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TTL flash with mirrorless cameras.


rodeo_joe1

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I can't speak for all mirrorless cameras, but the Sony A7/A9 use a "flakey" pre-flash, and only with the mechanical "rear" chutter. It's highly effective, arguably more accurate than my Nikon SB=900 with a D3. There is also the option of using a sensor in the flash for auto exposure, but the Sony still requires a mechanical shutter.

 

The electronic first shutter can be used. I think the mechanical shutter "clears" the sensor after the pre-flash is read, then the exposure and a second shutter. There is a lot of lag using an A7Rii. The A9 is supposed to be faster, but I haven't tested it yet.

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" the Sony A7/A9 use a "flakey" pre-flash"

- That's disappointing to hear.

 

As I said in another thread: Pre-flash systems assume too much.

1) That the pre-flash is of accurate enough duration to deliver the presumed flash energy.

2) That the calculated flash duration for the main flash also delivers flash energy in the desired proportion to the pre-flash.

 

This system relies a lot on component and flash tube tolerances being tight. Unlike an OTF or direct sensor based system that measures the actual flash.

 

So far, Nikon's i-TTL pre-flash system hasn't impressed me, and I was hoping for something better in an MLC. After all, there's no need to hide the metering system in a pentaprism and blind it for the duration of the exposure.

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The Sony has several flash modes, and I've only used the "Fill Flash" option. I've also used studio flash units with flash and camera in manual mode (hand held meter), and a radio trigger. There's no delay in that case. The maximum shutter speed is 1/250, but with studio flash (long duration), it's often best to use 1/125 for even response across the frame.

 

Don't give up on Sony just yet. There are a lot of flash options in the flash and camera menus, and I've barely covered the basics. The "Fill Flash" mode works well with relatively static subjects. I set -1 stop compensation on the flash itself for wedding and group shots, which gives good modeling. You can also set flash comp independently in the menu. To catch a toddler mid-flight jumping from couch to foot rest - fogeddaboutit.

 

I just took delivery on an A9, and so far it's way beyond anything previous models can do, speed wise. I'm still skimming the manual for basics. Haven't tried it with flash yet.

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I think iTTL is something dreamed up by marketeers to catch the eye of amateurs. TTL is okay for on-camera flash, but if I have time to set up stands, multiple flash units, etc., I have time to set ratios and exposures using a flash meter. It takes less than one minute to adjust the lights and nail the exposure if you're using a familiar setup, and it doesn't change between subjects unless you move the lights. Edited by Ed_Ingold
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Fuji pre-flashes. (Tested shooting into a flash on optical slave with system flash on X-E1 in TTL & manual mode.)

I think I read all current Leicas are pre-flashing too? - I own no system flash for mine.

Out of curiosity, since I have a 2nd Yongnuo for EOS + wireless controller under way: What kind of setup do you all recommend to convince folks of the flaws of pre-flashing TTL?

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I can't speak for all mirrorless cameras, but the Sony A7/A9 use a "flakey" pre-flash, and only with the mechanical "rear" chutter. It's highly effective, arguably more accurate than my Nikon SB=900 with a D3. There is also the option of using a sensor in the flash for auto exposure, but the Sony still requires a mechanical shutter.

 

The electronic first shutter can be used. I think the mechanical shutter "clears" the sensor after the pre-flash is read, then the exposure and a second shutter. There is a lot of lag using an A7Rii. The A9 is supposed to be faster, but I haven't tested it yet.

Yeah on both the Panasonic GX7 and Fuji X-Pro2 models I've used, flash only works with the mechanical shutter. Won't fire if on ES. Or I haven't gone deep enough into the flash functions to change that.

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I was mistaken about the double shutter action with flash in a Sony A7Rii. I use the e-shutter mode most of the time, unless I need totally silent operation. The front shutter is electronic and the rear shutter is mechanical (front/rear relative to the exposure). I think I was mistaking the pop of the flash for a mechanical shutter. Since there are no separate flash sensors in the camera, the pre-flash must be measured by the sensor itself. The A9 does the same thing, only twice (or more) as quickly. It's possible that the metering mode (matrix/center/spot) applies to the flash, but there is no documentation to that effect. At any rate, TTL flash exposure is very accurate.

 

The flash will not fire if the silent (totally electronic) shutter is selected. This is a menu (or programmed button) operation in the A7Rii, and an automatic selection in the A9. Flash works in the "normal" double shutter mode too. You would use the non e-shutter option to avoid certain artifacts, like the "rolling shutter" effect. The flash is nearly as loud as the mechanical shutter.

