Half-frame 645. Thirty panoramic frames per roll.
A replacement dividing device 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.
The mechanism
The Mamiya 645 Pro back's 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.
What's in the kit
- 18-notch dividing device. Laser-cut spring steel. Drop-in replacement for the OEM Part B inside the 645 Pro back.
- 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 dividing-device stack 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.
The mechanism 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 dividing device and you can put the back to standard 15-frame 645 anytime.
Sample frames
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.