Jim Mathis
10851 Mastin Suite 130
Overland Park, KS 66210
913 269-6709
Jim@MathisPhoto.net

 

Camera Controls

Camera Controls

To move beyond the “point and shoot” approach, the photographer needs a good understanding of camera controls, how they work, and how they affect exposure and why that is important.

 

Exposure Controls

Film is designed with a specific sensitivity. In other words, to get the best results a very specific amount of light is required. This is called the speed of the film. The term “speed” is used because in the early days it had to do with how long it took to get the correct exposure. More sensitive films are said to be faster. Films might be given an ISO rating of 50, 100, 200, 400, 800, etc. (ISO stands for International Organization for Standardization. It is headquartered in Geneva, Switzerland.) Each time the number is doubled, half as much light is needed. Doubling or halving the light is called “one-stop.”

The terminology has carried over to the current digital era. CCD and CMOS chips used in digital cameras have a native or natural sensitivity. This is often around 100 ISO. The signal coming from the chip can be amplified to increase the sensitivity resulting in a rating comparable to film using the same numbers: 100, 200, 400, 800, and so forth. When the signal is amplified it picks up noise which looks a little like the grain associated with higher-speed films. The amount of noise at higher ISO speeds is a factor of the quality of the sensor, its size and the quality of the electronics. There is a strong relationship between these things and the cost. More expensive cameras have less noise at higher speeds.

There are only two ways to control how much light enters the camera. Thinking in terms of letting fresh air into your house, you can open the windows more, or you can leave them open longer. If a person wanted to fill a bucket with water, he could control how long the faucet is on, and how much water comes out at a time. It is the same with exposure. How big the window is is called the aperture or f-stop. The length of time the window is open is called the shutter speed.

 

Shutter Speed

Shutter speeds are given in fractions of second. Common shutter speeds are 1/30, 1/60, 1/125, 1/250, 1/500 of a second. If the photographer were to expose the image for five minutes or for 1/8000 of a second, it is still called the shutter speed. Each step halves or doubles the amount of light the shutter lets in.

In addition to determining how much light enters the camera, the shutter speed also has an effect on the subject. If the subject is moving, a slow shutter speed will render the subject blurry. A fast shutter speed will stop action. One of the biggest contributors to unsharp pictures is camera movement. The problem of camera movement increases dramatically with slower shutter speeds.

The implications of this are tremendous. Using the shutter speed control the photographer can stop a race car on the track or intentionally blur a runner’s leg to give an illusion of motion. In photographing sports, the photographer can decide if he wants to freeze the ball as it enters the goal or does he want to show the blur of players surrounding the ball.

To stop camera movement at slow shutter speeds a sturdy tripod is required. At higher shutter speeds a tripod is not necessary unless the photographer wants to walk away from the camera and fire it remotely for some reason.

The definition of which shutter speeds are slow and which are fast is a long-running discussion among photographers. This is complicated by factors such as the size and weight of the camera, the skill of the photographer to hold the camera steady, and the focal length of the lens.

A rule of thumb is that a photographer can safely hand-hold a camera with a shutter speed equal to or faster than one over the focal length of the lens. In other words, if the photographer is using a lens set at the 50mm setting, he could assume that his pictures would be sharp at shutter speeds of 1/50 or higher. This becomes an issue when using very long telephoto lens, especially in very low light. The opposite is also true. Wide-angle lens allow the use of slower shutter speeds without a tripod. This rule varies from camera to camera and photographer to photographer. It is a good idea to test yourself and your camera to see at what shutter speed camera movement becomes a problem in your pictures. Some cameras flash the shutter speed indicator or change color of the read-out if the shutter speed is too slow to hand-hold, but this is only a guide, your mileage may vary.

To test your slow-shutter speed skills, try photographing a spot of light such as a laser pointer on a wall. Using various shutter speeds, one can easily see at what speed the dot becomes a streak.

Many modern cameras have an electronic image stability system. This system generally allows the photographer to use shutter speeds one or two speeds slower than would be possible without it. This feature varies from one camera model to another. Again, it is a good idea to experiment with your camera to see how much difference it makes.

Another useful technique is panning. Panning is following the subject movement with the camera and then tripping the shutter at an appropriate time. This technique is used to photograph race cars, runners, or any subject moving at a predictable rate and direction. In panning it is a good idea to turn off the stability control and use manual focus as well.

The manufactures specification will give the minimum and maximum shutter speed the camera is capable of using.

An example of using a slow shutter speed and panning to give the feeling of motion.

An example of panning and a high shutter speed to stop action. Note one-third rule. Also note that the planes are moving into the frame, not out of it. This is a good rule of composition.