Edited by Ed_Ingold
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I just took an oscilloscope trace of what happens with Nikon's i-TTL sequence. I was surprised to see there are actually two pre-flash pulses - goodness knows why.

 

The first pulse lasts approximately 200 us (millionths of a second) and appears to be of variable duration. The second pulse is even shorter and serves no purpose that I can conceive of. Then there's an eternity wait of over 70 milliseconds before the exposure flash - far more than long enough to allow the mirror to lift I would have thought.

 

Now 200us is an incredibly short time for the camera to get a decent meter reading. Maybe it varies because the camera signals "got it" back to the flash to quench the pre-flash. Who knows?

 

The 70 milliseconds delay would allow for Nikon's AWL "morse code" exchange between master and slave flashes. I can't think why it should be so long otherwise.

 

One implication of this is that with their current i-TTL protocol, no Nikon DSLR can ever fire at over 11 FPS.

 

The second implication is that i-TTL wastes about 10% of the available flash energy on pre-flashes. More if AWL is used.

 

Third implication is that there's at least an 80 millisecond delay between pressing the button and the shutter opening. More than most MLCs that get slated for their shutter delay.

 

Those aren't compelling reasons alone to condemn i-TTL, but they don't point to an elegant and efficient protocol.

 

FWIW. Silent mode is meant to make firing the camera inconspicuous. So no surprise that the flash is suppressed.

Edited by rodeo_joe|1
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"Silent mode", whatever it means prevented my X-E1 from firing flash too.

With Sony, silent means the shutter is completely electronic, front and rear exposure. The only sound you hear is the lens focusing and diaphragm closing. In the A9, which is designed around silent running, you can add a shutter sound played through a tiny speaker. It also marks button presses, focus lock and mode changes if you are so inclined (is there an emoji gagging on a spoon). A shutter sound, real or emulated, is reassuring to groups and subjects at events. Concerts not! I was once asked of the sound of my Hasselblad could be turned off. That camera never attended another concert. (It was the conductor asking, over 60 feet away while I was shooting.)

 

Even with pre-flash, modern units don't necessarily need much power.Using the flash in fill mode (Sony M60), a set of four AA batteries last weeks or months. I just changed them for a wedding, since the last set had been in place since early April.

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  • 2 weeks later...

You know, you don't really need a TTL flash with a digital camera. TTL might speed things up somewhat but that's about it. Look, with any camera that has the capability to show you an image you just captured, you can use any flash with variable output -- or a thyristor for that matter. With a variable output flash set to manual mode, you just dial in the amount of flash you need for the task at hand. If the flash has a thyristor circuit, even better -- let the flash do the work. It'll shut down automatically once correct exposure has been reached.

 

I have a Sony NEX 7, which has that weird flash shoe that Minolta dreamed up for its Maxxum cameras. What were they thinking?!. I bought an adapter from Amazon for it -- made in China, but it works.. Anyway, my adapter slides right into place. It has a large dot where the main flash connection occurs, and four outlying dots, grouped in a rectangle below the large central dot. The arrangement looks like the pattern Canon uses for its TTL flashes, but I dunno, there might be some very slight differences in placement of the dots. Real world, though -- I have a couple of TTL Canon flashes and a couple of TTL Nikon flashes, all of which I can control the output, plus they all also have just a plain, old-style non-TTL auto mode. What I have done with all of them is set them to Manual mode, dial in the correct power level and then fire away. I can typically leave it in a given setting until the light changes in a significant way. In which case, all it takes is a couple of test fires to dial in the new setting. Of course, if I'm using a flash in its "Auto" mode, I don't even have to worry about adjustments as long as I stay within the "Auto" mode's working range.

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The flash shoe is completely dead in a Sony A7xx or A9 unless a mechanical shutter option is selected, There is an auxiliary PC jack on the A9, which is also dead. Either port can be used with a non-Sony flash in manual or auto mode (which uses a sensor in the flash body to control exposure). I have a Sony HVL-F60M flash, which is arguably the most accurate TTL flash I have ever used, including a Nikon SB900 on a D3.

 

I'm not much for remote multiple or TTL flash. IMO, it's just too fiddly and inconsistent compared to manual flash set up using a flash meter. On-camera is another matter, and an accurate flash saves a lot of time. I usually use Fill mode, -1 stop, with the flash diffuser in place.

 

AFIK, all variable flash units use a thyristors to trigger and quench the flash. That's how a low voltage contact can handle a 600 VDC discharge. Thyrotron tubes went out a long time ago (I have a couple of those flashes too).

Edited by Ed_Ingold
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