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Manual Exposure: How to Use Aperture, Shutter, and ISO to Make a Studio Photo

Welcome back to our Introduction to Flash Photography series.

Before we launch into talking about flash, let's make sure we're all on the same page when it comes to exposure. All of our instructions about studio photography in this series are based on the understanding that your camera will be in manual mode, where you have complete control over your camera and the three settings that we're about to learn about.

If this scares you, don't worry, it's actually much easier than it seems. In fact, I believe it's much easier to learn photography in manual mode, and by the end of this lesson, I think you'll feel much more confident with manual photography. Understanding how to control your exposure without a flash is the first step in getting great images with a flash.

What Controls a Photographic Exposure?

Exposure is really nothing more than how much light reaches your sensor or film. We have two settings that allow us to control how much light reaches our sensor and one that controls how that sensor reacts to light. These are:

  • shutter speed, or how long the exposure lasts
  • aperture, the size of the opening in the camera
  • ISO, the sensitivity of the film or sensor

Shutter Speed

Shutter Speed is the measurement of how long the shutter in your camera stays open during an exposure, allowing the camera's sensor to be exposed to the light of your scene. Typically shutter speed is expressed as a fraction of a second.

On my camera '30' means 1/30th of a second and '8000' is 1/8000th of a second. For shutter speeds that are over a second, my camera displays them like this:

The number on the left of the quote marks is the number of the whole seconds, and the number on the right is tenths of a second. So this would be 1.3 seconds.

This would be 30 seconds:

When it comes to exposure, the longer your shutter is open, the more light gets into your sensor and the brighter your final images.

Aperture

The Aperture is a measurement of the size of the opening in your lens. I think the best way to explain this is to show you how it works. Here is an older lens that has a manual aperture that allows us to control the aperture by turning a ring.

As you can see when I rotate this ring, a group of blades rotate in and out and they make the hole that the light is coming through bigger and smaller.

On newer lenses the same thing is happening, but instead of turning a ring, we adjust the aperture in the camera with the buttons. When we press the shutter button, just before the shutter opens, the camera electronically tells the lens to close its aperture to the one that you selected in the camera. You can see that at work here:

Every time I hit the shutter button the aperture closes down just before the shutter opens and then opens back up right after the shutter closes.

f  Numbers and Controlling Exposure

Aperture is expressed as an f number. An f number represents the relationship between the size of the aperture and the focal length of the lens being used. A small f  number means a larger aperture and then a large f number means a smaller aperture. For each step between f numbers, the amount of light changes, and although we can calculate this for a lens given the characteristics, most manufactures helpfully mark their lenses with helpful f-stops at the right places.

Picking a smaller f number means opening to a larger aperture, which lets more light into your camera, and thus creates a brighter image. Picking a higher f  number narrows the lens down to a smaller aperture, which lets less light into your camera and that creates a darker image. Most lenses have aperture values that range from around f/1.2 up to around f/22, and that's quite a big difference. 

Here is a useful thing to remember when using the f-stops marked on your lens: Opening the aperture by one full f-stop doubles the exposure to light, closing the aperture by one full f-stop halves the exposure.

Sensitivity

The final camera setting that I want to talk about is ISO. ISO is a measure of how sensitive your sensor is to the light that's coming into the camera. With film cameras you can use different films with varying levels of sensitivity. In digital cameras all you have to do is turn a dial.

ISO values are expressed as numbers that typically range from around ISO 100, on the low side, to around ISO 1600, or even more, on the high side. In fact, some of the newest high-end DSLRs are capable of ISO ratings of up to 409,600, which is an amazing feat of modern engineering. A few new dual-ISO cameras allow extra low-light performance.

When you take a photo, your digital sensor takes the light that the aperture and shutter have allowed in, and it converts that light energy into an electrical signal that your camera records. When you change your ISO from around 100, to say 400, you're telling your camera to amplify the signal just the way a stereo amplifies an audio signal. The sensitivity of your digital sensor is fixed, but the software used to amplifying a low signal without noise and distortion (or compensating for it) has improved significantly, both in the cameras an in post-production.