 

F-Stops

The other control for exposure is the aperture. This is the size of the opening in the lens. A larger opening lets in more light and a smaller opening lets in less light. The size of the opening is stated as a ratio of the size of the opening compared to the focal length of the lens. A 50mm lens with a 50mm opening would be called f/1. If the lens opening of a 50mm lens were 12.5mm we would call it the opening f/4. As the focal length of the lens changes, the opening must change to keep the same F-number. A lens with a larger opening is said to be “faster.” A f/2.8 lens is one stop faster than a f/4 lens.

Lenses are rated according to their maximum possible f-stop. This usually is determined by the physical size of the lens. A PS camera might have a zoom lens with a range of 6-20mm and a maximum f-stop of f/2.8 to f/4.9. That means at the wide-angle setting of 6mm the lens opening is 2.14mm and at the telephoto end of 20mm it is an opening of 4mm. A larger DSLR camera will often have faster lenses because there are fewer size restrictions.

The standard f-stops are: f/1, f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f32, and so on. Each step up or down doubles or halves the amount of light that the lens lets in. For example f/4 lets in twice the amount of light as f/5.6. There are in between settings such as f/3.5 or f/4.8. These may or may not be half-stops depending upon how the lens manufacture chose to label the settings.

Each step up or down is called a stop. Since changing the shutter speed in even increments of doubling or halving the speed is also called a stop, we can use the term interchangeably whether we are changing the shutter speed or the aperture. “One stop” changes the exposure the same whether we are changing the shutter speed one stop or the f-stops one stop.

Photographers use the term “stopping down” to indicate that less light is let in or “opening up” to indicate more light is let in. On a bright sunny day the camera would stop down. On a cloudy day it would open up. Modern automatic cameras do this automatically, but it is a good idea to know the correct terms.

 

Depth of Field

In addition to controlling the amount of light entering the camera at a time, the aperture also affects the depth of field. Depth of field is nothing more than how much of the subject is in focus. Depth of focus has to do with the area behind the lens that is in focus. This is mainly a concern to camera and lens designers.

The higher the f-stop, the greater the depth of field. At a high f-stop of f/11 or f/16 for instance, a large area front to back will be in focus. A photographer would want to use a high f-stop for scenic photos where it is important for everything from the near foreground to the distant mountains to be sharp. If the photographer wanted to isolate the subject from the background by causing the background to be out of focus, he would want to use a lower f-stop number, which is a larger opening. Remember: f-stop is a ratio, the larger the opening, the smaller the number.

Depth of field is also affected by the focal length of the lens. The longer the focal length, the shallower the depth of field. The shorter the focal length, the more depth of field. Wide angle lens have more depth of field than telephoto lenses. This is why we typically use wide-angle lenses for landscapes where we want everything sharp, lots of depth of field; and telephotos lens for portraits where we want the background to be soft and out of focus, shorter depth of field.

Depth of field is also affected by the distance from the camera to the subject. The greater the distance, the greater the depth of field. As the camera gets closer to the subject, the depth of field decreases.

Here is an example of shallow depth of field, selective focus, and compression due to telephoto effect.

To get everything in focus use a high f-stop and a wide-angle setting. To get the least amount in focus, use a low f-stop and a telephoto setting.

In practice, with wide-angle lenses, at moderate to high f-stops, and at normal to longer camera to subject distances, the depth of field is so great that there is hardly a need to focus. For this reason, some inexpensive cameras with slow wide-angle lenses have no focusing system. These are called fixed-focus camera. Focus becomes critical with telephoto lenses, fast f-stops, and/or close focusing distances.

 

Putting it all together

Through all this, the exposure has to be correct. That means that the f-stops and shutter speeds work together. If the f-stop is raised, the shutter speed must be lowered and vice versa. If say, the correct exposure for a given amount of light were 1/60 at f/8; the photographer could also use 1/125 at f5.6, 1/250 at f/4, 1/500 at f2.8, 1/30 at f/11, 1/15 at f/16, or 1/8 at f/22. These are all the same amount of light as far as the sensor is concerned. Using this concept the photographer can control how action is recorded, affect of camera movement, and depth of field just by switching between various shutter speeds and f-stop combinations.

Digital cameras usually have a fully-automatic setting indicated by a green square. In this position all manual controls are shut-off and the camera makes all the choices.

There is also usually a “P” position for program. In this position the camera chooses the appropriate combination of shutter speeds and f-stops to give the best picture in most situations. In the “P” position the camera manufacturer decided when it would be best to open up the f-stop and when it would be better go to a slower shutter speed and so forth following a pre-determined program. Most often, this works fine, but the program cannot anticipate every possible photographic situation. Most cameras have some sort of “scene” control where the program setting can be adjusted for different situations. For example if you set the camera to ‘Mountains” higher f-stops are favored, and so forth. A portrait setting would favor lower f-stops.

