Question Sea & Sea Strobe Settings - Does anyone have a good technical contact at Sea and Sea??

[AllanHarr]

Found this on the internet...
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Sorcery.
That’s the only explanation.

Ok seriously, it is pretty confusing, but I tried to simplify it as much as possible.

The limitation with fiber optics is that the connection is one way only. The external strobe can “listen” to the camera flash, but can’t “speak” back.

With this limitation in mind, manufacturers have come up with two ways to create optical TTL:

1. Use the pre-flash – also known as S-TTL (INON) / DS-TTL / DS-TTL II (S&S)


The Pre-flash on the camera triggers a pre-flash on the strobe.
The camera detects the light coming back to it, and then emits the correct flash power required to light up the subject correctly.
The strobe detects that main flash, and emits the correct light according to that flash.
The strobe knows how to “read” the pre-flash and main flash and convert it to its own power levels.


The result is a well-lit image.
It also allows exposure compensation to fine-tune the flash output.


Nice explanation here on the Inon website.


2. Ignore the preflash, use real time light sensing – also known as Slave TTL.


This is an older type TTL triggering, which was used exclusively on film before the pre-flash was introduced, but also works today rather well, since the camera does still detect in real time the amount of flash on the subject to avoid over-exposure.

What it does, is sense the pre-flash, ignore it, then when the main flash goes off, it mimics it precisely.

To understand how that produces a good shot, you need to understand how a camera flash works.

If you slow down the entire process, you realize the flash actually works as a continuous light for a short amount of time.

The flash starts emitting light. The camera is measuring the light constantly. As soon as the camera senses that there is a sufficient amount of light in the frame according to how it’s set up, it will tell the flash to stop.
This process happens very fast, about 1/20,000 – 1/30,000 of a second.
The external strobe imitates that precisely. It starts emitting light with the internal flash, and stops when it stops.
This method does not allow exposure compensation.


There may be variations of these methods and different control circuits on specific flash units, but this is the main idea.


Read my complete TTL article with some examples here.


Read this to learn exactly how to test if your TTL works

 

[Barmaglot]

I'm confused, how do you run your camera in manual and your strobe in TTL correctly? I thought the camera and strobe both needed to be in TTL (or a TTL adapter attached between camera and strobe) for TTL to work properly.

Flash power output is modulated by its duration, not brightness. Therefore, when your camera needs to fire a flash, it sends a "turn on" signal, then, some time after that, it sends a "turn off" signal, frequently referred to as "quench". From the camera's perspective, it is always electric signals, but then things can get more complicated. The flash can be wired directly to the camera - either by being built-in, as is common on compacts and mid-range cameras, or by connected via hot shoe or the less common nowadays PC (Pronton-Compur) socket, or it can use a converter in between, translating the electrical signals into light via LEDs (as is common in underwater photography) or into radio waves (as is common above surface). In case of using light signals, the flash typically follows the light output of the triggering signal - it turns on when it detects a light pulse, and quenches when that pulse ceases.

Since each camera manufacturer has their own protocol for TTL (i.e. automatic) flash operation, the flash unit must either include the support for this protocol (underwater, this is basically only Seacam supporting Canon and Nikon, and some Sea & Sea flashes manufactured under Olympus brand), or include some kind of converter in the sequence that will speak the TTL protocol back to the camera processor.

If you're using a Sony camera with a built-in flash (any RX100, NEX or A5xxx/A6xxx camera except A6600 and A6700), this flash is your TTL converter. It always functions in digital TTL mode - it fires a brief (i.e. weak) pre-flash, takes a concurrent picture (but doesn't save it), the camera's processor evaluates the output and decides how much flash power it needs to apply for a proper exposure, then fires the flash at that power, takes an image and saves it. If you have an off-camera strobe in DS-TTL mode attached via fiber optics, then it repeats and amplifies both pulses. You can, to a limited extent (+/- 3EV) modify the processor's decision on flash power, both in camera menus and via flash power knob.

If you're using a different camera with a built-in flash, you may have the option to set its power manually via camera menus and/or a knob, typically in increments of 1/128th, 1/64th, 1/32nd, 1/16th, 1/8th, 1/4, 1/2 or full power. If your off-camera strobe is functioning in TTL mode where it is following the triggering flash's duration, then it will flash with the power corresponding to that of the triggering flash - it will turn on when the triggering flash fires, and quench when the triggering flash quenches and stops sending light. The same is true for any camera with a hot shoe and an optical converter that supports this mode of operation, i.e. manual setting of the triggering pulse duration. This allows you to manually control the output of multiple (usually two but sometimes more) off-camera flashes from a single point. This is not possible with the built-in flash of Sony cameras, as it does not support manual operation.

An additional use case for this mode, as already mentioned, is remote strobe operation, i.e. a strobe not mounted directly on your camera, but set up somewhere in the vicinity on a tripod/muck stick, or carried by another diver. You can preset this strobe for manual power, i.e. fire at the power set by its knob when its light sensor detects a triggering signal (your main strobe(s) firing), but this presents a difficulty if you misjudge the needed power while setting up the shot. Since the strobe is out of arm's reach, you either have to swim over and adjust, or somehow signal your assistant(s) to do so. If you set the remote strobe(s) for slave-TTL, however, they will follow the power of your triggering strobe(s), obviating the need for direct adjustment.

