Reply To: Use of flash and Trigger I turtle ?

[Nicolas]

Hi Oriane!

To use burst mode underwater with your fibre optics, you need to consider 3 things:

• 1/ the camera’s capability. how many Frames per Second (FPS) can the camera shoot in burst mode. Your D7100 can do 6 FPS.
• 2/ the trigger’s capability: here you have 2 options, use the D7100’s internal pop-up flash, or install a flash trigger like the i-Turtle trigger.
• 3/ the strobe’s capability: can the strobe recycle fast enough for your 6 FPS, which means the strobe’s recycle time must be shorter than 1/6th of a second, or 0.167ms.

Let’s start with #3: your Inon z240, the newest Retras have 2 seconds (or more) of recycle time, so they definitely cannot sustain burst shooting at full power (in fact, there are no strobes who can, even the very fancy HF-1).

The trick is to lower the power of your strobes. As a rule of thumb (it varies per strobe), each time you divide the power of the strobe by 2, you also divide the recycle time, so at quarter power, the strobe recycle 4 times faster, and so on.

I have used a pair of Inon z240 for a long time, and had no problem shooting at 10 FPS for fast bursts (half a second or max 1 second), provided that I was using 1/16th power (EV-4) or less. Then, the recycle time went down from 1.6 seconds (full power) to approximately 0.1 second, which is fine for 10 FPS.

So your Inons are definitely capable of burst shooting, at least if you control their power manually (no TTL).

The problem of TTL is that the strobe has to fire pre-flashes to test exposure, and this impacts recycle time.

Now let’s look at #2:

If you use TTL mode, I am not surprised your D7100’s internal flash cannot sustain burst shooting.

I invite you to set your camera to manual flash power control, and (very important), navigate to the Custom Settings menus, go to “e” section, and from memory the setting is “e3” (flash control for built-in flash). Set it to Manual, and pick the lowest possible power (I can’t remember if it’s 1/64th or 1/128th).

Then, do another test on land, see if your internal flash can fire at a 6 FPS.

If so, problem solved, as long as you use your strobes manually 🙂

HSS mode is something different and has nothing to do with burst shooting. Use HSS when you need a shutter speed faster than your camera’s maximum sync speed (1/250th). But in this mode, your strobes cannot reach their full power. I personally think it is rarely useful underwater.

Hope this helps, let us know how if that worked?

• This reply was modified 1 year, 7 months ago by  Nicolas Remy.