EXPOSURE Image & Camera Control Instructor: David King

Exposure: Definitions TOTAL “EXPOSURE” is the TOTAL amount of light used to render an image on a light sensitive medium (such as film, paper, or digital imaging chip). Over Exposure means too much light was used Under Exposure means too little light was used. Exposure: Image & Camera Controls Instructor: David King

Exposure: Samples Exposure: Image & Camera Controls Instructor: David King UNDER Exposed Proper Exposure OVER Exposed

Exposure: Getting it right To determine a correct exposure we need to know two bits of information… 1.How sensitive is our medium? 2. How much light is on our subject? Exposure: Image & Camera Controls Instructor: David King

Exposure: Getting it Right How Sensitive to Light is the Medium? ISOLight-sensitive media are rated in “ISO*” numbers. The higher the number the more sensitive the medium (the less light it will require for an exposure) ISO Numbers (and all exposure calculations) follow the “Base 2” logarithmic system As the number doubles, so does the sensitivity… meaning… It takes ½ the amount of light to properly expose it. * ISO = International Standards Organization Exposure: Image & Camera Controls Instructor: David King

Exposure: Light Meters How Much light is there? Light is measured by a LIGHT METER There are TWO types of light meters… –INCIDENT LIGHT METERS, and –REFLECTIVE LIGHT METERS Both types of meters are designed to base their readings on middle gray. So we need to explain that before we can go on… Exposure: Image & Camera Controls Instructor: David King

Exposure: Light Meters 18% Gray Card… Photography’s “standard” for “middle gray” Exposure: Image & Camera Controls Instructor: David King This is the tone the light meter will think it is seeing, and into which it will turn whatever it is actually pointed at. (YOU NEED ONE OF THESE…)

Exposure: Light Meters INCIDENT LIGHT METERS Incident Meters read the light striking the subject (called “incident” light) Incident meters are placed near the subject and aimed back at the camera They have a “collecting” dome or panel that diffuses and averages the light to give a true “gray Card” exposure. That means that an 18% Gray Card placed in the scene will be rendered accurately on the film, print, or file. Exposure: Image & Camera Controls Instructor: David King

Exposure: Light Meters REFLECTIVE LIGHT METERS Reflective meters measure the light being reflected off of the subject back towards the camera. They are aimed at the subject from camera position. They are programmed to assume their target is approximately middle gray and give an appropriate reading for that amount of reflectivity. –Remember! That means they will give a reading that will turn whatever tone they are actually seeing into a middle grey. –If they are not being aimed at middle gray then the photographer must compensate for the difference. Exposure: Image & Camera Controls Instructor: David King

Exposure: Light Meters REFLECTIVE LIGHT METERS (cont.) In-Camera Meters are all “Reflective” meters and respond just like any other reflective meter. Most DSLR camera meters can be set in the following modes… –Averaging –Matrix Metering (a Nikon term) using selected areas –Center Weighted –Spot Exposure: Image & Camera Controls Instructor: David King

Exposure: Light Meters BOTTOM LINE Light Meter readings are a GUIDE to your exposure but need to be carefully analyzed and its indications modified to fit the target and the scene. Modern Digital Cameras provide a technically wonderful test of exposure in their HISTOGRAM function but we’ll deal with that later. Once we know the sensitivity of our film or sensor and take a light meter reading based on it, we are ready to work with that data to make an exposure Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements An EXPOSURE is comprised to two major elements: The Intensity of the Light (How bright) and The Duration of the Light (How long) These two elements both constrain and allow technical and aesthetic command of photography. Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements The Intensity and Duration of the light can be thought of as similar to water flowing into a bucket… Exposure: Image & Camera Controls Instructor: David King The Capacity of the bucket – one gallon – represents the total exposure…

Exposure: Elements The Intensity and Duration of the light can be thought of as similar to water flowing into a bucket… Exposure: Image & Camera Controls Instructor: David King Water flowing through a small pipe (think Intensity) will take longer (think Duration) to fill the bucket Time to fill: 95 seconds

Exposure: Elements The Intensity and Duration of the light can be thought of as similar to water flowing into a bucket… Exposure: Image & Camera Controls Instructor: David King But if we get a bigger pipe (think “open the aperture”) water can gush in faster (greater intensity)…

Exposure: Elements The Intensity and Duration of the light can be thought of as similar to water flowing into a bucket… Exposure: Image & Camera Controls Instructor: David King …and the bucket can be filled faster (shorter duration) Even though the total amount of water remains the same. Time to fill: 25 seconds

Exposure: Elements With these two elements of the EXPOSURE, if you increase one of them, you must decrease the other to maintain the same total amount of light. And we have a rule to tell us how much we have to change the second element to compensate for the changing the first. Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements The two major elements exist in a reciprocal relationship called to: THE LAW OF RECIPROCITY Exposure: Image & Camera Controls Instructor: David King Simply stated: The “Law of Reciprocity” holds that to maintain a given total exposure, if you change one element, you must compensate with the other in the opposite direction but by the same amount. So how do we change these elements?

