Stumped: iTTL Flash Exposure Lock for Bursts

[ben_hutcherson]

This is one I've been trying to figure out, with no success, for a few weeks now.

Let's say I want to shoot a burst with flash. For the sake of this let's say I'm using flash equipment that can reliably handle moderate frame rates(4-6fps or so-pretty easily achievable if you keep flash power down on a higher powered flash and are using something like a Quantum Turbo).

iTTL, of course, uses a pre-flash to meter the scene. For single shot this isn't really an issue, but it does cause a slight but noticeable amount of shutter lag and also eats into flash power.

Typically, in a burst, frame-to-frame is similar enough that I'd be content with a single iTTL pre-flash at the start of the burst.

I've been driving myself crazy trying to figure this out. I've tried with a couple of different cameras, but mostly find myself trying to do this sort of thing with a D5 or maybe D4 and a Metz 45 CL4 Digital. I have options for flash, though, including a Nikon SB800 or SB900, a Metz 76 MZ-5, and Quantum Q-Flash T5Dr. I'd use any of them if they would let me do this, but I'd also think it would be a camera-side setting...

[Rob Davies]

Are you using button assigned to FV lock to pre-meter?

It's been many years since I've needed to use the feature, but used it years ago with my D3 and SB800 for weddings.

As far as I can remember, the flash value locks until you press the button again.

Apologies if that's a bit vague, but it's been a long time since I used that particular setup.

[hjoseph7]

Why not just use Manual flash power, therefore no pre-flash ? 

[Greg M]

…or non-TTL auto flash, where the flash determines the exposure, meaning no pre-flash needed….

[ilkka_nissila]

FV lock should solve is this issue, if you can take a test shot and then lock it. There are also third-party flashes (Profoto) which give the option of switching from TTL to Manual and the starting point in the manual flash energy settings is equal to the previous TTL result.

[ben_hutcherson]

Thanks everyone, FV lock it is. I assigned it to Fn2, although unfortunately that's a little used button and I'm having a hard time working in pressing it. I may end up putting it somewhere my finger already is anyway most of the time, like center of the multi-selector, although I'll have to see if Fn2 lets me do non-CPU data as an option(one thing I love and hate about Fujis is that any button on the camera is quite literally up for grabs for any control, while Nikon limits some buttons-Fn3 has so much potential IMO but is incredibly limited in what Nikon allows you to assign to it).

I don't know how I'd missed this function, especially in hunting for it.

As for switching flash modes, I do sometimes use multiple off-camera flashes, especially if I'm using the Q-flash behind an umbrella. Switching flash modes is a pretty major ordeal, especially with them high up on a light stand. Manual is viable in some situations, not always where I'd use TTL, though, especially if I'm using stationary lights and with the subject potetially in different positions from burst to burst. The Q-flashes support auto thyristor(I'm using the old Vivitar name for it to avoid confusion, even though I know everyone has their own name) as do the Metz 45 flashes and the SB-800. It works great unless, again, you're off camera behind an umbrella that throws everything back into the eye. They can also end up fighting each other with multiple flashes. I think Quantum lets you designate one as "master" and use its eye for everything, but you need to have them all tied together with physical cords or with with Freewire transmitters to do it.

FV Lock seems the perfect solution for me for now, though.