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How to Balance Flash and Ambient Light in Portrait Photos

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Read Time: 11 min

Welcome back to 'Introduction to Flash Photography'. In this lesson, you're going to learn how to balance the ambient light in your photos with the light from the flash that you're going to be adding to the photos. You will learn about the differences between using TTL mode on your flash, and manual mode, and you'll also learn what a sync speed is and how it affects your images.

Auto and Manual Flash Modes

Let's get started with TTL versus manual mode on your flash. For the rest of our lessons, we're going to be using flashes that are not built into your camera, and that allow us to manually control the power output of the flash unit.

If the flash you have also has TTL built into it, that's great, but it won't really be necessary for most of what we're going to be doing. Basically, TTL is just like putting your camera into auto mode, except now we're going to be putting our flash into auto mode. Your camera and your flash will put their electronic brains together and they'll try to figure out how to best expose your image with the added flash. Now sometimes it works brilliantly, especially if you're in a situation like a wedding where you don't have time to set up, but mostly it gives us less than stellar results.

As you can probably tell, I'm not a huge fan of auto mode on your cameras, and that applies also to TTL and auto mode on your flash. I'm especially not a fan of TTL on your flash when you're learning to use flash. The main reason being when you use manual flash you can look at the back of your flash and see what power you're using. Knowing what your power setting is is one of the most important pieces of information that you'll need as you learn what does and does not work in flash photography.

When you use TTL, you have no idea what power settings were used, and it becomes a very difficult game of guessing what your camera and flash decided to do. How can you learn when you don't really know what's going on and what settings are being used?

The one time that I use TTL over manual flash is when my subject is quickly moving closer and further away from my flash — like when I'm shooting the dancing during a wedding reception. Since my subject is moving so quickly in and out of the range of my flash, I don't have time to adjust my flash manually for each shot. While TTL is not quite as good as the results I get from manual control, it's very quick and it makes adjustments quick enough to keep up with the action. Other than that, I pretty much just keep my flash on manual mode.

Sync Speed

There's one final thing we want to understand before we move on to balancing flash and ambient light, and that is the flash sync speed. Now most DSLRs have a maximum flash sync speed of about 1/200th to 1/300th of a second. If you're using a flash and you use a faster shutter speed than your camera's maximum sync speed, you'll end up with dark bars in your photos.

On many units, when you turn your flash on, it'll automatically lock the camera's maximum shutter speed to the maximum sync speed. Most of the time, this is not a problem, but sometimes it requires some creativity to figure out how to get your shutter speed slowed down to your sync speed. And the exception to this rule is with some higher end flashes that have what's called high-speed sync, or HSS.

High-speed sync allows you to use a much higher shutter speed along with your flash, but it comes at a cost. That cost is that the maximum power of your flash is reduced dramatically. So, if you need a lot of flash power, high speed sync might not be the best option for you.

All right, now that we have all of that taken care of let's move on to how to balance flash and ambient light in your images.

How to Balance Flash and Ambient Light

First let's define ambient light. In my mind, ambient light is the natural light in your scene, and I generally think of it as light that I have little to no control over, or that is impractical to change. When you're shooting outdoors during the day, your main source of ambient light is the sun. Whether it's the direct sun shining on your subject or the scattering of sunlight caused by the sky in a shot in the open shade. Or sun bouncing off of any manner of things like buildings, sidewalks, or clouds.

When you're photographing at night, your ambient light will come from street lights, or cars, or twinkle lights, or pretty much anything that is putting out light. When you're inside, ambient light typically comes from the lights built into the interior space, like overhead lights and lamps. It also comes from the sun when it's filtering through the window, so you get a little bit of outdoor light mixed with your indoor light, but all of its ambient light.

Since most of these situations make it impractical or even impossible to change the light in our scene, we must use what we learned in the lesson about exposure to adjust our camera to the lighting conditions around us. Now most of the time this works pretty great, and you can get acceptable results by trying different angles and positions or by tweaking images in post-production. But take a look at this situation:

The difference between the brightest parts and the darkest parts of the scene are so great that our camera cannot render all of the detail in the highlights and in the shadows. And so we have a decision to make. Do we want to silhouette our subject with the sky behind him exposed properly? Or, do we want to expose our subject properly, and lose all of that beautiful detail and colour in the sky to highlights?

Or — there's a third option. You can learn how to balance flash and ambient light, and you can get the best of both worlds.

