Exposure Expose`

Correct exposure is the sum total of the ISO setting, your shutter speed setting and the aperture setting on your camera.I continually see Twitter tweets with folks passing on 140 character advice about how to use aperture or shutter settings on a DSLR. Hence, I continually cringe thinking through the scenarios that must result from those suggestions.

For instance; "Always shoot aperture priority and your pictures will be sharp." Well, not if it's in a dark room and your aperture priority selection forces the shutter speed down to 1/4 sec. And I loved this little piece of expert advice; "I know, it's tough to deal with. Lowest aperture, high ISO, & shoot with about -1 stop on exposure, or use manual. 1/40-60th maybe?" Wow… take that and go print up your business cards… you're ready.

Let's set the record straight. For one thing, if photography were simply a matter of saying "do this" then "do that" everyone  would be good. Better yet, automatic cameras would get it right every time. You wouldn't even need to bother with "settings." I want to walk you through the basics of each of your camera adjustments and discuss how they effect the exposure. Then I will go a little deeper and discuss how those adjustments can effect your picture and the creative decisions you make.

First you need to understand that a correct exposure is the sum total of the ISO setting, your shutter speed setting and the aperture setting on your camera. Each of these settings provide control over how we manage the light hitting our film or digital sensor. Remember, this is "the science of light." Since I noticed your eyes just got glassy I'll describe each one of those things.

With digital cameras, the degree of noise and detail loss due to high ISO will vary based on the camera you are using. The newer cameras are getting exceptionally good. Shot at 6400 ISO.ISO: ISO is the rating used to define the sensitivity of the sensor or film to light. A low ISO setting… say 100, is going to require more light to create an image. A high ISO setting.. say 800, is going to require less light. So choosing the ISO setting is based on the kind of lighting situation we're faced with. If it's a bright sunny day, we can set the ISO low. If it's a medium cloudy day, we may want to set it a bit higher. If we're in a low light setting, we'll want an even higher ISO setting.

The trade off to this is use a higher ISO setting we inherit what is called noise or grain. This results in a loss of detail, especially in the shadows and lower light areas of our shot. With film, the challenge was for film producers to produce high ISO films with reduced or finer grain. With digital cameras, the degree of noise and detail loss due to high ISO will vary based on the camera you are using. Newer and advanced cameras are putting lots of research and development into high ISO capabilities of their cameras. The newer cameras are getting exceptionally good.

As we leave the ISO description, think of ISO like octaves in music. Though the octave may be higher or lower, the eight notes still combine to make the same scale. Shutter speed and aperture (f/ stops) will be combined to make the eight notes on our musical scale regardless of the ISO (octave).

Using the same aperture setting, the photo on the right was shot at 1/500 sec. while the one on the left was shot at 1/250 sec. The slower shutter speed resulted in an overexposed image.Aperture: In your lens there is an aperture. This is the adjustable opening that lets the light fall onto the film or sensor. The aperture is adjustable to make a tiny opening or a really large opening - and everything in between. This opening is defined by f/ stops. Now the numbers of f/ stops can cause some confusion. That is because an aperture setting of f/11 has a smaller opening than a setting of f/2. This is something  you must hammer home to yourself. F/11 will allow less light into your camera than f/2. Seriously, you have to get this part sorted out or you'll never grasp the rest. f/11 allows less light into the camera than f/2. Commit that to memory.

Shutter: The shutter opens and closes the aperture opening and sits between the aperture and film/sensor to control the amount of light allowed to pass through the aperture and fall onto the film or sensor. The speed in which it opens and closes is determined by the shutter setting. This is done in varying increments. It can be anywhere from 1/8000 of a second on some cameras to minutes if your camera has a bulb setting. For the most part, though, you'll find many cameras are adjustable from 1/2000 of a second to 4 seconds. It's going to vary with each camera.

Now we've identified the three components required to reach our correct exposure we need to understand how each is applied.

Let's make an assumption that we are strictly discussing a CORRECT exposure.

These images where shot at the same time and location. However, the black interior required a different exposure setting than the tan interior.Instead of talking about a photo though, lets describe our correct exposure as a FULL glass of water. In order to have a correct exposure the glass must be full. If the glass is not full, we're underexposed. If water is spilling out of the glass, we're overexposed.

The glass is our sensor or film. The water will be our substitute for light. Our faucet will substitute for the camera/lens combination. The size of the stream of water is our aperture. The speed of the flow of water is our shutter.

Put the glass under the faucet. Turn on the faucet until you have a thin stream of water flowing slowly. It will take sometime to fill the glass. Now turn on the faucet until it is gushing out a blast of water splashing all over the place. The glass gets filled rather quickly.

Now comeback to the aperture and shutter. If we're going to allow the light to blast in, we need a quick shutter speed. If we're going to allow the light to stream in slowly, we need a slow shutter speed.

