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

Mamiya-Sekor C 300mm f/5.6 (645)

Mamiya · Mamiya 645 · 1977

single source, unconfirmed

Also known as: Mamiya-Sekor C 300mm f/5.6 · Mamiya Sekor C 300mm f5.6 · Mamiya 645 300mm f/5.6 · Mamiya-Sekor ULD C 300mm f/5.6 N · Mamiya Sekor C 300mm f/5.6 N ULD · Sekor C 300/5.6 · マミヤ セコールC 300mm F5.6 · マミヤ 645 300mm F5.6 · セコール ULD C 300mm F5.6 N

Variants & identification

Variant Mount Years Serial ranges Production
Mamiya-Sekor C 300mm f/5.6 Mamiya 645 1977 — —
Mamiya-Sekor ULD C 300mm f/5.6 N Mamiya 645 1988 — —
  1. Optical construction, angle of view, minimum aperture, closest focus, magnification, filter size, hood, dimensions and weight are from Mamiya's own tables: the M645 1000S manual and the Sekor C instruction sheet (both at butkus.org) for the C, and the 645 Pro-era Interchangeable Lenses product sheet for the ULD N. The two versions print identical figures.
  2. Both dates and both yen prices rest on one source, the awane-photo Camera Museum's reading of the Japanese camera-catalogue volumes (vol.58 of 1977, vol.89 of 1987, vol.91 of 1988). No second source dates either version, so the page carries the single-source flag. The M645 launched in June 1975 with no 300 on camera-wiki's original list; the 1977 catalogue is the earliest sighting found.
  3. The 9 aperture blades are Wikipedia's figure; Mamiya's tables give no blade count.
  4. The A 300mm f/2.8 APO of 1992 is a different lens (9 elements in 8 groups, 2,700 g, per Mamiya's product sheet) and has its own page.
How to tell them apart (expand)
  • Two versions, same layout: ULD before the C and N after the focal length mark the second; the first reads plainly Mamiya-Sekor C 300mm
  • 58 mm filter thread and a built-in pull-out hood on both; Mamiya's sheet says the telephoto hoods come out more smoothly if rotated while pulling
  • 710 g and 164 mm long, the same on both versions by Mamiya's tables; Nordhaug weighed his at 710 g and measured 164 mm
  • No shutter-speed ring and no tripod foot; the 500mm f/5.6 has the foot

Mamiya-Sekor C 300mm f/5.6:

  • Name ring reads Mamiya-Sekor C 300mm 1:5.6 with no ULD before the C and no N after the focal length
  • Mamiya's tables: 6 elements in 5 groups, 13° angle of view, f/5.6–32, 4 m closest focus, 0.09×, 58 mm filter, built-on hood, 164 × 70 mm, 710 g
  • Listed in Mamiya's M645 1000S-era manual and on the M645J-era system chart; the Sekor C instruction sheet of the M645 Super years still prints it without an N

Mamiya-Sekor ULD C 300mm f/5.6 N:

  • ULD engraved before the C and N after the focal length on the name ring; plastic aperture ring of the N generation (Wikipedia)
  • Same table figures as the C: Mamiya's 645 Pro-era product sheet lists the C 300mm f/5.6N at 6 elements in 5 groups, 13°, f/32, 400 cm, 0.09×, 58 mm, built-in hood, 164 × 70 mm, 710 g
  • Mamiya's 645 Pro manual names it 'ULD 300mm f/5.6N' in the 1992 lens list

Specifications

Construction
6 elements / 5 groups
Aperture range
f/5.6–f/32
Diaphragm blades
9
Min. focus
4 m
Dimensions
70 × 164 mm
Weight
710 g
Filter
58 mm
Years manufactured
1977
Country
Japan
Coating
Multi-coated on both versions: Mamiya's sheet says 'all the lenses for the M645 have been multi-coated', and the C in Sekor C denotes multicoating (Wikipedia); the ULD N adds an ultra-low-dispersion element
Original price
¥73,500 (1977, C version); ¥106,300 (1988, ULD C N) (today ¥127,000)

What reviewers say

Optical Ratings

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

Chromatic aberration
moderate, correctable
Optical formula

History

The 300mm f/5.6 is the longest of the ordinary telephotos in Mamiya’s manual-focus 645 line, a 186mm equivalent on 35mm film by Mamiya’s table, and the smallest 300 the system offered. Mamiya’s own figures: 6 elements in 5 groups, a 13° angle of view, f/5.6 to f/32, closest focus at 4 m for 0.09×, a 58 mm filter thread shared with most of the line, a built-in pull-out hood, and 710 g in a barrel 70 mm across and 164 mm long. The M645 1000S manual prints a cross-section: a cemented group and two singlets at the front, a small negative group at the rear, a telephoto layout of the plainest kind.

Two versions exist and Mamiya’s tables give them the same numbers. The Mamiya-Sekor C came first: the awane-photo Camera Museum finds it in the 1977 volume of the Japanese camera-catalogue series at ¥73,500, and it is on the M645J-era system chart and in the 1000S manual. The Mamiya-Sekor ULD C 300mm f/5.6 N followed: the same museum entry records it in the 1988 volume at ¥106,300, Mamiya’s 645 Pro manual of 1992 lists ‘ULD 300mm f/5.6N’ among the telephotos, and Wikipedia describes the N generation as a restyled barrel with a plastic aperture ring. ULD is Mamiya’s ultra-low-dispersion glass; the layout, weight and length did not change with it. Both dates come from one source and the page says so.

The one reviewer to compare them directly is Dag Ole Nordhaug, on a 100-megapixel Hasselblad X2D. The C he found ‘quite good’ in the centre, softer in the corners and ‘quite uniform’ overall, with moderate colour fringing that Lightroom removes. The ULD N was noticeably sharper in the centre and at the edges, but, to his surprise, fringed about as much as the older lens. Against the 105-210 ULD zoom at its long end, cropped to the same view, he called the ULD prime ‘a draw’. Forum users on DPReview and MFlenses report the same things in fewer words: very well built, light for a 300, little chromatic aberration, and a lens that needs sun because f/5.6 on a long telephoto asks for shutter speed.

Buying is simple because the versions are marked. ULD before the C and N after the focal length is the later lens; a plain Mamiya-Sekor C 300mm is the earlier one, and some sellers describe a plain N without ULD that no Mamiya document consulted lists. Either takes 58 mm filters and has the sliding hood. Check that the hood slides freely, that the focus ring is not stiff with old grease (the MFlenses example needed it), that the Auto/Manual lever is back on A, and that the aperture blades snap shut. The lens mounts on the 645AF and later bodies but meters only stopped down there. The A 300mm f/2.8 APO is a different, four-times-heavier lens with its own page.

What remains open: a second source for either launch year, whether Mamiya ever sold an N without the ULD element, and a discontinuation date.

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 C 300mm f/5.6 (645)? We'd love to feature it (with credit).

Live listings

Asking price, USD: a median of $150 across 20 fixed-price listings on 2026-09-21 (middle half $110–$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 25 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 APO A 300mm f/2.8 (645) · Mamiya-Sekor C 500mm f/5.6 (645) · Mamiya-Sekor Zoom C 105-210mm f/4.5 (645) · Mamiya-Sekor C 210mm f/4 (645) · Mamiya-Sekor C 150mm f/3.5 (645)

Sources (14)

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.