Wikipedia lens table; no Mamiya document consulted gives it. Heublein's serial numbers (10289 to 13295 seen) rest on one source.
How to tell them apart (expand)
  • The only fisheye of the 645 system and the only manual-focus 645 lens with a filter turret: four filters built in, selected by a ring, with no clear position, so one filter is always in the optical path (Mamiya-Sekor C instruction sheet; Heublein)
  • Full-frame image (56 × 41.5 mm) with 180° on the diagonal, not a circular image (Mamiya-Sekor C instruction sheet)
  • Large for the format: 100 mm across and 785 g, with a slip-on cap in place of a hood

Mamiya-Sekor Fisheye ULD C 24mm f/4:

  • Fisheye ULD C on the name ring; a domed front element with no filter thread and a built-in filter turret of four filters, none of which can be removed from the path (Mamiya-Sekor C instruction sheet; Heublein)
  • Mamiya's N-era sheet: 10 elements in 8 groups, 180° diagonal, f/22, 30 cm closest focus, 0.14×, 82 mm long, 100 mm diameter, 785 g

Specifications

Formula
Full-frame equidistant-projection fisheye with ultra-low-dispersion glass, 10 elements in 8 groups (Mamiya's N-era 645 Interchangeable Lenses sheet; Mamiya-Sekor C instruction sheet)
Construction
10 elements / 8 groups
Aperture range
f/4–f/22
Diaphragm blades
5
Min. focus
0.3 m
Dimensions
100 × 82 mm
Weight
785 g
Years manufactured
1981
Country
Japan
Coating
Multicoated: the C in Sekor C is Mamiya's multicoating mark; ULD in the name marks ultra-low-dispersion glass in the formula (1981 brochure; Hens)

What reviewers say

Optical Ratings

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

Flare & ghosting
unshaded dome

History

The Fisheye ULD C 24mm f/4 is the one fisheye of the manual-focus Mamiya 645 system: a full-frame fisheye that covers the 56 by 41.5 mm frame with 180° on the diagonal, using equidistant projection, in which the distance of any point from the picture centre is proportional to its angle from the axis. It is a ten-element, eight-group design with ultra-low-dispersion glass, which is what the ULD in the name records, and it focuses to 0.3 m at 0.14×. The lens is big for a 645 optic, 100 mm across, 82 mm long and 785 g, with a domed front that takes no filter; instead four filters are built in and selected by a ring, LB-A (81C), SL-1B, Y48 (Y2) and O56 (O2), and there is no clear position, so one of them is always in the path.

It is not in Mamiya’s early C-era brochure, which lists twelve lenses, nor in the Modern Photography launch coverage of 1975 and 1976, and it is in the 1981 US brochure as the 24mm f/4.0 ULD C, so it arrived between; no source consulted gives the year. Mamiya’s second-generation instruction sheet lists it without an N suffix, with the same figures, and the maker’s documents describe one version only. Philip Hens’s list has two entries, with and without ULD, on identical figures, and Fabio Heublein reports two examples with different filter sets; that is not enough to write a second variant, and the barrel engraving Fisheye ULD C is what sellers and buyers should expect.

The one review found is Heublein’s on 35mmdealer: only slightly soft in the corners at f/4 and razor sharp to the extreme corners stopped down, with flare in some frames because nothing shades the dome, and a lens that handles best on the small original M645 and awkwardly on the Super and Pro. He also records how rare it is, with weeks when none is listed anywhere, against the double-digit supply of the RB67 and RZ67 37mm fisheye. No bench test was found.

When buying, turn the filter ring through all four positions and look for a scratched or hazed dome, since it cannot be protected by a filter and the cap is the only cover. Check that the A/M lever stops the diaphragm down and that the meter coupling prong is intact. The RB67 and RZ67 37mm f/4.5 fisheyes are different lenses for different mounts and are not covered here; sellers who list a 37mm as a 645 lens are wrong.

What remains open: the launch year, the end of production, any list price, the blade count, which only the Wikipedia table gives, and whether the two filter configurations Heublein saw mark a real production change.

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 Fisheye ULD C 24mm f/4 (645)? We'd love to feature it (with credit).

Live listings

Asking price, USD: a median of $3,100 across 13 fixed-price listings on 2026-09-21 (middle half $2,200–$4,200). First day tracked.

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

Show 2 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 C 35mm f/3.5 (645) · Mamiya-Sekor Shift C 50mm f/4 (645) · Mamiya-Sekor C 70mm f/2.8 Leaf Shutter (645) · Mamiya Macro A 120mm f/4 M (645)

Sources (12)

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.