Photography Concepts, Understand Your Art

Originally posted 22 Jun 2010
Exposure is the amount of light allowed to fall on the photographic medium, the film or a digital image sensor. Exposure is measured in lux seconds or the measure of the intensity as perceived by the human eye. This interval on the photographic exposure scale is commonly referred to as a stop.

Focus is where light from object points is converged almost as much as possible in the image, sharp, and out of focus if light is not well converged, blurry. The border between these areas is called the circle of confusion.

Depth of field (DOF) is the portion of a scene that appears acceptably sharp in the image. A lens can only precisely focus at one distance and the decrease in sharpness is gradual on each side of the focused distance.

Shutter speed or the exposure time is the length of time a camera's shutter is open or can be thought of as the duration of light reaching the film or digital image sensor.

Slow shutter speed, moving objects blur.

Fast shutter speed movement is frozen.

Aperture is an opening through which light travels. The opening size determines the amount of light and the angle of that light over the digital image sensor. If an aperture is narrow (say f22), then sharp focus is achieved across the image plane. If an aperture is wide (f2.8) then a sharp focus is achieved for a certain focal length, part of the image plane is sharp around what the lens was focused on and blurred otherwise.

ISO is a light sensitivity measure and is the relationship between exposure and sensor data values that can be achieved by setting the signal gain of the digital sensor in a DSLR. The lightness of the finished image is measured by an exposure index rating similar to what would be obtained with film of the same rating at the same exposure. Digital Cameras far surpass film in terms of sensitivity to light and controlling image noise and film grain. Digital cameras have achieved ISO's up to 102,400, and you can commonly get acceptable results with ISO 3200 for good DSLR cameras which film speeds never got close to.

Perspective is a visual perception or the way in which objects appear to the eye based on their relative position to the viewer. As objects become more distant they appear smaller and as object gets further from the eye, its contrast with the background is reduced.

Composition is the placement or arrangement of visual elements or ingredients in a work or the organisation of the elements in an image according to the principles of art. Unity, Variety, Balance, Contrast, Proportion, Pattern

The rule of thirds is a compositional rule of thumb in which the rule states;

That an image should be imagined as divided into nine equal parts by two equally spaced horizontal lines and two equally spaced vertical lines.

The important compositional elements should be placed along these lines or their intersections as aligning a subject with these points creates tension, energy and interest.

For example an horizon should be at the horizontal line dividing the lower third of the photo from the upper two thirds and any important elements should be at the intersection of two lines. This is called a power point or a crash point. Depending on the composition you will find close enough to this rule can be enough to take advantage of the rule. Like all rules these are made to be broken so experiment.

To understand how you need to balance ISO, Shutter Speed, and Aperture to get a good exposure you would think that this is an equal mix of shutter speed, ISO speed, and aperture, but its not a simple as that. The problem is you can’t actually map what an exposure will be as any one or two of the other variables change. Composition, perspective and its relation to the rule of thirds is more of an artistic judgement.

If you understand all this and can exploit the relationship of these concepts and produce beautiful images, leave a comment tell me how.