Raising the ISO means turning up the volume on your digital sensor; the higher your ISO number goes the more your signal is amplified, meaning as your ISO number goes up, you're also brightening the image.

Balancing the Exposure Triangle

Let's bring this all together and let's see how to get proper exposure using manual control of all three of these settings. I'll do this using the light meter that's built into my camera. I usually set my light meter to spot meter so that I can make sure that I'm getting a proper reading for a very specific part of my photo. Since I photograph people, I generally meter for the face of my subject.

For today's lesson, we'll be using this vintage flashlight as our subject. When I meter on this, I can get a good exposure by using these three settings:

  • The initial shutter speed is 1/80th of a second
  • The aperture is f/2.0
  • The ISO is 640
1/80th sec — f/2.0 — ISO 640

What's interesting is that I can also get a good exposure with wildly different settings. In this photo I've used these settings:

  • 1/400th of a second shutter speed
  • f/1.4 aperture value
  • ISO rating of 1600
1/400th sec — f/1.4 — ISO 1600

And then in the very next image, I've used:

  • Shutter speed of 6/10ths of a second, which is pretty slow
  • Aperture of f/5.6
  • ISO rating of 100
6/10th sec — f/5.6 — ISO 100

In fact, I can get a good exposure from thousands of combinations of aperture, shutter, and ISO. This is what is known as the exposure triangle. Since all of these settings are dependent on each other and connected, when one setting changes, the other ones must also change in order to achieve the same exposure.

With all of these possibilities for achieving the correct exposure, which one should you choose? Well, this is where you get to make creative decisions with your photos. You see, not only do these settings affect exposure, but they also affect your images in other ways.

Shutter speed affects the amount of motion blur in your images. A slow shutter speed allows more motion blur of an image while a fast shutter speed freezes action and gives you a nice crisp photo. Here are a couple of examples with different shutter speeds.

In this example, we're using a shutter speed of 1/30th of a second. As you can see the car moving by has been motion blurred by the slow shutter speed. You can see the streaks of where the car was, but you don't see a lot of detail on the car.

Now here's a very similar photo, only, now we have used a faster shutter speed of 1/500th of a second, which has frozen the action of the car driving by, and we get to see a lot more detail and it's a lot more sharp.

Shutter speed not only freezes the action of our subject, we must also use a shutter speed fast enough to freeze the motion blur caused by the movement of our camera. In this photo, the shutter speed was too slow at 1/10th of a second, and caused a blur from the camera shake.

Basically when my hands move when I take a picture it shakes, and that caused some blurring in the images. The generally accepted rule on the slowest shutter speed that you should use when shooting handheld is one, divided by the focal length of your lens. So a shot with a 100mm lens, I should have a minimum shutter speed of 1/100th of a second to avoid motion blur from camera shake. Aperture also has another affect on your photos besides exposure known as the depth of field.

Depth of field is a term that describes how much of your photos is in focus. Here's an example of a photo taken with a pretty small aperture of f/11, and as you can see, much of the scene is in focus.

However, if we take the same exact photo with a much larger aperture of f/2, you'll see quite a difference in that most of the scene is now out of focus.

When we want more of our photo in focus, we can use a smaller aperture to get it. When we want to pull our subject off of the background, blurring the background and keeping our subject in focus, we can use a larger aperture to do that, too.

Finally, ISO also has an effect on your photos other than its effect on exposure. Basically, the more you turn up the ISO, the more noise you're going to introduce to your image.

High-ISO noise creates little spots and grains of different colours. It's never nice to see an image with too much noise, so use the lowest ISO that's possible to get the images that you want. That said, newer cameras and software are effective at reducing the negative sides of high-ISO noise, so if you can use RAW formats, go ahead and try boosting the ISO if you need to get the exposure. You're better off with a high-noise image than no image at all.

Enjoy!

You now have almost complete creative control of your camera by just being able to control these three settings. It's pretty exciting, and I hope you can go out and play around with them and kind of get a feel for how it works until you're really comfortable with using them.

In the next lesson we're going to be going over small flashes that are built into our cameras and how to get the most out of them.

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