Install instructions

How to install your MamiyaPan Pro kit.

Read this whole page once before you start. The conversion is fully reversible, but rushing through any single step is the difference between a working kit and a stuck mechanism. Plan on a full evening of work (or more).

Before you begin

What's in the box

What you'll need from your bench

Compatibility

This kit is designed and supported for the Mamiya 645 Pro film back. Pro backs usually have the red version of the dark slide, and no rubberized texture on the bottom. The 645 Super back uses a similar frame spacing assembly and the kit will physically work on it, but removing and reinstalling the assembly is much harder.

Also, the gate mask alignment relies on injection-molded registration features that are slightly different on Super backs. If you're installing on a Super, expect to center the vinyl mask by eye rather than letting the molding do it for you. No support is offered for the Super beyond what's on this page.

Phase 1 - Remove the back from the camera and open it up

  1. Photograph the back before starting, all sides. Before any screws come out. If something goes wrong later, these photos are the reference for what the cover, plates, and dials are supposed to look like.
  2. Remove the right side plate. Remove the screws holding the plate in place, keeping their positions documented with your phone photos. With those out, push the back's release knob gently in the direction of its arrow to clear the plate.
  3. Remove the top cover. Remove the screws holding the top cover, then push the cover up to peel it off the adhesive holding the ISO/ASA leadwires. Slacken the leadwires carefully so you don't strain them - they're delicate.
  4. Photograph the internal layout before touching anything inside. This is your reference for how the frame spacing assembly, counter disc, springs, and lever plate all sit together.
  5. Remove the frame counter disc and return spring. Photograph the spring routing first, then lift the counter disc and spring out and set them aside together. The spring is small and easy to misplace.
  6. Remove the lever plate above the frame spacing disc. This is the small plate/bridge carrying the levers and posts that connect the shutter-advance motion to the lever riding on the disc teeth. Photograph it before removal, then lift it out carefully as a unit. Don't bend the levers.
  7. Confirm the frame spacing assembly is now exposed. You should be able to see the three-layer disc/gear stack described in Phase 2.
  8. Remove the E-ring holding the frame spacing assembly down. Cup your hand over it or work inside a tray; E-rings love to launch themselves across the room. Once the E-ring is off, the frame spacing assembly can lift straight out.

Stay focused on the frame spacing assembly. You only need to remove the access parts above it: the frame counter disc, its spring, and the lever plate. If you find yourself removing unrelated gear stacks, springs, or friction parts, stop and compare against your reference photos before going further.

Phase 2 - Disassemble the frame spacing assembly (the hard part)

The frame spacing assembly is three layers stacked on a brass bushing: a small black gear on top (Part A), the OEM 9-notch frame spacing disc in the middle (Part B - the part you're replacing), and a white plastic gear underneath (Part C). A small wire coupling spring connects Part C to Part B - don't lose it.

The brass bushing has a small retaining flange at one end that locks Part C onto the stack. You cannot pull Part C off the bushing without removing this flange first - and pulling harder is exactly how Part C breaks. It's plastic, it's pressed against a brass shoulder, and it has cracked multiple times during testing on this very project. Don't let this happen to you.

The fix is to remove the flange, not fight it. Two methods:

Method A - Dremel with 4.8 mm grinding stone (tested / recommended)

This is the method I've personally tested. Use a Dremel rotary tool with the Dremel 84922 Silicon Carbide Grinding Stone, 4.8 mm. The goal is to remove only the small brass retaining flange so Part C can slide off the bushing. Do not drill out the bushing, and do not grind the plastic gear.

  1. Lift the entire frame spacing assembly straight out of the back and keep it over your tray.
  2. Hold the assembly between your fingers, flange end out. Run the Dremel at low to medium speed. Touch the stone to the brass flange only - keep it off the plastic of Part C.
  3. Grind in light passes. Stop every few seconds, wipe the brass dust away, and check whether Part C has freed up. The flange is small; this should take well under a minute. Once Part C lifts off, you're done.
  4. Wipe the bushing clean of brass dust before reassembly so nothing migrates onto the disc faces.
  5. Set Part C and Part A aside in your tray. The small wire coupling spring goes with them. Part B is the OEM frame spacing disc - save it, it's how you revert later.

Method B - Cutting broach (budget / slower alternative)

A watchmaker's cutting broach should be able to remove the flange more gradually by enlarging the bushing bore from the flange end. This is cheaper and probably less jumpy than a rotary tool, but I have not personally validated it yet. If you use this method, work slowly and stop as soon as Part C lifts off freely.

  1. Lift the frame spacing assembly out of the back as in Method A.
  2. Hold the stack so the brass flange faces up. Insert the smallest broach into the bushing bore, twist it a quarter turn, withdraw, advance to the next size up, and twist again. Work up in steps.
  3. Stop when Part C lifts off freely. The flange is now thinned to zero. The bushing itself is fine - it just lost the lip that held everything together for handling.
  4. Set Part C and Part A aside in your tray. The small wire coupling spring goes with them. Part B is the OEM frame spacing disc - save it, it's how you revert later.

