Real world lighting: Flash and Ambient Mix

Now we’re going to get a bit clever – we’re going to try mixing different light sources. We’re outside on a freezing cold day where we have ambient light – the daylight – although not much of it as it’s so overcast, and we have a flash head with a softbox, and a 2nd flash head with a reflector. Now, we can shoot with one light or the other – we could shoot with just ambient, or just flash, or we can combine the two to create something a bit more dramatic.

So, let’s start by looking at our setup.

Ambient and flash mix setup

The general outline is pretty familiar to us now – we’ve got a softbox on the front of a battery powered flash head in front of and to Lisa’s left, and then behind her on her right, we’ve got another battery powered flash head with a zoom reflector on, aiming back at her. The camera is on a tripod, with a radio trigger attached, and of course, we’re outside in (pretty grotty) daylight, rather than in the studio. As a quick note, I’m using the battery flash heads in this instance as of course, they don’t need to be plugged in, and I can move them round outside with ease.

Now, we’ve touched on the concept of mixing light sources before – remember we shot that globe on the table, and by varying the shutter speed we were able to affect how light or dark the rest of the shot was, whilst keeping the globe consistent. The same sort of things will be at work here, but I want to finesse them a little, and add a couple of new elements.

Here’s an image with no flash on, straight out of the camera. The exposure is 1/15s, f2.8 at ISO 100.

Ambient light only
Ambient light only, 1/15s shutter speed

It looks fine, if a little flat. Lisa’s eyes are a little dark, and the only thing separating her from the environment is the depth of field.

Now, let’s turn our flashes on. To keep things simple, I’m not going to detail exactly what power these flashes are on, nor change them from shot to shot – they’re simply set to give me a correct exposure at f2.8 – remember flash exposure isn’t affected by shutter speed until we go faster than the maximum sync speed. Immediately we can see that adding the flash has lifted the shadows in Lisa’s face, but not had any effect on the buildings and alley behind.

Flash added to ambient portrait
1/15 second shutter speed

Now, let’s adjust the shutter speed, which will only affect the parts of the image lit by the ambient light. First, let’s speed up by one stop to 1/30s. 

1/30 second shutter speed
1/30 second shutter speed

Lisa’s still looking good, and the rest of the shot is starting to look darker. Now, another stop, down to 1/60s. 

1/60s shutter speed
1/60 second shutter speed

Lisa is still well lit (although she looks subtly darker) but the rest of the scene now looks as if night has fallen. Go another stop to 1/125s

1/125 shutter speed
1/125 second shutter speed

and even further to 1/250s 

1/250s shutter speed
1/250 second shutter speed

and the effect becomes even more marked. If we go past 1/250s we’ll start to see black bands across the frame as you can see here with the shutter speed at 1/500s –

1/500 second shutter speed

We’ve now exceeded the maximum synchronisation speed of the flash, and since I’ve not turned on the clever high speed sync mode in these Profoto flashes, that’s as far as we can take it. I just want to stress that as I’ve altered the shutter speed I haven’t adjusted the flash power at all – it’s stayed the same each time.

Remember – the pulse of a flash is so brief that the length of time the shutter is open for has almost no effect on it, so in a scene like this where there are areas lit by flash, and by ambient, continuous light, you can effectively have 2 different exposures – an ambient and a flash – and adjust them as you choose to create the effect you want.

Now, I want to delve a little deeper, and examine why Lisa got a little darker when we made the shutter speed faster, despite her being lit by the flash. In a scene like this, even though we think the ambient and the flash as being 2 distinct things, and we can control them separately, the fact is Lisa is lit by both, to some extent. That ambient light is always present until you under expose it so much that only the flash is having any effect. This is why as we speed the shutter speed up, the light on Lisa’s face changes as she becomes more and more dependent on the flash to light her. The main thing the ambient light is doing is lifting the shadows. You must bear this in mind when mixing light sources – think carefully about which light is doing what, and don’t be afraid to check the back of the camera and fine tune things as you go along. In this shot, if I wanted a really dark, moody shot, but still wanted to keep a bit more light on Lisa’s face, it would probably help to add a reflector to lift those shadows that start to appear as the shutter speeds up.

Using flash in a situation like this gives us yet another chance to explore inverse square law – although I expect you’re sick of it by now. Let’s switch from the initial ambient only shot,

Ambient only
Ambient only 1/15s shutter speed

to the darkest of the lot at 1/250s. 

1/250s shutter speed + flash
1/250s + flash

Watch how not only do the ambient parts of the image darken down, but Lisa seems to be almost “cut out” against the environment. This is clearly a by-product of inverse square law – if we expose correctly for Lisa, there’s no way the light from the softbox near the camera will be able to expose the walls of a building 100 feet behind her. Now, in one obvious sense, this is the entire point – we’re trying to focus attention on her, and create drama – but you can easily take this too far. A shot like this can quickly become just a body on a very dark background, and that might be your intention, but it usually makes sense to keep some of the environment visible! You also need to be aware what your lights are capable of. We were quite lucky that the day we shot on was overcast – that meant the flashes didn’t have to work very hard to overpower the amount of daylight. On a bright sunny day they would have worked harder – the addition of a softbox might have knocked too much power out of that front light for example, and I wouldn’t be able to achieve this darkening down effect without changing the modifier to something else. As with everything else we’ve covered, all the four characteristics of light interact and play out on the image we’re trying to create. I’m afraid there’s no escaping them, but now you know so much about them, you can approach a shot like this with a great deal of confidence.

One last detail – Flare. Look at the left hand side of the frame, and there’s a distinctly bright area.

Flash + 1/30s shutter speed
Flash, 1/30 second shutter speed

Now, I left it in as an example. Strictly speaking it shouldn’t be there, but I quite like it, and it’s a good excuse to talk about it. I mentioned flare briefly when putting a shot together piece by piece, but it’s worth going into a bit more detail. The definition of flare is “non image forming light” and is caused by light looking straight into the lens – backlighting, as we’ve encountered a few times. Usually it will reduce the contrast in a shot, and taken to extremes, it’ll be pretty much all you see. A little dab of it here and there can be quite effective though – just use it sparingly. Backlighting in this way will also show up anything in the air between the light and the camera, so if you’re trying to make dust, rain, smoke or powder look dramatic, you will want to backlight it in some way. Look closely at the flare area in this shot, and you’ll see fine drops of rain because not only was it freezing, but also drizzling too. She’s a real pro that Lisa! 

Flare on edge of image
Flare on edge of image

To fine tune flare, you simply need to carefully control the angle, and fall of light from any lights that are pointing towards the camera. In this instance our backlight has a zoom reflector on, and it’s zoomed in pretty tight to keep the spill of light down, to reduce the flare further I could angle it away from the camera and more onto Lisa, add a modifier like a grid, or place a flag somewhere between the light and the camera. You can also control it to some extent by altering the quantity of light – if I turned the power of this light down, you’d see less flare, although you’d also see less light on Lisa.

An important question to ask is “Why bother doing all this? There’s already light outside, so why complicate things by bringing flashes in?” Well look at the difference between the original, daylight only shot, and the finished flash shot.

Before and after adding flash and tuning the shutter speed
Before and after adding flash and tuning the shutter speed

I think you’ll agree the shot with flash has distinctly more impact doesn’t it? It also focuses our attention much more on Lisa, rather than being a photograph of Lisa and a back alley! The first shot is just fine, and would suit some applications, but the lit version is definitely more interesting, and more people are likely to look at it. That, really is the secret of why we learn how to light – so we can employ all these various tools, techniques and equipment to create images that make us happy and excited, and that people want to look at.

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