1/4/11 – Tuessday’s Photo Tutorial

From our summer trip, June - July 2010


Here is the first in a series of photographic tutorials and tips that I intend on posting here each Tuesday.  Hope you enjoy and share them.

Photographic Exposure Basics

Photography is a method and the art of capturing light on a light sensitive surface. The skilled photographer understands the various ways to set their camera to record the light in order to express his or her creative vision. Understanding photographic exposure basics will allow you to adjust your camera settings to capture the scene. Remember the camera is simply a tool the photographer uses to express their creative vision. (This post is an overview of photographic exposure basics. For each of the following three weeks I’ll post more specific details on the 3 camera settings discussed here.) The three main camera settings for controlling exposure are:
• Shutter Speed
• Aperture
• Sensor ISO (Film Speed)

A thorough understanding of each of these settings and how they affect final image quality, (whether for screen or print), is foundational knowledge for any photographer; novice, advanced, or professional.  Artistically, there is no right or wrong combination for any image. Successful exposure requires knowing what settings to use for the image you wish to create. Proper exposure is achieved with various combinations of ISO, shutter speed, and aperture. Understanding how each of these settings interacts with the others will help the photographer create properly exposed images.

Sensor ISO (ISO)
ISO is the light sensitivity of a film or equivalent digital sensor sensitivity. The larger the number the less light is needed to capture the image. ISO is almost always the first setting determined. With film cameras, the film speed is determined by what film you load. In digital cameras, the photographer chooses the ISO to use in a given situation. The chosen ISO tells the camera how much light the sensor needs to record an image. Normally, the brighter the ambient or natural light, the lower, (or slower) the ISO setting. As the ambient light darkens the ISO should be higher (or faster).

Aperture can be one quite confusing for many new photographers. But it doesn’t need to be. Simply put aperture is an adjustable opening inside the camera lens that works like the iris of our eyes. (Aperture size also affects depth of field (DoF), but I’ll save details of aperture’s affect on DoF for next week’s tutorial. (1/11/11).

Aperture works in conjunction with shutter speed and ISO to control the amount of light recorded on the sensor. Remember aperture is like our eyes, in dim light it opens wide to allow more light through. In bright light the aperture closes to allow less light through.

Aperture is measured in F-Stops. F-Stop numbers get bigger as the aperture gets smaller. Closing the aperture, (or stopping down) or increasing F-Stop number cuts in half the amount of light reaching the film.

Shutter Speed
Shutter speed controls the amount of time that your film, or digital sensor, is exposed to light. The shutter is opened when you press your camera’s shutter release. Shutter speed determines how long
the shutter remains open. Shutter speed is generally measured in seconds or fractions of a second. A shutter speed of “5000” means that the shutter will open for 1/5000th of a second. Shutter speeds of 1 second and longer are often marked to avoid confusion. Refer to your camera’s manual for specific details. The letter “B” or “Bulb” is used to keep the shutter open as long as the shutter release button is held.

Some General Exposure Rules of Thumb:
Sunny f/16 Rule
Sunny f/16 rule is a method of determining daylight exposures without a light meter. The basic rule is, “On a sunny day set aperture to f/16 and shutter speed to the [reciprocal of the] ISO film speed [or ISO setting] for a subject in direct sunlight.” For example:
• On a sunny day with ISO 100, set the aperture to f/16 and the shutter speed to 1/100 or 1/125 second (on many cameras 1/125 second is the available setting nearest to 1/100 second).
• On a sunny day with ISO 200 set the aperture to f/16, set shutter speed to 1/200 or 1/250.
• On a sunny day with ISO 400 set the aperture at f/16, set shutter speed to 1/400 or 1/500.

Shutter Speed for Hand-Held Photography
A general method of determining the slowest shutter speed to use for hand-held, (i.e. without a tripod) photography is to use the focal length of the selected lens. For example, if you’re shooting with a 70-200mm zoom, and the lens is zoomed to 100mm, you should use shutter speeds of 1/100 of a second and faster. This will help eliminate camera shake and the resultant “fuzzy” or “soft” pictures.

Exposure Slide Rule

When I began serious photography, I had a Kodak Exposure Slide rule that I carried in my camera bag. As I got more familiar with these principles I was able to compute exposure equivalencies on the fly. A Simple exposure slide rule can be printed out and assembled following the directions at the link here: http://squit.co.uk/photo/files/ExposureCalculator.pdf


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