Either method removes the flange permanently. The flange's only job is handling-time retention - keeping the stack together when it's out of the back. You don't lose anything functional by removing it. You just need to handle the stack carefully during the swap because it'll fall apart in your hand if you're not over a tray.

Phase 3 - Swap the disc and reassemble

  1. Confirm orientation. The new 18-notch disc orients the same way as the OEM 9-notch disc - small drive hole and arc slot on the same side, notch profile facing the same way. Compare them flat on your bench before stacking.
  2. Restack A → B (new) → C onto the brass bushing. Re-seat the small wire coupling spring so it connects Part C to Part B - the spring tail engages the small hole on Part B and the matching post on Part C.
  3. Lower the stack into the back in the same orientation it came out. Without the flange, the stack is loose - keep it together with a fingertip until it seats on the housing post.
  4. Reinstall the lever plate above the frame spacing disc. Make sure the tooth-riding lever sits against the disc teeth and moves freely when you advance the mechanism.
  5. Reinstall the frame counter disc and return spring. Use your photos to route the spring the same way it came out.
  6. Verify the counter springs back to zero when you would normally open the back. If it doesn't, the return spring isn't hooked correctly - take it off and re-seat it.
  7. Leave the E-ring off for now. In my installs, the surrounding parts retain the frame spacing assembly well enough once the back is reassembled. You can reinstall the E-ring at the end if you want the extra retention, but don't let it slow down the dry-test and troubleshooting loop.

Phase 4 - Dry test the mechanism before film

With the side cover still off, run the back through a functional dry test before loading film. This is not a visual inspection: some burrs are too small to reliably see, but they show up when the advance lever catches, jumps, drops early, or fails to move the frame spacing disc cleanly.

Test the mechanism in a realistic state: the frame spacing assembly installed, lever plate installed, frame counter wheel and return spring installed, and the side cover off only so you can see what's happening. No film or backing paper is needed for this step.

  1. Wind the advance lever through one complete 30-fire cycle. Watch the lever ride across the teeth and watch the frame spacing disc advance.
  2. Look for four specific problems:
    • Catching: the mechanism hangs up partway through an advance. The lever bottoms in a notch and won't release.
    • Jumping / early drop: the lever rides roughly over one tooth, jumps, or drops into the next channel early. This can cause an intermittent non-advance even if the tooth never fully sticks.
    • Non-advance: you fire/wind but the frame spacing disc does not move to the next stop. On film, this would create a double exposure.
    • Slipping: Parts B and C rotate in unison instead of Part C rotating first to load the small wire coupling spring. If the spring never compresses, indexing is unreliable.
  3. If anything catches, jumps, drops early, or fails to advance, stop and mark the exact physical tooth or sector. Don't rely on the displayed frame number; that can shift after reassembly.
  4. If the first cycle is clean, run a second complete 30-fire cycle. You need two clean full dry cycles before loading film.
  5. If both cycles are clean, close the side cover and move to Phase 6 (gate mask).

Don't skip the dry test. This is the step that protects your first roll. A part can look fine and even pass a simple open-stack check, but still show a subtle lever jump under the real counter-dial load.

Phase 5 - Troubleshooting (only if Phase 4 found something)

Skip this section if you got two clean full dry cycles. If you saw a catch, jump, early drop, non-advance, or slipping behavior, use this playbook.

For a catching, jumping, or non-advancing tooth

This is the main failure mode the dry test is designed to catch. The problem is usually a tiny localized burr or uneven texture on one tooth or sector. It may not be proud enough to make the mechanism fully stick, but it can still make the lever jump or drop early under load. The fix is targeted: sand only the marked tooth or sector, not the whole disc.

  1. Remove the assembly again (Phase 3 in reverse).
  2. Use the included sandpaper on the marked tooth/sector only. The goal is to remove the tiny high spot or uneven texture causing the lever to catch or jump, not to reshape or polish the whole tooth.
  3. Make a few very light passes, then stop. The bad spot may be hard to see by eye, so use the dry-cycle test as your guide: sand a little, reassemble, and test again.
  4. Once the catch or jump is gone, run two complete clean 30-fire dry cycles in the same realistic assembly state before you close the back and load film.

Don't over-sand. If you grind too much off, you can swap a catching tooth for a slipping tooth - the lever no longer grips reliably and you'll get inconsistent indexing instead of catching. The mechanism has a real Goldilocks zone. Make small passes. Test. Repeat.

For slipping

Slip mode means the lever isn't getting enough grip on one tooth. It is less dramatic than a hard catch, but it can still produce inconsistent indexing. The fix is still targeted surface work, not sanding the whole disc.

  1. Mark the offending tooth.
  2. Use the included sandpaper on the catch wall of that notch only (the steeper, near-radial side). A few light passes are enough. You're trying to add a little bite for the lever, not remove material aggressively.
  3. Reassemble and re-run the dry test. Once it passes, run two complete clean 30-fire dry cycles before loading film.

