Half-frame 645. Thirty panoramic frames per roll.

A replacement frame spacing disc for the Mamiya 645 Pro film back. Same camera, same lenses, same workflow. Twice the frames per roll of 120, in a 2.73:1 panoramic format that's almost identical to the Hasselblad XPan, but on a back you probably already own.

frames per 120 roll

56 × 20.5

mm per frame

2.73:1

aspect ratio (XPan: 2.71)

1.33×

negative area vs 35 mm

The mechanism

The Mamiya 645 Pro back's frame spacing disc - Mamiya's service manual calls it the dividing device - is a stamped metal disc with 9 castle-style notches. Each notch triggers the stop lever once per advance, giving you 15 frames at 56 × 41.5 mm per roll. The MamiyaPan Pro replacement is a precision-cut 18-notch disc sized for half-frame spacing. Twice the stops, twice the frames, same drive train and spring coupling.

OEM disc

9 notches → 15 frames

56 × 41.5 mm · 1.35:1

→

MamiyaPan Pro

18 notches → 30 frames

56 × 20.5 mm · 2.73:1

What's in the kit

18-notch frame spacing disc. Laser-cut spring steel. Replaces the 9-notch OEM disc inside the 645 Pro back's frame spacing assembly.
Gate mask. Two-material hybrid (self-adhesive vinyl base plus rigid masking strips) that reshapes the film gate from full 645 to half-frame.
Viewfinder overlay. So the camera shows you what you're actually capturing, not the unmasked 645 frame.
Sandpaper plus printed instructions. Including a troubleshooting guide for catching or slippery teeth.

Honest install notes

This is a tinkerer's kit, not a drop-in accessory. The film back has to come off the camera, the frame spacing assembly has to be partially disassembled to swap the OEM disc for the new one, the gate mask has to be aligned and stuck down, and the viewfinder overlay seated. You supply your own light grease (Krytox or equivalent). Plan on an evening at the bench. Read the full install guide before you commit.

The disc itself is precision laser-cut, but laser cutting can leave micro-burrs that show up under load. Most kits work as shipped; some need a few seconds of targeted sanding on a single tooth to land in the mechanism's friction sweet spot. The instructions walk through both failure modes (catching vs slipping) and the right fix for each.

The conversion is fully reversible. Save the OEM disc and you can put the back to standard 15-frame 645 anytime.

Sample frames

Boats on the Hudson at sunset — Provia 100F

Portrait of a man in a white suit at blue hour — Provia 100F

Coffee shop scene with foreground bokeh — Portra 400

Brownstone facade with cherry blossom — Provia 100F

Pink cherry blossoms in bloom — Provia 100F

Group playing music in a circle, black and white — HP5 Plus 400

American flags and crosswalk in city light — Provia 100F

Panoramic frame on Portra 400 — Portra 400

Photographer working with a medium format camera — Portra 400

Black and white panoramic frame on Kentmere PAN 100 — Kentmere PAN 100

Black and white panoramic frame on HP5 Plus 400 — HP5 Plus 400

Format comparison

Format	Size (mm)	Ratio	Area (mm²)
35 mm standard	36 × 24	1.5:1	864
35 mm panoramic crop	36 × ~13	2.77:1	468
MamiyaPan Pro	56 × 20.5	2.73:1	1,148
Hasselblad XPan	65 × 24	2.71:1	1,560
Full 645	56 × 41.5	1.35:1	2,324

Status

The mechanism is validated. Multiple test rolls shot, scanned, and printed. First production batch is in the queue. Kits will be limited at first run while I dial in the assembly process. Sign up below to be notified when the first batch is ready, and to watch the launch video on No Grain No Gain when it goes live.