Adventures in Photography: Shutter Speed, Aperture, ISO, and Flash

Taking portraits outdoors is easily the most challenging task I've tried thus far. With a little understanding of how our camera works it was possible and for my first attempt, focusing solely on exposure, I think I got some decent results. 

Before we move on it's important to know how our camera takes pictures and what changing settings will do. They say if you want something done right you should do it yourself. Getting your camera into manual mode will give you that level of control instead of letting your camera guess and probably fail at what you want. Mark Wallace does a great job explaining the exposure triangle in the first video of  this series on exposure, so make sure you watch that. In the meantime here's my gross over simplification.

There are three ways to make our pictures brighter and darker. ISO, shutter speed, and aperture. Adjusting each of them will have an additional effect on your photo other than just the picture's brightness.

ISO is our camera's overall sensitivity to light. The higher the number, the brighter your picture will be. The thing to keep in mind with ISO is noise. Some cameras can handle this better than others but essentially, the higher your ISO, the more noise you get. It's a lot like distortion on a stereo. If you crank it up too loud, even when nothing is playing, you'll hear a hum. Ideally you want to keep ISO as low as possible, but in our stereo example, if it's too low you won't be able to "hear" anything at all. Cameras are getting good at shooting with high ISO and editing in post can help too, don't be afraid to crank it up to get your shot. Of course, the better you do in camera, the less you'll have to fix later. Our boy Mark explains further here.

Aperture is a hole in your lens that can be adjusted to let more or less light in. The other thing this effects is depth of field. The smaller the number, the larger the hole and the less range of things that will be in focus. Depending on a few factors your depth of field could be so shallow that your subject's nose will be in focus but their eye won't. Mark explains better here.

Shutter speed is how long your camera lets light affect the exposure. The longer it's open the brighter the picture. The effect of shutter speed, for the most part, is blur. If your shutter is open long enough it will record anything that moves, even your hand movement. A fast shutter speed will freeze motion. Get it fast enough and you can stop a helicopter blade. When you bring a flash into the equation you have another thing to consider. Flash sync speed. Depending on your camera this could range quite a bit but most newer cameras are around 200th of a second. My t3i is 200th of a second. A good way to think of this is that your camera's shutter is starting to close while the flash is still on. That isn't exactly how it works but it's the easiest way to explain it without a bunch of technical diagrams of shutter mechanics. Mark talks about shutter speed here.

This is what happens when you go over a camera's sync speed

1/400th sec

The flash is still putting out light by the time the shutter starts to close resulting in a big black bar in our photo. There are flashes that have what's called High Speed Sync. When a camera's shutter speed is at or lower than the flash sync speed, there is a moment where the sensor is completely uncovered. When it goes above it's flash sync speed, the hole in the shutter is narrow and it scans across the sensor meaning that only part of the sensor is able to receive light at any given moment. With my flashes, they only have the ability to output one light burst. High speed sync flashes will put out several bursts of light when in that mode so there is flash for every part of the sensor when it's uncovered. This becomes important in really bright situations like the one I was in with my model.
Mark helps out on high speed sync here.

Lets say we want an extremely shallow depth of field. We want our subject in focus but everything behind her as blurry as we can get it because it's some ugly parking lot or something. So, we'll crank our aperture to the lowest number it can go which gives us a big hole and a lot of room for light to come through. There will be situations where even at your camera's lowest ISO it's still going to be too bright. We know from the exposure triangle to get shallow depth of field at these settings we're going to need to have a short shutter speed to limit the amount of light that comes in. It might be so bright that the only way to get a proper exposure based on these settings is to go over the flash sync speed. You might be thinking, if it's that bright, why the hell am I using flash? We'll get to that in a moment. Now your options are compromise on your aperture, make it smaller and bring back some focus into your ugly background, buy a flash that can do High Speed Sync, or the method I have chosen, use an ND filter. Basically, sunglasses for your camera.

Now we can get into why we're using a flash when it's this bright.

f/8 1/200 iso 100

In this photo I'm not using any flash. The Sun is bright as shit and her face is still dark. You can see in the upper left corner that my sky is already blown out. I could adjust my settings to make her face brighter but I'll probably start to lose detail in her hair and that sky is definitely done for. Now if we want detail in the sky we have to adjust our camera to make it darker, but our subject's face is already dark. In comes our flash!

f/8 1/200 iso 100

Here is a photo with the same settings but I added a flash. We still have the nice hair light from the Sun and now there's some light on her face. If I had the sky in this photo, however, it would be way blown out. This article by Neil van Niekerk does a great job of explaining what I'm talking about.

In it he talks about how the ambient exposure and flash exposure are two separate things and that gives us the opportunity to do some cool stuff.

In this situation, to get detail in the sky I had to put the ND filter on to eat up enough light to keep my shutter speed down. Adding the the flash added light back on my subject and bang! We have a pretty cool exposure and that's all I was worried about on this shoot.

These photos have plenty of room for improvement, but the point of them was to learn and learn I did. Next time I try this I can get to where I want much faster which leaves more time to make them better. Maybe next time I'll be able to prevent houses growing out of her head and keep my softbox out of the frame.

If this isn't making sense, don't worry. Go read and watch as much as you can, go practice, and come back and read and watch everything again. I'm no expert, but I probably had a question you have right now and might be able to help. Leave me a comment! Next time is the big day!