Can anyone tell me how rear sync is triggered?

We have wired two cables to two land, Nikon SB flash guns using 5 pins on the primary flash and 3 pins on the second flash. They give correct TTL on front curtain sync.

When using rear-sync, the 2nd gun fires a full dump instantly whilst the primary flash gets the correct delay and gives correct TTL.

The N/F 90 manual states that it is not possible to use multiple flash guns in rear sync. (although the older F601 will)

Now my friend has used an underwater Nikon SB104 as the primary gun and now the second land SB gun syncs in rear curtain and its trigger is delayed in sync with the SB104. Both Give correct TTL.

Can anyone tell me what the difference is? What is happening with the triggering?
It is the same wiring, the only difference is the SB104. We have tried 4 different land SB flashes 25/26/28/80DX in different combinations.

I have spoke to Nikon UK and "they don't have that information". I was told to write to Japan!
The only information they could give me is that "rear curtain sync will only work with the flash gun mounted directly on top of the camera". Not true I told them!

The rear sync is important for me as I use it to record/create movement and enables me to get water colour at depth. I have used a S&S YS 90 on slave up to now and it is a hit and miss affair.
A separate slave sensor maybe a solution but I do not know of a Nikon compatible version.

PauP

Email Ike, he'll probably know all about it, plus he has some TTL slave modules too.

SB-28 and SB80DX do not provide their own rear curtain sync control; it must be set on the camera. Rear curtain sync must be set on the SB-24, 25 and 26 strobe; camera setting is ingored. All of these strobes send serial data (pulse codes) to the camera. With this setup, the trigger signal to the strobe is sent when the shutter opens, but there is a delay before strobe actually fires. The delay is determined through the serial data. This exchange of data only happens with the primary strobe.

With the SB-104, there is no serial data sent to the camera. When rear curtain sync is set on the camera, the trigger signal is not sent immediately when the shutter opens; it is sent right before the shutter closes.

Thank you for the reply Ike.

Does that mean if I wire two x SB28 with 3 pins only and use the camera setting for rear curtain, that it may work?
Does the camera need a "ready light" signal/connection?

PauP

Ike
It would be a whole lot easier if your slave sensor worked with Nikonos connections.
ie my housed SB flash gun!

PauP

Please understand that I glean answers from the knowledgeable types. I only know what they tell me and they only tell me what they want me to know. Any knowledge I did have has been forgotten.

Two SB-28 with 3 pins only will not work for rear curtain sync, and the explanation was too confusing for my addled brain. Answer to second question is yes, the camera does need a ready light signal connection to provide TTL.

Some of the brilliance to our SubStrobes is they can operate with rear curtain sync. Our wireless TTL sensor was the first such product in the world, and was to provide one more reason to purchase Ikelite SubStrobes besides their faster recycle time, better battery life, and honest angle of coverage. We did do the Lite-Link for SB24-SB28 strobes which is shown on the Ikelite (www.ikelite.com) web site for multiple strobes above water.