Let's call our correct exposure (of full glass of water) X. Our aperture (stream of light) is A. Our shutter (speed or flow of light) is S. We now know that it will take a controlled combination of A + S = X

Control means having the knowledge to make decisions that directly affect the image you want to make, not just the image the camera wants to take.And the ISO? I guess you might think of that as the source of our water. Using the kitchen sink (low light source), the garden hose (better light source), a fire hydrant (good light source) or Niagara Falls (an unmanageable light source)? The sink would require a high numbered ISO and Niagara Falls would require a low number ISO.

I know at this point  you want to flip that knob over to the magic Green Square setting on your camera… or get really creative and choose one of those pretty little scenery icons. Don't despair. You'll get it. And you'll get it in a way your camera can't. You can think and anticipate. Your camera can only assume.

Metering

There are two ways to measure light. 'Reflective' metering and 'incident' metering.

A handheld light meter gives us the choice of measuring light both ways, 'reflective' or 'incident.' Reflective measures light bouncing OFF your subject whereas an incident reading measures the light falling ON to your subject. Do you recall ever having seen a photographer walk up to a model and hold a meter under the model's chin? He's taking a an incident reading. He's measuring the actual light falling onto the subject. Obviously, this is much more accurate.

The metering system in your camera is "reflective". That is to say, it measures light as it is reflected back onto the film plane or sensor.  And therein lies the rub with reflective metering. If you're in the bright sun looking at something bright white, it hurts your eyes… right? Whereas if you look at something black, it's not a problem. Even though the white is bright for you to look at, you're pupils (the human equivalent of an aperture) adjust automatically. The camera's meter as no way of accurately adjusting for that. Sure, some camera models will try to average the scene, but if you're taking a photo of 6 guys in white shirts and two guys in black shirts, the camera's meter is going to read a lot more light than the camera/film/sensor actually needs.

Our challenge is to outsmart our camera's reflective metering.So our challenge is to outsmart our camera's reflective metering.

How do we do that? Simple. We make the decision to either let in or keep out some of the light by adjusting the aperture or shutter speed based on the scene we are photographing. Meters are calibrated to accept a value of 18% of black (a light/medium gray) as average. We have to try and average out the reflective values of the overall scene and cheat the camera's metering. So speed up or slow down the shutter speed. Or, open up or close down the aperture. Remember, we want to control the stream and flow of light so as we reach the correct exposure. If you like, you can buy a small 18% gray card and hold it between your lens and your subject and take an accurate reflective meter reading. Once you have the reading, you can manually set your camera to the aperture/shutter of your choosing. But, it is something that will ultimately come to you with experience.

Creative Application

In a perfect world, your camera would be most happy if there was a lovely ray of sunshine coming over your left shoulder casting a golden glow of light onto your subject. So, for the next part of our discussion, let's step through Alice's mirror and into the perfect world. Let's assume the sun is coming over our shoulder just right and the camera's automatic settings are doing their job getting a correct exposure. Now we've got GREAT photos, right? Wrong. We've probably got nice photos, but we want GREAT photos. Camera's can not think creatively. That's where you come in.

Shallow depth of field enhances the look of this vintage hood ornament. At f/4, the 1/2000th sec. shutter speed was inconsequential. The "bokeh" of the highlights behind the image add impact.The only way you're going to get GREAT photos is understanding what we've discussed above. That's why photography courses and pros will talk to you about photographing eggs and still-life studies and even shooting black and white exclusively. Learning the basics puts you in control of the light. You need that control if you're going to get creative. It's no different than any other endeavor you can think off. If you want to get good, you must be in control. While subject matter and composition make up the story, understanding and seeing what the light is doing is critical to making great images.

Each of the camera settings we're discussing become creative tools once they are under your control. If they're not under your control, they're going to do whatever they want leaving you frustrated and asking "why don't my pictures look like that (whatever picture you're pointing at)?"

Locate the shells that are in focus. Now look in front of and behind them. Notice the graduated shift of sharp to unsharp? The area remaining sharp equates to your depth-of-field.Depth-Of-Field: One of the first creative measures you can apply is controlling the depth-of-field. Depth-of-field is the area of the image that is in focus. Imagine an archery target lying flat on a table and a bottle standing up on the bullseye. With the bottle correctly focused, if we look at the rings around the target, we'll notice the degree of sharpness increases the closer they are to the bottle and decreases in sharpness the further away they are from the bottle. Notice also, it's basically the same in the foreground and in the background. The area that remains in focus with the bottle is referred to as our "depth-of-field." We can control the depth-of-field by adjusting our aperture setting.

The smaller opening… let's stick with F/11 is using more of the center of your lens. The physical properties of a lens dictate that the center of the lens is the optimum point of sharpness. I think of it like a flame, it is the hottest and its very tip. Sharpness may vary with the quality of lens, but it will still display the same characteristics across the face of the glass. The center is the sharpest. As we move toward the corners lens sharpness becomes challenged.