If the problem does not localize to one tooth

Stop and contact support. Don't start sanding multiple random teeth, and don't polish the whole disc. Send photos or video of the open-side dry test to support@mamiyapanpro.com so I can tell whether this is a part issue, an assembly issue, or something else in the back.

Phase 6 - Install the gate mask

The gate mask reshapes the film gate from the full 645 frame to the panoramic frame shape. It is roughly 2.7:1, matching the XPan-style panoramic look while leaving a little real-world alignment tolerance. It's a two-material hybrid: a self-adhesive vinyl base does the bulk masking, and two rigid PET strips define the precision frame edges.

  1. Remove the front panel (the lens-side panel of the back). Watch for a small loose peg on the bottom-right of the panel as it comes off - it's easy to lose. (Pro back only; Super backs don't have it.)
  2. Apply the vinyl mask to the film-facing side of the panel, adhesive down. The window edges of the mask should line up with the raised plastic features from the panel's injection molding. Note the two thin vertical plastic strips connecting the masking strips - the narrower one goes on the darkslide side (left).
  3. Smooth out the seams thoroughly on the darkslide side. Any crease here will catch the darkslide on insertion and may eventually tear the vinyl. Spend an extra minute making this side perfectly flat.
  4. Reinstall the front panel onto the back. Adhesive side of the vinyl is now exposed on the lens side. Secure with a few screws (don't tighten everything yet).
  5. Insert the darkslide. It acts as a rigid base for applying the PET strips.
  6. Apply the PET masking strips onto the exposed adhesive. The rounded corners go into the corners of the original gate, not the masked window. The vinyl window is intentionally oversized; the strips are the precision layer that defines the actual frame edges. The strips are intentionally cut slightly oversized so they can be fit to each individual back. Test-fit each strip first. If it bows instead of lying flat, trim or sand only the left/right ends until it drops in cleanly.
  7. Smooth everything out. Verify the result looks symmetrical. Both strips should be parallel, the gap between them should be consistent end to end.
  8. Tighten all panel screws and remove the darkslide. Test that the darkslide goes in and out smoothly without catching. If it catches, the vinyl seam on the darkslide side is the culprit - remove the panel and re-smooth that edge.

If a PET strip bows, fit the ends - not the image edge. The strips are deliberately oversized because old backs vary. Trim the short left/right ends with sharp scissors, or lightly sand them, until the strip sits perfectly flat against the adhesive. Do not alter the long square edge facing the panoramic window; that edge defines the frame boundary. Small fit-to-back adjustments on the short ends are normal, not a defect.

Phase 7 - Install the viewfinder overlay

The overlay sits on top of the focusing screen and shows you the half-frame composition through the viewfinder. It's a clear transparency with two thin black lines defining the panoramic frame in the finder.

  1. Detach the prism / viewfinder from the camera body, following the standard Mamiya 645 Pro procedure.
  2. Place the overlay on top of the focusing screen, transparency side up. The overlay is non-adhesive - the weight of the prism holds it in place.
  3. Verify the overlay sits flat and is centered. The black lines should be parallel to the long axis of the gate.
  4. Reinstall the prism. Look through the viewfinder. You should see a 2.73:1 panoramic frame defined by the two black lines.

Phase 8 - First roll

  1. Run the full dry test before loading film. After the side cover is back on, wind through two more complete dry cycles if anything about the final assembly felt different. At minimum, do not load film unless Phase 4 has already produced two clean full 30-fire cycles.
  2. Decide whether to reinstall the E-ring. This is optional. In my experience the back works without it once the surrounding parts are back in place. If you want the extra retention, reinstall it now; if it fights you, leave it off and continue.
  3. Use cheap film for your first roll. A roll of Kentmere or a cheap color stock. If something is going to go wrong, you don't want it to be on a roll of Provia.
  4. Wind slowly. Fast, aggressive winding can cause the lever to skip a notch in marginal installs. Smooth, deliberate strokes give the spring its full dwell time.
  5. Count your frames. A correctly installed kit gives you 30 exposures. If the frame counter rolls past 15 and stops at 30, you're golden. If it stops short, the frame spacing disc is skipping somewhere in the cycle - go back to Phase 3.
  6. Develop and inspect. Look at the negative strip flat on a light table. Frames should be evenly spaced with consistent gaps. Slight spacing variation is normal in old mechanical backs, but repeated overlap or completely missed frames means a Phase 5 visit.

Reverting to standard 645

The conversion is fully reversible. To go back to standard 15-frame 645:

  1. Remove the gate mask (peel off the vinyl, detach the PET strips).
  2. Lift out the viewfinder overlay.
  3. Open the back cover, extract the frame spacing assembly, swap the 18-notch disc back to the OEM 9-notch disc.
  4. Reinstall the assembly, optional E-ring if desired, frame counter disc and spring, lever plate, and covers.

Save the OEM disc. The kit doesn't include a spare for it.

Help

Stuck on a step or seeing a failure mode that isn't covered here? Email support@mamiyapanpro.com with photos of the back, the assembly, and a description of what's happening. The more detail the better. The launch video on No Grain No Gain walks through the install with footage if reading isn't enough.