Exposure: Elements: Controls The two major elements each have a camera control that is used to adjust them to allow for more or less intensity or more or less duration of the light. Exposure: Image & Camera Controls Instructor: David King Any camera that allows manual control will have these… they just might be in different locations on different camera or lens bodies.

Exposure: Elements: Controls Each camera control has it’s own incremental settings to allow very precise control over the exposure. Exposure: Image & Camera Controls Instructor: David King These settings correspond to the Base-2 system we mentioned earlier. You’ll see…

Exposure: Elements: Controls f STOPS : F-Stops control the intensity of the light going through the lens by opening and closing an aperture. These were derived from “Waterhouse” Stops. The F-number is a ratio between the focal length of the lens and the diameter of the aperture Each whole number changes the light by a “Stop” – a factor of 2. Because it is a mathematical ratio, as the number gets larger the aperture gets smaller… Sorry… Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements: Controls SHUTTER SPEEDS : Modern electronic shutters allow almost any speed but initially these were set increments with no “on-between.” Shutter speeds are normally fractions of a second unless noted otherwise. 1S.. ½.. ¼.. 1/8.. 1/15.. 1/30.. 1/60.. 1/ / / /1000 The jump in increments is due to attempts to combine several old standards for shutter speeds. Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements: Controls Each camera control has an effect on the way the image will look and becomes a powerful aesthetic too. Exposure: Image & Camera Controls Instructor: David King Just remember, if you change one you must compensate with the other!!!

Exposure: Elements: Controls DEPTH OF FIELD: Depth of Field is the area in front of and behind the subject (or point of critical focus/the focal distance) that appears to be in focus in the photograph. It is an illusion resulting from: –The camera lens projecting light rays as tiny circles (called Circles of Confusion ) that increase in size as they are from distances farther and farther away from the point of critical focus. And… –The human eye’s inability to resolve detail smaller than 1/200 of an inch. –Therefore, if a Circle of Confusion on a print is smaller than 1/200 of an inch that area of the print will appear to be in focus. Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements: Controls DEPTH OF FIELD, (Cont.) Here is an example of Depth of Field in action. Exposure: Image & Camera Controls Instructor: David King f4 f22

Exposure: Elements: Controls DEPTH OF FIELD (Cont.) Here is what we are talking about... Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements: Controls DEPTH OF FIELD (Cont.) Why it happens… Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements: Controls MOTION: Motion is indicated by a blur of the image when there is movement relative to the subject and the film plane. Motion can be a case of… –Camera still and subject moving –Subject Still and Camera Moving –Both Subject and Camera moving The slower the shutter speed (longer duration of exposure) the greater the blur will be. For example… Exposure: Image & Camera Controls Instructor: David King

Exposure: Elements: Controls MOTION: Motion is indicated by a blur of the image when there is movement relative to the subject and the film plane. Exposure: Image & Camera Controls Instructor: David King Example: Camera Steady And subject moving

Exposure: Elements: Controls MOTION: Motion is indicated by a blur of the image when there is movement relative to the subject and the film plane. Exposure: Image & Camera Controls Instructor: David King Example: Camera panning with moving subject and medium shutter speed..

Exposure: Elements: Controls MOTION: Motion is indicated by a blur of the image when there is movement relative to the subject and the film plane. Exposure: Image & Camera Controls Instructor: David King Example: Fast shutter speed to freeze motion

Exposure: Elements: Controls MOTION: Motion is indicated by a blur of the image when there is movement relative to the subject and the film plane. Exposure: Image & Camera Controls Instructor: David King Example: Camera and subject in motion with slow shutter speed to create an abstract image.

Exposure: Elements: Controls EQUIVALENT EXPOSURES: All of the exposure combinations below result in the same TOTAL EXPOSURE ! Exposure: Image & Camera Controls Instructor: David King Understanding the use of Equivalent Exposures is a key to really controlling your images.

QUESTIONS…???

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