Using a small aperture opening (large number f/ stop) will give us more depth-of-field.. a greater area of sharpness. Using a large opening (small number f/ stop) will give us a shallow depth-of-field… or less area in focus.

Portraits are always improved when you can control the depth-of-field. The soft blurred background makes your subject stand out.Why would you want a shallow depth-of-field… don't we want everything sharp? Creatively speaking, not always. If I'm doing a landscape, sure, I want all the sharpness and detail I can get. Or, if I'm shooting a beauty shot of a classic car, I want all the car in focus front to back. But, let's say my car shot background isn't the greatest of is a bit cluttered, then I'm going to want to find a depth-of-field that will keep all of the car in focus but have the background blur out.

A common use of shallow depth-of-field is with portrait work. It portraiture, the challenge is often to find exactly the right depth-of-field that keeps the nose, eyes and almost the ears tack sharp… and then just falls off a into buttery smooth softness giving our photo and subject an almost 3D effect.

While I don't want to over complicate the discussion, it is important that you understand depth-of-field can also vary depending on the focal length of the lens used and the distance between your subject and the background. The principles do not change, however the degree of the creative effect will have variables.

Give some thought using and applying depth-of-field selectively and creatively.

In this image, I was so intent on keeping my shutter speed fast (1/2500) so the butterflies quick movments wouldn't blur the shot, that I actually ended up shooting with the aperture wide open at f/2.8. At 200mm, that's an extremely shallow depth-of-field. Consequently, the back wing is slightly out of focus. Not the way I would have preferred it. An aperture setting of f/4 would have been a better bet.Shake, Rattle and Roll: Shutter speed becomes critical since it can directly affect what apertures are available to use. Remember, we need that A + S combination to get to X. You don't get to pick one without the other. Often that means compromise.

If you're not on a tripod, shutter speed can directly effect the sharpness of your photos. Why? Tremble, hand shake, even a moving subject. The shutter has to be quick enough to freeze the moment.

When we consider a lot of our shots are taken using our camera handheld, we have to address the importance of eliminating shake or tremble. A telephoto lens will magnify your tremble or shake more so than a wide angle lens. A handy rule of thumb is to choose a shutter speed relative to the focal length of the lens.

For instance; say you're shooting a subject in available light and the sun is setting quickly. Your ISO is at 800 and any higher just gets too grainy or noisy and you're aperture is wide open, if you're shooting with a 100mm lens, you're going to be hard pressed to hold the camera steady below 1/100 sec. If you're using a 50mm, you're probably going to have a tough time at much less than 1/60th sec. Even this rule of thumb requires a steady hand though, so try to find a way of bracing yourself and the camera when the shutter speeds get low.

Often there are times we want to use the shutter speed to freeze action. Sports shooters will often want to capture the ball coming off the end of a bat or racket, or perhaps stop an athlete in mid air. It's fascinating to capture moments that the human eye cant see. While you'll need to experiment with what shutter speed will actually freeze your particular subject, you'll also need to keep in mind that a faster shutter speed requires a larger aperture opening. Always a compromise.

Freezing an image won't always tell the story in an action photo. This was shot by "panning" the car and using a shutter speed of 1/125 sec.Freezing the action isn't always the best way to tell the story, though. In some sports, particularly motorsports, you don't want to freeze the action. On the contrary, you want to capture and show the action. If a car's wheels aren't spinning it's going to look like it's parked. How will you show your viewers that the car was literally flying past you? This is an instance where we'll use a technique called panning. Panning is where you lock a moving subject in your viewfinder and follow it while shooting with a slow shutter speed. If you've mastered the technique, the result will be a sharp race car with a streaked background and spinning wheels. A good motorsports shooter can easily pan with a 200mm lens at 1/125 sec. and lower… often much lower.

Panning the car at 1/15 sec. and tossing in a touch of flash to light up the irridescent graphics.For obvious reasons, it's hard to teach creativity. These are just a few examples of how you can apply the camera's settings creatively.  But, you've got to have control of your tools. With control, as you learn and develop your own vision, you'll know what tools to apply and how to manage them to capture the image you "see."

I know this is a lot to digest. However, it is one of those things that once you understand, it will all begin to fall into place and truly accelerate you to the next level in your photography.

Selective focus: In this shot, the depth-of-field is used selectively to bring the viewers eye to the car in the background rather than the car in foreground.If I could make one suggestion it would be to get a handheld meter. Even the most basic model will help you. The beauty of a handheld meter is after it takes the reading it will then provide you with all the available combinations that will result in an accurate exposure. This allows you to concentrate on choosing which combination will provide the right creative choice. And it's also a learning tool. You'll find the more you use a handheld meter, the less you need it.

If you want basic photos, slap that camera in automatic and forget we ever met. If you want great photos, learn the basics. You can't have one without the other.

JT