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Flash tirgers / Wireless Sync / WTF?

Discussion in 'Strobes and Lighting' started by Pyndle, Nov 12, 2019.

  1. Pyndle

    Pyndle Angel Fish

    # of Dives: 100 - 199
    Location: France
    54
    10
    8
    Hi everyone,

    I'm about to upgrade my underwater camera setup and was looking at the different sync methods. There are a few things I really don't understand:

    - Why is there nothing wireless in 2019? Surely it can't be that hard to make and won't drastically increase battery usage, right?

    - As a consolation lot, I checked those new flash triggers that came out. But I never see the max shutter speed we can use them at. I'm using an A6500 and to me, using fiber optic cable means max shutter speed is at 1/160 (due to limitation of the internal flash) and 1/250 if using sync cords. I assume those limitations are irrelevant with a flash trigger, so what would be the max possible with a fiber optic cable? 1/4000 ?

    - Still on flash triggers, how does it cost so much? It's a piece of non-waterproof plastic that gets an electrical signal and lights up a cheap LED, no? I feel like its a 20usd kind of accessory, not a 200-600usd accessory (which is the price range of a real non-underwater flash).

    Any help is welcomed :)

    Thanks!
     
  2. Barmaglot

    Barmaglot Manta Ray

    # of Dives: 100 - 199
    Location: Israel
    604
    226
    43
    You can't use radio triggering in water because it absorbs electromagnetic radiation. Aluminium housings present an additional barrier. It's possible to trigger strobes remotely using light; see Anglerfish triggers - but fiber optics are a far more common and convenient solution.

    Strobe sync speeds are dictated by camera shutter curtain operation. The idea is, to get a proper flash exposure, you need the first curtain to open fully, then the flash fires, and then the second curtain starts to close. However, with exposures faster than a certain threshold, the second curtain starts closing before the front one is fully open, and what you have, in effect, is a strip of light racing across the sensor. If you fire a strobe while doing that, you'll get black bands above and/or below the exposed area. This can be overcome using high-speed sync, which makes the strobe flicker at 40kHz rather than emit a single continuous pulse, but the only underwater strobe to support it thus far has been Olympus UFL-2, which is actually the guts of a land strobe (Olympus FL-36) in a Sea & Sea housing. As such, it is quite weak by underwater strobe standards, and firing it in HSS mode further reduces its power - that's the big drawback of HSS; it drastically reduces the intensity that the strobe produces. The UFL-2 is also long since discontinued. The coming Retra Prime and Retra Pro flashes are promising an HSS mode, but they've been repeatedly delayed - by latest announcement, they're planning to start shipping in January.

    Compact cameras with fixed lenses typically use leaf type shutters rather than curtains, and these are capable of operating much faster. For example, Sony RX100 series cameras can sync with strobes at up to 1/2000s. Note, however, that a full-power flash on a Z-330 or YS-D2 lasts approximately 3 milliseconds, so syncing at speeds faster than 1/320s can cut into your strobe power as well.

    They are a very low volume item, and producing them requires reverse engineering the cameras' flash communication protocol (it's bidirectional) as well as building the proper TTL exposure curves for different models of strobes. If you want a cheap trigger for just manual operation, look here: El-cheepo Nauticam Optical trigger
     
    Pyndle likes this.
  3. Pyndle

    Pyndle Angel Fish

    # of Dives: 100 - 199
    Location: France
    54
    10
    8
    Wow, thank you for this super helpful answer Barmaglot (this is becoming a habit haha :))

    Had to look at a few videos to understand how shutters actually work but this makes sense now. I guess I'll stay at 1/160 for a while given how long it takes to companies to release new gear for underwater photography :(

    In the case of the A6500, it doesn't make sense to switch to an optical trigger, apart from the slight benefit of saving battery I guess?
     
  4. Barmaglot

    Barmaglot Manta Ray

    # of Dives: 100 - 199
    Location: Israel
    604
    226
    43
    A TTL converter can produce a much more accurate exposure than the pop-up flash driving external strobes because it is programmed with the intensity curve of the strobes that it is driving - it differs between models. The xenon bulbs, when triggered, take a bit of time to reach full intensity (something like 0.2ms on the oscilloscope graphs that I've seen), and when the current is turned off, they take longer (over a millisecond) to gradually stop glowing. On less than full power flashes, they may not reach full intensity at all before the current is stopped. The built-in flash has no way of knowing the external strobes' characteristics, while the trigger (at least the UW-Technics one) does. Also, the built-in flash is limited to approximately 1ms duration, while a full dump from most underwater strobes takes over 3ms, so driving TTL with built-in flash puts a hard cap on their actual power capability.

    If you're using less than full power output, most underwater strobes can produce bursts - the xenon tube is driven by capacitors, and if you don't dump their full charge into a single flash, they can produce more flashes almost immediately, until they're run dry - but if you're using the pop-up flash, it takes at least a second or two to recharge between shots, since it is driven by very small capacitors inside the camera. An LED trigger, whether TTL or manual, removes this limitation.

    I'm not 100% positive on this, but I believe that utilizing the HSS mode on the new Retra strobes will require a compatible LED trigger to drive them. It certainly will with Sony cameras, as popping up the flash hard caps the shutter speed at 1/160s.

    I have just received a pre-production UW-Technics converter for Sony in Meikon housings - it appears to work very well with my ST-100 Pro strobes using Inon Z-240 profile, but I haven't yet taken it underwater.
     
    Pyndle likes this.
  5. Pyndle

    Pyndle Angel Fish

    # of Dives: 100 - 199
    Location: France
    54
    10
    8
    I see, that makes sense. Thanks again for the response!
    I never shoot TTL but I see the point for bursts, but the only case where I'd potentially need burst is with a fast moving non-macro subject (Typically a shark), which often is at full power :)
     
  6. Clack

    Clack Angel Fish

    # of Dives: 25 - 49
    Location: NorCal
    10
    1
    3
    Wow, I'm getting overwhelmed with this stuff as well. I'm shooting a6400 in an Ikelite housing and my wife just bought me a YS-D2j for Chrismas which I haven't opened.

    I contacted the guy at UW Technics and he said he'd make me a ttl trigger for my Ikelite housing but it wouldn't work with the YS-D2j and honestly I think I'd need to bore out the Ikelite ports to get enough LED in anyway. The inside diameter of the ports on nauticam are much much larger. And for sharks, the full power recycle time of the strobe is probably close to the on-board flash recycle time anyway, no?

    Maybe start with onboard flash, and fiber optic trigger with ttl but now am reading people saying this is no good on the sea&sea. Camera and housing are used, strobe and connections can be returned. Any thoughts on ttl sync vs this setup vs maybe the 330 instead of YS-D2j?

    Thank you, any direction is helpful as I try to venture away from ambient light.
     

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