Puzzling feature of the SB-700 speed light

I can use a little help here in understanding the what's going on with the SB-700 when shooting in SU-4 mode as a remote. The settings in this mode are either Auto, manual, or off. The manual states that in the Auto mode, the remote flash sync's with the master (starts and stops with the master). In the manual mode, it only starts with the Master. What is the point of that if you are using Speed lights??? Is this for if your using Auto FP mode or studio lights? or is it something that 'just is' and the next statement below is the more important part of the manual mode?

The manual also states that in Auto, total flash outputs are controlled; whereas in manual, you can set them separately. That part I do understand and can see how it can be applied in photography.

Last thing, In Auto mode, the remote can fire up to 23 feet in front of the master but in manual mode it will work up to 123 feet in front. Why this huge difference???

For all of you out there that could care less about stuff like this, Good for You!!! Wish I could do that sometimes!!

For SU-4 mode, I think you want to set Manual instead of Auto.

Manual is just a regular optical slave, triggers in sync with the triggering manual flash. It is just manual flash, remotely triggered. You set whatever power level you want, manually.

Auto is an old film TTL method, but it is NOT the same for digital iTTL.

Film TTL - there was a sensor in bottom of lens cavity which metered flash reflected from the film surface in real time of exposure. The flash always fired at full power, but when the flash light was deemed sufficient, it quenched the hot shoe flash off, terminating flash exposure. (digital iTTL cannot do that reflection, and instead meters a preflash before shutter opens - very new concepts today, radically incompatible).

Similarly as in the camera, Auto SU-4 mode supposedly could watch the triggering flash (which was controlled by film TTL), and also quench the remote flash off when the triggering flash quit. So, this could be called remote and multiple TTL.

There was no digital preflash to complicate that, but there is in iTTL. And iTTL has its level preprogrammed before the final flash, no quench. Very radically different now. The old film TTL way was normally more accurate, but could not control individual flashes individually. It only saw a final combined result. Whereas, digital Commander never sees a final result, it only sees the individual preflashes, but not how they combine.



You could argue that if using manual flash, you could set the triggering flash to 1/4 power, and set the Auto slave to full power, and the 1/4 power flash ought to quench the remote early too. Timing is determined by duration of all, NOT by intensity of each. For this control, you need to make sure the slave sensor was aimed directly that the main trigger.

Or you could just set both to 1/4 power. Or better, you could just set both to their correct actual level (i.e., metering them individually, etc).


Re: distance. In Auto mode, to turn off, the sensor is battling with its own flash interfering with itself.
In Manual, the scene is dark when it is triggered.

My experience with Manual SU-4 is that it is extremely sensitive, and indoors at least, you can just set it out there anywhere, without concern for where sensor is aimed, or hidden, or line of sight, etc. It will just work. That is far from true with the Commander system, which has to accurately decode a very much more complex signal... which is at minimum power level, instead of full final working level.

FWIW, towards understanding the situation, there is a hardware SU-4 slave

http://www.bhphotovideo.com/c/product/158077-REG/Nikon_3070_SU_4_Wireless_Remote_Slave.html

It existed in film days as an excellent optical slave, but also contributed towards film TTL, for multiple remote flash, in its way. It says for TTL, meaning film TTL, and NOT MEANING digital iTTL.

Same function was included in the later speedlights.

SB-600 and SB-800 were backwards compatible, with film TTL, or D-TTL too, as well as newer iTTL. They could do whatever the camera could do. SB-600 did not include SU-4 function, but SB-800, SB-900, and SB-700 did.

The SB-700 and SB-900 dropped that compatibility, they are digital iTTL only. They left the Auto SU-4 mode however.

Thanks, makes sense. Since I do not have a commander camera (or a sync cord), I need SU-4 mode for off camera flash. To date, I have used it in manual mode and set the flash power where I wanted it. When I starting looking at the auto mode, the manual makes it seem like it works like TTL using a commander. They mention nothing about Film-TTL. Thanks for clarifying that. I will just forget about auto mode in SU-4 mode.

Yes, I have also found the you can put the remote anywhere you want in SU-4 mode and it will fire. I was starting to think that would be the case once I get a 2nd flash and a commander camera (ie. D7100, still wishing!!) and start playing around with the Creative lighting system. Thanks for explaining that more complex pre-flashes are used with the commander function and CLS. I guess radio triggers might also be in my future!!!