Lunch & Learn, Photo Basics

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Information about Lunch & Learn, Photo Basics

Published on February 9, 2014

Author: exhar



I presented Photo Basics to a room full of pizza eating designers, researchers, and engineers as part of a series of lunch time presentations at Insight Product Development. The focus was on covering the basics that would lay the groundwork for a specialized lighting workshop targeted at improved photography for each discipline's needs.

Photo Basics




Light through the lens is redirected by the reflex mirror. PENTAPRISM A pentaprism flips the image and redirects it into the viewfinder. VIEWFINDER FILM / SENSOR REFLEX MIRROR

When the shutter release is pressed, the reflex mirror flips up, sealing the chamber (from light from the viewfinder) and allowing the light from the lens to expose the sensor. PENTAPRISM VIEWFINDER FILM / SENSOR REFLEX MIRROR

Understanding exposure


Exposure DEFINED: Exposure is the total amount of light that film or an image sensor is allowed to be exposed to. Depending on the amount of light you’re photographing and the camera’s dynamic range (useful exposure range) there’s an optimum or correct exposure. Anything else, unless intentional, is either over or under exposed.

Exposure UNDEREXPOSURE Shadows are “blocked up”, losing their details and rendered as all black or at tones undistinguishable from black. “CORRECT” EXPOSURE OVEREXPOSURE Highlights are “blown out” or “washed out”, losing their details and rendered as all white.

Exposure CONTROLLING EXPOSURE There’s a number of interdependent variables that can be manipulated to get to the right amount of light for a correct exposure. ISO SHUTTER SPEED APERTURE LIGHTING

ISO Think: size of the bucket. LOW ISO NUMBER HIGH ISO NUMBER

ISO DEFINED: ISO is the standard system for measuring film speed, a film’s sensitivity to light. Lower ISO numbers represent lower sensitivity (a larger bucket), thus requiring more light; higher ISO represent higher sensitivity (a smaller bucket), thus requiring less light. The ratio of two ISO numbers represent their relative sensitivity (e.g. ISO 200 will take half as long to achieve the same exposure as an ISO 100, all else being equal). Digital cameras have an ISO-equivalent adjustment option, which determines the sensitivity of the image sensor.

ISO Consequences? Grain in film, noise in digital. Film emulsions are made up of silver halide grains. Faster films have larger grains that are more sensible to light, but easier to notice in prints. Faster ISO speeds in digital are instead achieved by amplifying the image signal, which unfortunately amplifies noise as well. Ironically, slower ISO speeds require longer exposures, which are likely to introduce the noise to begin with.

ISO LOW ISO HIGH ISO Noise is less perceptible, but needs more light exposure. Noise is amplified, and most evident in dark areas, but needs less light exposure. Use low ISOs (100, 200) for sunny shots (outdoors or a well lit room), or when using lighting equipment. Use high ISOs (400) for low light conditions (e.g. cloudy days) or night-time shots (800+).

Shutter speed Think: time the valve is left open. FAST SHUTTER SPEED SLOW SHUTTER SPEED

Shutter speed DEFINED: Shutter speed is the time the shutter is left open for light to hit the film or image sensor. This is often referred to as “exposure time”, where a faster shutter speed (less time open) creates a shorter exposure time. Shutter speed is measured in seconds: 30+ seconds to about 1/4000 second, and are directly proportional to light (e.g. 2 seconds will allow twice the light to hit the sensor as 1 second would, all else being equal)

Shutter speed Consequences? Motion blur. Slow shutter speeds can create motion blur from moving subjects, while faster shutter speeds can “freeze” moving subjects. Also, there’s camera movements (shakiness), making it hard to hand-hold a long exposure.

Shutter speed FAST SHUTTER SPEED SLOW SHUTTER SPEED Movement is “frozen”, but produces less light for exposure. Movement is blurred, but produces more light for exposure. Use faster shutter speeds (1/250 - 1/1000 second) to freeze slow movement like walking; faster (1/500 - 1/2000 second) for fast movement like running. Use slower shutter speeds (1 - 4+ seconds) to capture motion, but use a tripod or similar support.