I'm not 100% certain, but I suspect that the difference between DS-TTL and Slave-TTL modes on Sea & Sea YS-D2 is in accounting for the triggering flash's actual duration. The built-in flashes on cameras are typically fairly weak, with the actual flash duration at full power being 1ms or thereabouts, whereas the large off-camera units frequently take 3-4ms or longer to execute a full dump of their capacitors, longer for units with circular bulbs. Therefore, if you take the output of an on-camera flash and apply it unmodified to an off-camera strobe, a full dump of the on-camera flash will only produce a 1/4 power output of the external unit, while the 1/2 and full power settings will not be accessible at all. My best guess is that the DS-TTL setting on YS-D2 applies some kind of multiplier to this triggering signal, whereas Slave-TTL setting does not.

 

[AllanHarr]

Flash power output is modulated by its duration, not brightness. Therefore, when your camera needs to fire a flash, it sends a "turn on" signal, then, some time after that, it sends a "turn off" signal, frequently referred to as "quench". From the camera's perspective, it is always electric signals, but then things can get more complicated. The flash can be wired directly to the camera - either by being built-in, as is common on compacts and mid-range cameras, or by connected via hot shoe or the less common nowadays PC (Pronton-Compur) socket, or it can use a converter in between, translating the electrical signals into light via LEDs (as is common in underwater photography) or into radio waves (as is common above surface). In case of using light signals, the flash typically follows the light output of the triggering signal - it turns on when it detects a light pulse, and quenches when that pulse ceases.

Since each camera manufacturer has their own protocol for TTL (i.e. automatic) flash operation, the flash unit must either include the support for this protocol (underwater, this is basically only Seacam supporting Canon and Nikon, and some Sea & Sea flashes manufactured under Olympus brand), or include some kind of converter in the sequence that will speak the TTL protocol back to the camera processor.

If you're using a Sony camera with a built-in flash (any RX100, NEX or A5xxx/A6xxx camera except A6600 and A6700), this flash is your TTL converter. It always functions in digital TTL mode - it fires a brief (i.e. weak) pre-flash, takes a concurrent picture (but doesn't save it), the camera's processor evaluates the output and decides how much flash power it needs to apply for a proper exposure, then fires the flash at that power, takes an image and saves it. If you have an off-camera strobe in DS-TTL mode attached via fiber optics, then it repeats and amplifies both pulses. You can, to a limited extent (+/- 3EV) modify the processor's decision on flash power, both in camera menus and via flash power knob.

If you're using a different camera with a built-in flash, you may have the option to set its power manually via camera menus and/or a knob, typically in increments of 1/128th, 1/64th, 1/32nd, 1/16th, 1/8th, 1/4, 1/2 or full power. If your off-camera strobe is functioning in TTL mode where it is following the triggering flash's duration, then it will flash with the power corresponding to that of the triggering flash - it will turn on when the triggering flash fires, and quench when the triggering flash quenches and stops sending light. The same is true for any camera with a hot shoe and an optical converter that supports this mode of operation, i.e. manual setting of the triggering pulse duration. This allows you to manually control the output of multiple (usually two but sometimes more) off-camera flashes from a single point. This is not possible with the built-in flash of Sony cameras, as it does not support manual operation.

An additional use case for this mode, as already mentioned, is remote strobe operation, i.e. a strobe not mounted directly on your camera, but set up somewhere in the vicinity on a tripod/muck stick, or carried by another diver. You can preset this strobe for manual power, i.e. fire at the power set by its knob when its light sensor detects a triggering signal (your main strobe(s) firing), but this presents a difficulty if you misjudge the needed power while setting up the shot. Since the strobe is out of arm's reach, you either have to swim over and adjust, or somehow signal your assistant(s) to do so. If you set the remote strobe(s) for slave-TTL, however, they will follow the power of your triggering strobe(s), obviating the need for direct adjustment.

I'm not 100% certain, but I suspect that the difference between DS-TTL and Slave-TTL modes on Sea & Sea YS-D2 is in accounting for the triggering flash's actual duration. The built-in flashes on cameras are typically fairly weak, with the actual flash duration at full power being 1ms or thereabouts, whereas the large off-camera units frequently take 3-4ms or longer to execute a full dump of their capacitors, longer for units with circular bulbs. Therefore, if you take the output of an on-camera flash and apply it unmodified to an off-camera strobe, a full dump of the on-camera flash will only produce a 1/4 power output of the external unit, while the 1/2 and full power settings will not be accessible at all. My best guess is that the DS-TTL setting on YS-D2 applies some kind of multiplier to this triggering signal, whereas Slave-TTL setting does not.

Thank you for explaining this so thoroughly. This is precisely what I've wondered about for some time. Excellent!