How does the Dalsa-based backs know the Copal shutter speed?

[torger]

I have a little technical question out of curiousity. To get my Leaf Aptus to synch with the copal shutter I just put the pc sync cable there and it works. The back wakes up fast enough to react on shutter opening thanks to the dalsa sensor I know that, but how does it detect that it closes? I thought the pc sync cable just sent a signal when the shutter opened, not when it closes, right/wrong?

If it does send a signal when it closes, howcome many backs (like Hasselblad) that require wakeup also cannot detect when the shutter closes, but you have to set a fixed shutter speed in the back itself? It seems like incredibly strange design if they just ignore the shutter close signal if there is one, but maybe that really is the case?

[Doug Peterson]

The circuit of the flash sync port remains closed while the shutter is Irving, regardless of shutter speed.

[torger]

The circuit of the flash sync port remains closed while the shutter is Irving, regardless of shutter speed.

Irving? Huh? So the sync port is closed when the leaf blades are moving? I e closed while shutter is opening and also closed while shutter is closing, i e a signal at the start and one at the end. What has made me believe that it only is closed at the beginning of the exposure is for example this diagram:

http://www.alpa.ch/docroot/tmp/940x550_stamp/articles/2009/new-kid-on-the-block/sync/27337948.jpg

...and the fact that for example Hasselblad backs don't understand when the shutter is closing.

[Graham Welland]

Torger,

I don't believe that the graphic is correct for a copal shutter sync at all. On a technical camera the back has no way of knowing whether the shutter is open for 1/500s or 1000s unless notified by a pulse from the sync port.

[torger]

But wouldn't a flash fire twice if there is a pulse (or rather short cut) both at the start and at the end of the exposure?

[Graham Welland]

I think that the confusion here is between flash sync and shutter sync. Those are the two lines on the graphic - one to wake, the other to indicate the start & stop of the exposure itself.

The Kapture Group multi shot / long exposure box is an example of how the wake & duration are handled separately.

[MaxKißler]

The way it makes sense to me, is to imagine that for the time of the exposure a little lever flips over and enables a connection for the electricity to travel through the pc sync port and back to flash unit or digital back and when the shutter closes this connection is interrupted. A flash is only firing once because it receives just one signal. The back knows when to capture because in "large format camera mode" it constantly tries to send electricity through the sync port and captures for the amount of time a connection is established. Don't know whether this makes sense...

[torger]

Sounds very reasonable. Then the remaining mystery is how some backs cannot know when the shutter closes, like the CF22 I used the other day. I understand why a wakeup trigger is needed (hardware issue with KAF sensors), but not why they can't detect end of exposure either but simply has a timer that one needs to set. Maybe because Hasselblad did not think it was an important feature?

[rogerxnz]

This thread is loosely related to a query I have and that is how can I turn a Hasselblad 5xx camera into a digital pinhole camera with an Aptus or Credo back?

I know it can be done with a Phase back because they are triggered by the metal "feeler" that comes out of the rear of the body when a shot is taken to ensure the film slide is absent and they have a button you can press to turn the sensor on and off. But a Leaf back is triggered from the flash synch and that won't be present with a pinhole lens attachment.
Roger

[Doug Peterson]

This thread is loosely related to a query I have and that is how can I turn a Hasselblad 5xx camera into a digital pinhole camera with an Aptus or Credo back?

I know it can be done with a Phase back because they are triggered by the metal "feeler" that comes out of the rear of the body when a shot is taken to ensure the film slide is absent and they have a button you can press to turn the sensor on and off. But a Leaf back is triggered from the flash synch and that won't be present with a pinhole lens attachment.
Roger

0. Set the back to "large format"
1. Unplug the sync cable from the lens.
2. Take a ballpoint pen and hold it against the contacts of the cable sync cable, while doing this uncover the lens.
3. Prior to releasing the ball point pen recover the lens so the sensor is in darkness when you release the ball point pen.

Alternatively you can use the "old style wakeup cable" from Phase One with the Leaf back. This is part #50300131 on our estore. Same end result, but much easier mechanics (just hold the button down for the length of the shot - the very slight camera shake will be hidden by the utter lack of sharpness of the pinhole camera).



See more medium format pinhole images.

[rogerxnz]

Great pinhole photo, Doug, and thank you for the info.
Roger

[yaya]

See also Chris Ireland's article

[Doug Peterson]

See also Chris Ireland's article

Well great Yair. Now my pinhole images look like crap in comparison :-P.