Shutter speed HOW DO SHUTTERS WORK??? Conventional camera shutters have a slit in them (technically, the gap between the two “shutter curtains”), which travels from one side of the sensor to the other, allowing light to hit it. Shutter speed is determined with the width of this slit and the time it takes it to travel the length of the film/sensor. LIGHT SHUTTER FILM/SENSOR

Aperture Think: the diameter of the spout. SMALL APERTURE LARGE APERTURE

Aperture DEFINED: An aperture is an opening that controls the “area” over which light can pass through the lens. Aperture settings are measured in f-numbers or f-stops, which correspond to the focal length to effective aperture diameter. An f-number of f/1 would mean the aperture is completely open, while f/2 would be half that diameter (think 1/2 = 0.5). The larger the aperture (smaller number, if not thinking in fractions), the more light allowed to pass through the lens. The working aperture range is generally determined by the lens: commonly somewhere between f/1.4 and f/22.

Aperture Further, every time an f-number is halved (e.g. f/2 / 2 = f/4), the resulting f-number has a fourth of the aperture area, hence a fourth of its relative light. LARGE APERTURE SMALL APERTURE AREA F-NUMBER f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22 RELATIVE LIGHT 256x 128x 64x 32x 16x 8x 4x 2x 1x

Aperture Consequences? Depth of field. Depth of field (DOF) refers to the distance between the nearest and farthest objects in a scene that appear acceptably sharp or focused in an image. Small apertures produce larger DOFs, while large apertures produce smaller DOFs. DOFs are also affected by focusing distance. The closer the subject you’re focusing on, the narrower the DOF becomes. Focusing to greater distances (hyperfocal distance) makes the differences between small and large aperture DOFs negligible.

Aperture SMALL APERTURE LARGE APERTURE Larger DOF with more of the scene in focus, but Smaller DOF with less of the scene in focus produces less light for exposure. (appears blurry), but produces more light for exposure. Use smaller apertures (f/22 - f/8) to capture sharper images. This is especially useful for image compositing (easier to match blur profiles). Use larger apertures (f/5.6 - f/1.4) to create emphasis and isolate subjects from the background.

Aperture HOW DOES DEPTH OF FIELD WORK??? A lens can precisely focus at one distance at a time. On each side of that point, sharpness decreases gradually and imperceptibly. The DOF limits are defined when the “circle of confusion” (a perceptibly blurred point) becomes apparent. POINT IN FOCUS DOF POINT IN FOCUS LENS APERTURE FILM/SENSOR

Aperture HOW DOES DEPTH OF FIELD WORK??? Because light rays projected through a smaller aperture are relatively more parallel to each other, the DOF is greater because points are rendered acceptably sharp in the film or sensor. POINT IN FOCUS DOF POINT IN FOCUS LENS APERTURE FILM/SENSOR

Lighting Think: an aerator or other flow modifier

Lighting Lighting is in essence all the other non-camera, non-lens, non-film techniques you can do to affect exposure. Some of these include: BLOCKING ADDING INTENSIFYING MODIFYING Eliminating light sources completely or partially, like using flags to control light spill. Introducing new light sources or redirecting more light into a scene, like using flashes or bounce reflectors. Manipulating the amount of light, like using neutral density filters. Changing the apparent size and character of light, like diffusing it or concentrating it. More on lighting in the Lighting Basics Lunch & Learn.

Determining the right exposure

Exposure EXPOSURE MODES There’s three ways to determine exposure in a camera: AUTOMATIC Camera does everything for you. SEMI-AUTOMATIC MANUAL You control certain settings, and the camera determines the rest for you. You determine all of the settings. These can be selected using the camera’s mode dial

Automatic exposure AUTO Automatic exposure is determined using the camera’s built-in light meter, which measures the light that is reflected by a scene. The other automatic modes (in the example above: sports, portrait, night, landscape, macro), are an attempt to “set the camera in the right direction” in case AUTO by itself isn’t giving good results.

Semi-automatic exposure Av or A, Tv or S, P Semi-auto is often the mode of choice, since you get to input what matters for you (e.g. slow shutter), and the camera does the rest. It’s having your cake, and eating it too. • Av: Aperture Value, or Aperture Priority • Tv: Time Value, or Shutter Priority • P: Program, essentially AUTO but with exposure compensation

Auto and Semi-automatic exposure HOW DOES BUILT-IN METERING WORK??? Metering works by averaging the luminance determined by the metering mode and trying to approximate it to middle gray, or 18% gray. The most common selectable metering modes are: CENTER-WEIGHTED Evaluates 60-80% of the scene, feathered towards the edges. The default. PARTIAL or ZONES 10-15%, feathered, based on the camera’s focus zones or evaluative matrix. SPOT 1-5%, centered and feathered. Used when re-composing. AVERAGE Averages the luminance of the entire scene.