As you move up in price, cameras begin to have shutter priority, “S or T,” and aperture priority, “A” settings. In these positions you can set either the shutter speed you prefer or the aperture you prefer and the camera sets the appropriate corresponding aperture or shutter speed. Once the photographer has a clear understanding of how these two controls affect the photo, these become very useful controls and the “scene” settings become less useful.

In the manual or “M” position both shutter speed and aperture can be set manually. With many cameras a meter will become visible in the manual setting to show whether you are over or under exposed.

Many cameras also have a “B” or bulb position. The name “bulb” comes from the old days when camera shutters were tripped with a rubber bulb using air. The shutter speed could be controlled by how hard or fast the bulb was squeezed. If the photographer squeezed the bulb slowly and held it, the shutter would stay open until the bulb was released. Today, in the “B” setting the shutter remains open as long as the button is held down. This is used for very long exposures and other special effects.

P, S, A, and M are all useful settings and the photographer should take the time to read the manual and understand how each works. The large number of models and manufactures, along with continual updating and improvements mean that it is hard to make uniform statements about where these controls are located and how they react, but the principles are the same. A good understanding will allow the photographer to pick-up any camera and quickly figure out its handling characteristics.

 

Sensor Sensitivity

The next thing to consider about exposure is the sensitivity of the chip that captures the image. Most cameras use either CCD or CMOS chips and there will surely be others in the future. Too much light will cause the chip to overload resulting in everything being white. Too little light will cause everything to be black. In between, if the exposure isn’t right, the light colors in the subject will block up – no detail in the white or lighter colors, or the shadows will lose detail due to not enough exposure in the darker areas. The same results happen with film that is over or under exposed.

We use the shutter speeds and f-stops to control the amount of light, but the chip also has some adjustment capability. Particularly the camera can amplify the signal to produce a better picture with less light. The sensitivity of the chip is given as an ISO number which compares to the ISO number of film.

Generally speaking a lower IOS setting will render better color with less noise or other distortions, but don’t be afraid of higher ISO settings if the situation calls for them. Many cameras will produce excellent results at ISO 1600, 3200, or higher.

Some cameras now allow the photographer to set the shutter speed and aperture manually and let the camera choose the appropriate ISO setting for the sensor.

Again, read the owner’s manual to determine how a particular model of camera sets the sensitivity based on various settings and situations.

 

Histograms

Many cameras will allow the photographer to view a histogram on the LCD window. This graph shows the distribution of light and dark areas over the sensitivity range of the sensor. This allows the photographer to make sure that important areas of shadows and highlights are not being lost.

 

Other Controls

 White Balance

The color of light varies greatly. On a sunny day the light will be blue. An incandescent light bulb is quite yellow. The human eye adjusts to these various lighting conditions but film cannot. Film is rated as to its color temperature or color balance. Digital cameras can adjust to the various colors of light in much the same way as the human eye. It does this by assuming that all of the colors in the image when mixed together will come out white or shades of gray. This is called the “white balance.”

Most of the time this works fine, but not always. If there is a predominance of one color in the subject, say a close-up of a red dress. The camera will assume that the light is reddish and try to correct for all that red. The result may still be a red dress, but the colors will be much less vivid than they could be. The solution is to use the manual white balance control. Inexpensive cameras may not have manual white balance or it may be hidden in a menu making it unhandy to use. DSLRs or more sophisticated cameras will probably have a “WB” button that brings up a choice of several settings.

Color is rated in terms of degrees Kelvin. Daylight is roughly 5000° K. Tungsten lights are about 3200° K. Most advanced cameras will allow the photographer to set the “K” number or will have some symbols such as a sun or a light bulb. Most cameras also allow the camera to read the color off of a white object. To do this, point the camera at a white piece of paper or other white object held in the same light as the subject. Push the white balance lock, the camera sets the color off the white object and you are all set. This is the standard procedure in video or movie production.

Most DSLRs have a variety of white balance settings allowing the photographer to set white balance in several different ways. In difficult lighting situations such as photographing a stage presentation with changing colored lights, it may be necessary to experiment to see which setting works best. This is one of the huge advantages that digital has over film. Photographers don’t have to wait days to see if they guessed right in difficult light situations. For most situations AWB or automatic white balance works fine. Just be aware that in some situations it must be set manually.

With film, color temperature was usually corrected with filters or later in the darkroom to some degree. Digital allows for more accurate color balance in the camera with further corrections in the computer.

Some light is not continuous and therefore it is not possible to give it a Kelvin temperature number. Fluorescent lights, mercury vapor lights, neon, and a few others are in this category. Modern digital cameras do a remarkable job of correcting these kinds of lights, but be aware that it may not be possible to get the colors perfect in every lighting situation.

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