In a situation like this, my thought process is to figure out what I can and cannot control in my scene. For this frame it should be obvious that that I lack the ability to move the sun or control the brightness of the sun since it's really too far away from me to reach and really too big for me to move. My subject on the other hand is much smaller, much closer and much easier to move.

So since I can't really control my background light physically, I'll use my camera settings to get a proper exposure of the light that's there, and this is what I end up with.

Just like earlier, a beautiful background and a silhouetted subject lost to the shadows — until I turn my flash on. So if you were a professional photographer with a dedicated light meter and years of experience, you would probably be able to dial in the right flash setting on your very first try — and get a beautiful image. But I'm guessing you're not a professional photographer and you probably don't have a light meter. And you probably have no idea where to even start when it comes to what your flash setting should be.

Well that's okay because you're learning, and I think the best way to learn is to play. So when you're trying this out later, I just want you to keep this in mind, and don't be afraid to take bad photos. I know I've learned a ton more about photography from my bad photos than I have from my good photos.

So for now, we're just going to start playing and we're going to start out a 1/16th power. The reason I choose 1/16th is cause it's pretty much right in the middle of my power range, and I don't want to use full power right off the bat because it just kind of wastes batteries and it's really bright and sometimes it blinds your subject. There's no reason to do that.

1/16th Flash Power

In my example, one 16th of a power was not quite enough, so I'm going to turn it up just a little bit. So let's try a 1/2 power and see what that looks like.

1/2 Flash Power

Whoa, that's way too bright. Luckily I'm a digital photographer and I can see immediately how my adjustments are affecting my images. And as I'm shooting I'm learning. After a couple of test shots, it looks like 1/8th power is my sweet spot and it gives me an image that we can use.

1/8 Flash Power

Now looking at this image, it's great to see that we can get the beautiful colour and the details that are in the sky. And now by adding the flash to it, we can also see our subject. and we get the best of both worlds. This is where flash is actually really great.

So let's try another common lighting situation and I'll show you how I would balance the flash and ambient light in this scene.

Here, we're going to be looking at a night scene. In this scene, our ambient light is all of the lights that are in the background; the neon lights, the flickering lights, the street lights, the car lights. Now, I have made the creative decision to place my subject in this position because I like the composition.

As it turns out, there's not really enough ambient light to light my subject fully, and so we can't really see her and she's lost in the shadows. So let's see what happens when we adjust our camera settings to expose our subject correctly.

Wow, that's not pretty at all. All of the colour of the lights is gone, the drama of the nighttime has disappeared, and the image is flat and boring. We've also added another problem — motion blur from camera shake.

I didn't bring my tripod and the super slow shutter speed that was required to properly expose my subject was just too slow to get a sharp image. So when I took the picture, my camera moved just a little bit and while the shutter was open, the whole scene would shift on my sensor. That's what gives us these blurry lines and just this out of focus, soft photo.

So let's see what we can do to make this image better by balancing flash and ambient light.

First, we want to raise the shutter speed to a point that will eliminate the motion blur from camera shake and bring back the drama of the nighttime scene. Then we're going to turn on our flash and see what it gives us.

My experience has taught me that based on my camera settings, the lighting, and the distance of my subject from the flash, I'm going to want a flash setting of about probably 1/64th power.

And what do you know? That's actually pretty close to just what I wanted. I think I'd like it to be just a little bit brighter, so we can turn the flash up just a tiny bit, and take another shot.

And that's perfect. And now since all of my settings are locked in, in manual mode, I can just click away and forget all about the settings of my camera. This frees me up to interact with my subject and to get the best out of them, and it also allows me to concentrate on composition so that I can get images that are visually pleasing and that they fit the frame just right.

Ultimately, this gives me the exact images that I usually want.

Now that you have a general understanding of how to balance ambient light, I'm going to give you a homework assignment. Don't worry, this is going to be a fun homework assignment. I want you to grab a friend and head out to a place with some interesting lights, and I want you to try to make some images similar to the one that we just made in the second example.

The most important thing I want you to do is to play and have fun doing this, and don't delete any of the photos that you take on your card as you're shooting. Bring home all of the photos that you take and so that you can look through them.  Then you can go through each photo and analyze what went right, and what went wrong in each photo. This is the way that I learned, and this is the way that you're going to get creative at lighting.

So get out there and have some fun doing your homework. When you get back here, you'll be ready for our next lesson, which is all about the different kinds of speed lights that are available to you, and which one will suit your needs better as you move forward.

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