Manual exposure M or Manual Manual is used by purists and hobbyists, or when using older lighting equipment that can’t be synchronized with a camera. There’s two commonly used ways to determine exposure manually without using a built-in meter: • External Light Meters: Much more precise than camera built-in meters. Usually only used professionally, and generally outdated. • Histograms: Graphs that show the luminance distribution of an image.

Histograms DEFINED: Histograms show the frequency of pixels across a tonal range, from black to white absolutes. Histograms can be found in nearly all digital cameras (usually through the info button when previewing an image). They’re a great way to determine correct exposure, as well as the overall character of the image: • Key: Low-key, predominantly shadows; High-key, predominantly highlights. • Contrast: Low-contrast, a concentrated tonal range; Highcontrast, a spread out tonal range.

Histograms SHADOWS MIDTONES HIGHLIGHTS FREQUENCY (# pixels) 0 255 Each pixel in an 8-bit depth image is a combination of red, green, and blue values (RGB). Each of these colors can have a brightness value between 0 (black) and 255 (white). The histogram shows vertical bars that count the frequency of these values.

Histograms UNDEREXPOSURE Values are concentrated on the shadows, and blacks are clipped (dark tones are blocked up). “CORRECT” EXPOSURE Values are more distributed. Shadows and highlights taper off at the edges, with little to no clipping. (Because of the spread, it’s a high contrast image) OVEREXPOSURE Shadows are distributed across midtones and highlights, and whites are clipped (light tones are blown-out).

Exposure SETTING THE EXPOSURE SHUTTER SPEED (1/8000) Usually set through the main dial. APERTURE (f/5.6) Usually set through the control dial. ISO (6400) Usually set by pressing “ISO” button, then using the main dial.

Exposure Main dial, shutter speed Control dial, aperture

Some of the other stuff

Focal length DEFINED: Distance in mm from the optical center of the lens to the focal point when focused on a sensor. The focal length of a lens determines its angle of view. This determines how much the subject will be magnified. A lens with a focal length about equal to the diagonal size of the film or sensor format is known as a normal lens. Shorter focal lengths are called wide-angle, while longer focal lengths are called telephoto. Further, prime lenses have a fixed focal length, while zoom lenses have variable focal lengths (e.g. 24-105mm).

Focal length WIDE ANGLE NORMAL TELEPHOTO <20mm - 35mm ~50mm 80mm - >300mm

Focal length HOW DOES ANGLE OF VIEW WORK??? The angle of view gets wider the closer the optical center is to the sensor (creating a shorter focal length). A narrow angle of view, on the other hand, “crops” part of the image, magnifying it in the sensor. WIDE ANGLE OF VIEW SENSOR SHORT FOCAL LENGTH OPTICAL CENTER NARROW ANGLE OF VIEW SENSOR LONG FOCAL LENGTH OPTICAL CENTER

Focal length Consequences? Perspective distortion. If you’re framing a shot the same way with a wide angle and a telephoto (you move closer to your subject with the wide angle, move farther with the telephoto), perspective is significantly different in one and the other. Wide angles exaggerate or stretch perspective. Telephotos compress or flatten perspective.

Focal length WIDE ANGLE, STRETCHED PERSPECTIVE Wide angle stretches perspective, so objects are rendered progressively smaller the farther they are from the optical center. The distortion is also strongest the closer the object is to the optical center (giving it a fisheye effect). (Image was shot at 24mm, close to the subject) TELEPHOTO, FLATTENED PERSPECTIVE Telephoto flattens perspective. (Image was shot at 300mm, farther away from the subject)

Dynamic Ranges DEFINED: Dynamic range is the luminance range that a camera might be able to capture. It affects exposure in that certain scenes might have a large dynamic range that can’t be captured by a single exposure (like an interior shot with sunny windows in it), thus rendering certain areas of the image under or overexposed.

Dynamic Ranges INTERIOR EXPOSURE EXTERIOR EXPOSURE Exposing for the inside blows out the highlights from the outside. Exposing for the outside underexposes the entire interior. Decreasing window intensity using neutral density filters or waiting for a darker exterior would produce an acceptable exposure. Using flashes or strobes to light the inside of the room would produce an acceptable exposure. EXPOSURE COMPOSITE (HDR) Alternatively, multiple exposures (a “bracket”) can be combined to create a single image. High Dynamic Range (HDR) composites do this through automatic tone mapping, or it can be accomplished by using oldfashioned masking.

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