MFDB and LF lenses

[David Klepacki]

For any digital back (Phase, Sinar, Leaf, Mamiya), and strictly in untethered operation, can anyone tell me how the shutter speed information from a Copal shutter is provided to the MFDB via the cable that connects them?

 

[Graham Mitchell]

The flash sync cable just communicates when the exposure starts, and when it finishes.

 

[David Klepacki]

Hi Graham, that much I could figure out. What I am asking is how the purely mechanical Copal shutter generates an electronic signal to the digital back. At a minimum, it would need to generate a voltage level difference. How does it do this, especially mechanically at high speed such as 1/500 second? And, is the signal actually held for the duration of the exposure or is it based on two switching "spikes" at the beginning and end of the exposure?

 

[Jack]

The PC synch port on a Copal shutter is just a switch that closes the PC circuit as soon as the shutter starts, stays closed for the entire exposure and then finally opens again after the exposure is over. So basically it's a dumb switch that stays closed for the duration of an exposure, regardless if that exposure is 1 second, 10 seconds on B or 1/500th sec...

The confusion may arise with older shutters that had both an M and X synch switch. The M synch actually had the switch close a bit earlier to allow for the slight delay flash bulbs took to fire. (X synch is current electronic flash and what all modern shutters are synched to.) Real old LF lenses had posts for flash and these are all M synch for bulbs.

 

[jdbfreeheel]

For any digital back (Phase, Sinar, Leaf, Mamiya), and strictly in untethered operation, can anyone tell me how the shutter speed information from a Copal shutter is provided to the MFDB via the cable that connects them?

Just remember too that the Mamiya ZD back does not allow a sync cable; there's no port for it on the ZD. As a result, you can't use the ZD with copal lenses and therefore also, not with any systems such as Alpa, Cambo, Horseman, or the new Sinar Arc system.

I have been in communication with both Alpa and Cambo and they are "waiting" for Mamiya to make an adapter plate, which is referenced on their website in the specs section, for large format work, but it has proved illusive and Mamiya seems to be mum.

 

[Graham Mitchell]

Hi Graham, that much I could figure out. What I am asking is how the purely mechanical Copal shutter generates an electronic signal to the digital back.

Jack already answered it. It creates a simple short circuit.

 

[David Klepacki]

OK, I think I got it now....thanks!

Basically, the sync cord consists of two conductors, and when closed by the shutter completes the circuit to fire the flash.

 

[Jack]

Yup.