Rb67 sporadic flash sync

Darryl Roberts · Feb 14, 2020

Hi,
I connect a Pocket Wizard Plus X to my RB 67s lens to trigger my reliable Photogenic strobe. It fires on average 6 to 8 frames out of 10.

Is the problem likely the camera or lens? I don't have another lens.

Thank you.

MattKing · Feb 15, 2020

The RB67 lenses have shutters with really robust flash synch circuits, that historically have been heavily used with a lot of high power flashes with high trigger voltages. As a result, there is a really good chance that they present a much higher resistance circuit path to a modern flash trigger than that trigger is designed for.
My 600 volt trigger voltage Bowens monolights will probably work fine with your lens. Your modern flash trigger is designed to protect cameras that would be damaged by my Bowens units.
The shutters in the lenses can be serviced. Whether or not the circuit resistance can be improved through cleaning and adjustment probably depends on the condition of the shutters in your lens(es).

Darryl Roberts · Feb 15, 2020

Thank you. "Flash triggers," the Pocket Wizards?

Darryl Roberts · Feb 15, 2020

Also, same problem with brand new Hensel Integra strobe.

gdavis · Feb 15, 2020

Hit the test button on the pocket wizard that's connected to the lens a bunch of times and see if it works reliably. You can also try plugging the strobe straight into the lens and see how that works. The results will tell you if it's a problem with the radio triggers or not.

If the above indicates the pocket wizards are working reliably, the next easiest thing would probably be to try another sync cable between the lens and PW.

The sync circuit on the RB67 is built into the lens, not the camera, so we can rule out the camera. If the shutter trips, the camera has done all it needs to do to fire the strobe.

One of my RB67 lenses won't trigger the strobe unless I jam the PC cord in there pretty good, but it's usually pretty reliable once it's in there. If the above test indicates that your pocket wizards are working reliably and the cable is OK, then you might want to see about cleaning the PC port on the lens . Beyond that, might need to have a pro look at it.

Darryl Roberts · Feb 15, 2020

gdavis said:
Hit the test button on the pocket wizard that's connected to the lens a bunch of times and see if it works reliably. You can also try plugging the strobe straight into the lens and see how that works. The results will tell you if it's a problem with the radio triggers or not.

If the above indicates the pocket wizards are working reliably, the next easiest thing would probably be to try another sync cable between the lens and PW.

The sync circuit on the RB67 is built into the lens, not the camera, so we can rule out the camera. If the shutter trips, the camera has done all it needs to do to fire the strobe.

One of my RB67 lenses won't trigger the strobe unless I jam the PC cord in there pretty good, but it's usually pretty reliable once it's in there. If the above test indicates that your pocket wizards are working reliably and the cable is OK, then you might want to see about cleaning the PC port on the lens . Beyond that, might need to have a pro look at it.

Thank you much for your insight. It's definitely not the PWs they work 100% with my digital setup. I will try the strobe directly to the lens.

Mamiya_Repair · Feb 15, 2020

When RB lenses come into the shop for flash sync issues, in most cases the problem is in the sync socket or the socket contact. Sockets become worn out with use and give erratic operation. Also, the sockets come loose and cause the spring contact underneath to make a poor connection with the flash sync contact on the shutter assembly. This applies to the "C" lenses and later as the earlier lenses have the sync contact attached to the shutter housing.
All RB lenses coming into the shop get checked for flash contact efficiency on special test equipment and Mamiya specifications are 60% minimum efficiency (100% would be zero resistance when the shutter blades are open). What this translates to is around a 1.5 ohm maximum resistance through the center contact to ground when the blades are open. So if you measure more than that, there is an issue with the socket or the shutter internals. You can easily remove the flash socket by taking out the two screws holding the socket base in place and make the inspection on the socket or the spring contact. My guess is worn socket or socket contact making poor connection to the shutter.

Darryl Roberts · Feb 15, 2020

Mamiya_Repair said:
When RB lenses come into the shop for flash sync issues, in most cases the problem is in the sync socket or the socket contact. Sockets become worn out with use and give erratic operation. Also, the sockets come loose and cause the spring contact underneath to make a poor connection with the flash sync contact on the shutter assembly. This applies to the "C" lenses and later as the earlier lenses have the sync contact attached to the shutter housing.
All RB lenses coming into the shop get checked for flash contact efficiency on special test equipment and Mamiya specifications are 60% minimum efficiency (100% would be zero resistance when the shutter blades are open). What this translates to is around a 1.5 ohm maximum resistance through the center contact to ground when the blades are open. So if you measure more than that, there is an issue with the socket or the shutter internals. You can easily remove the flash socket by taking out the two screws holding the socket base in place and make the test on the socket itself. My guess is worn socket or socket contact making poor connection to the shutter.

Wow, thank you much.

Darryl Roberts · Feb 29, 2020

Follow-up. The Pocket Wizard and the metal cold shoe on the camera don't get along. Removing it from the cold shoe solved the problem.

Rb67 sporadic flash sync

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