Understanding Exposure Exposure. Defined Some scenes are brighter than others so the camera needs to control how much light reaches the film/chip Too little light – the image will be too dark Too much light – appears washed out
Understanding Exposure Controlling Exposure Two ways to control exposure in exact, measured amounts are via the aperture and shutter speeds The aperture controls how much light enters the lens and the shutter speed controls the length of time the light strikes the film
Understanding Exposure Controlling Exposure Photographers use the terms stopping down and opening up to describe what happens when they change the amount of light reaching the film. Decreasing the exposure is to “stop down” while an increase in exposure would be to “open up”
Understanding Exposure Apertures The aperture is the bladed diaphram inside the lens that opens or closes to control the amount of light entering the camera. f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f,22, f/32, f/45, f/64 An f-stop refers to the size of the aperture. The higher the number, the smaller the opening. This is because all f-stop numbers are actually fractions so an f-stop of f/2 can be thought of as 1/2 of fully open and an f- stop of f/8 is 1/8th the opening diameter
Understanding Exposure Aperture cont… Apertures have been standardized so that each stop either doubles or halves the amount of light reaching the film An f-stop of f/2 lets more light in than f/8
Understanding Exposure Apertures cont…depth of field As the aperture is stopped down and gets smaller, more of the background and foreground in the scene becomes sharp. The area of acceptable sharpness in a scene is known as the depth of field.
Understanding Exposure Apertures cont… Wide apertures Throw backgrounds out of focus Essential in low light situations Also known as fast apertures Maximum apertures vary between lenses and not all lenses have the same apertures available
Understanding Exposure Apertures cont…Mid-Range Apertures • Tend to give the highest resolution picturesSmall Apertures • Essential in very bright conditions • When increased depth of field is desired • Small apertures have large f/numbers
Understanding Exposure Shutter Speeds The shutter of a camera can be thought of as a door that opens and closes extremely quickly. It is actually closer to a curtain, but the principle is the same. How long the curtain remains open is the shutter speed.
Understanding Exposures Shutter Speeds cont… Like apertures, the shutter speeds have been standardized and each successive change in the shutter speed is equal. If you move up the scale such as from 1/4 sec to 1/8 sec or from 1/125 sec to 1/250 sec, you double the speed and half the light transmitted (stopping down). Conversely if you move from 1/60 sec to 1/30 sec (open up) you half the speed and double the amount of light
Understanding Exposure Remember the same having/doubling principle is at work with apertures. If you switch from f/8 to f/11, you will have “stopped down” one stop allowing only half the light to reach the film plain What exists is a series of equal steps of change in the amount of light reaching the film by either the shutter speed or aperture
Understanding ExposuresRelationship between apertures and shutter speeds
Understanding Exposure Camera Shake Camera shake occurs when too slow a shutter speed has been selected for handholding capabilities. The image becomes blurred and sharpness is lost. A general rule is to select a shutter speed at least equal to the focal length you are using. A 50mm focal length would require a shutter speed of 1/60 sec to avoid camera shake A focal length of 200mm would require 1/250 sec shutter speed