When you use more than one flash, you can adjust each light individually. If you use speedlights and your camera maker’s wireless TTL functionality, you can do that in two ways:
Canon: relative, using ratios. As in “A:B = 4:1” meaning A is 4x (two stops) lighter than B
Nikon: absolute, by adjusting individually. E.g. “A = No adjustment; B = -2 stops adjustment”.
An example of this using two Canon flashes.
Ratio between key light (face) and background light: 1:2
2:1 (you are getting the hand signals by now I presume):
The preference is yours: mine is 2:1. But that is largely a matter of taste.
If you use manual flash and radio triggers, it is conceptually easier, since you set up each flash by itself, independent of other flashes. Ratios are a little bit trickier to get your head around, because it is not immediately clear which flash will get darker and which flash lighter, and to what extent. So trial and error will be required. Either way, key point is that you should think carefully about how bright each flash is, in a multi-flash setup.
Today, a quick but important (and as far as I can tell, pretty unique) TTL flash tip.
So you want to know if you can do a certain shot? TTL outdoors is fighting against the sun. Do you have enough power to do the shot? It’s always a battle.
You can of course fire a test shot. If the flashed area is dark, try exposure compensation, maybe. Or spot metering, or using FEL (flash lock). Or rely on the LCD display on your flash to tell you the expected distance. All very time consuming and uncertain. What if I just want to know “do I have enough power in my flash to do this shot” and then if yes, figure it out from there?
I am glad you asked.
Set your camera to highlight review mode (“blinkies” on)
Set your flash to MANUAL
Set power on the flash to FULL (100%, a.k.a. 1/1)
Take the shot!
Now you know:
Blinkies means yes, you have enough power. Turn the flash back to TTL and go from there.
No blinkies means that however you compensate or meter, nothing you can do. Get closer, or increase your ISO, and try again.
Simple, innit? This trick has saved me countless times.
You know (if only because I have discussed it before) that you can set your flash to manual or TTL. I thought I would revisit this, and show you some shots I took Wednesday.
Manual means you set the power level; TTL means the camera fires a preflash and measures the return, and then sets the power level based on that. TTL (Nikon calls its version i-TTL, Canon calls its version e-TTL) is the default setting (the panel on the back of your flash says something like “TTL”).
Unlike David Hobby, I tend to use TTL most of the time, not manual.
TTL is a major revolution in camera technology, because it allows you to shoot varying scenes without having to worry about distance. In particular, you can bounce anywhere you like, off a different wall for every shot, and you can use whatever modifiers you like, and not worry about measuring. And you can use “fast flash” to exceed the camera’s flash sync speed – useful on sunny days.
A sample, shot with TTL on Wednesday:
Indeed as David points out, TTL has drawbacks: the major one being that it’s not perfect. Its measuring is finicky. If you always aimed your viewfinder at an 18% grey surface you would be fine, but the meter is in evaluative mode, and on top of that it has an undocumented bias toward the focus point. All that means that if I focus on a black area I get grey (too bright), and if I focus on a white area I also get grey (too dark). So I need to use flash exposure compensation. And check the back of the display frequently.
TTL’s pluses, then, are:
You can use it anywhere, any time.
You do not need to meter or set anything.
You can do it when the subject varies.
You can bounce off varying surfaces, like when you shoot an event and both you and the subjects are constantly moving around.
You can exceed your camera’s flash sync speed by using “fast flash” (“auto FP flash”in Nikon terms)
You can use any modifiers you like
And its minuses:
It can be infuriatingly inconsistent.
Your subject’s brightness makes a difference.
Reflections can spoil a picture by underexposing it.
You’ll need to do more post-production work, as in a fast-moving event, where the setup changes with each shot, quite a few images will be half a stop under or over.
You’ll even miss a few images.
So TTL is great when things are predictable, but it is also very useful when things are not predictable (like when you, and they, move).
Now let’s move to manual flash. Manual is the opposite to TTL: it is utterly predictable and consistent but you need to do all the work, and it is totally useless when you and the subject move.
So I use manual when:
I want consistency, and I can ensure that nothing moves (like in studio portraits).
I have time to meter.
The flash is just adding light, like an accent, or like fill on a sunny day, when the exact power level is not that important (if the flash were a bit under or over it would not make a material difference to the image)
I am using Pocketwizards, e.g. for outdoors shots – which will therefore need to be predictable.
Don’t get me wrong, I love the predictability of manual flash firing, not to mention the predictability of the use of Pocketwizards.
So in fact I shoot manual flash if possible, and if not, then TTL.
Do I sound like I am contradicting myself? No. Because I shoot events. And events mean I need to be on my feet in a constantly changing environment. And that is when TTL shines (pun intended). Every shot I am in a different room, and I bounce off different surfaces. So that is why I usually use TTL.
And when using TTL, it is all about knowing how it is going to react, and being able to solve the problems. That is what I teach in my courses (e.g. at Henrys School of Imaging, and in the all-day course coming up on 30 May, and in Las Vegas on July 12+13, and many more times in between). There’s a lot of problem solving, involving tools like:
Flash lock (FEL/FVL)
Knowing exactly what it will do
Remember, while a setup shot has to be right, in a fast-moving event, the objective is to get within half a stop to a stop, as long as you shoot RAW. And believe me, this is eminently doable.
Another sample from Wednesday, where bright ambient light necessitated 1/400th second, which meant using Fast Flash:
Snacks, also from Wednesday:
Do try to bounce, and use you camera on manual settings (flash is still measured). The following may work, but only if you are lucky:
I would like to see her shots, but I know they would be better if she used an external flash and bounced it off the ceiling behind her!
So why would you use flash outdoors during the day?
Sometimes it is obvious: to fill in shadows on backlit subjects. Or to soften hard shadows. But sometimes you do it for more artistic reasons.
Let me illustrate this with a shot taken during the Get Out and Shoot run we did in Toronto early this week – the workshop I wrote recently.
Imagine you are shooting someone – me, say – on a bright day, but in a spot where I am in the shade against the shady side of a grey building. Before you know it you get a dull picture: grey and low-contrast on all counts: blaah.
So that’s when you bring out the flashes. Say, two remote “slave” flashes, fired by a “master” flash on the camera. One slave to the camera’s left, shining into a Honl reflector, and aimed at the subject’s face, to add bright light to the subject. The second flash is equipped with a Honl Speedstrap and on it, a green gel, and this flash is aimed at the grey wall behind the subject to make it less grey.
Now you get this:
You will agree, I hope, that this is a lot better than it would have been without the help of flash. Even, no, especially, on this bright day.