Camera Controls Metering & Basic Exposure By Wayne Littlewood For Carrick Camera Club
Metering • In a nutshell, exposure metering is the means of telling the camera how much light will expose the digital sensor (or film). • Too little light means underexposed with loss of shadow detail while too much light means overexposed and blown out highlights.
Metering • The simple thing that your camera tries to do is to achieve an exposure level that is referred to as Middle grey (aka 18% Grey). The idea is that if the sensor (or film) is metered to middle grey, the rest will fall into place and be properly exposed. • In the metering process, Your camera looks at the scene, checks how much various areas of the frame are lit and decides how much total exposure (total light) is required to create the picture such that it is equivalent to middle grey shade.
Metering • There are two general types of light meters: One measures reflected-light and the other measures incident-light. • Reflected-light meters measure the light reflected by the scene to be photographed. • All in-camera meters are reflected-light meters. • Incident-light meters measures the amount of light falling on the subject Taking an incidentlight reading requires placing the meter at the subject's position and pointing it in the general direction of the camera.
Metering • Most Camera’s will have 3 metering modes. • Evaluative (aka Pattern or Matrix) • Centre Weighted Average • Spot
Metering Evaluative Metering: • The Camera divides the scene into several zones and does calculations to come up with the right exposure. • The Camera gives equal importance to the entire scene to make sure that over all the best exposure is achieved in the entire scene.
Metering Centre Weighted Metering: • This is similar to the Evaluative Metering, except that instead of giving equal importance to all areas, the Camera gives higher importance to centre of the image. • The camera tries to make sure that the centre is properly exposed and may compromise the rest of the image, (i.e. underexpose or overexpose)
Metering Spot Metering: • Spot metering allows you to meter the subject in the centre of the frame. Only a small area of the whole frame is metered and the exposure of the rest of the frame is ignored. • This type of metering is useful for brightly backlit, macro, and moon shots.
Metering • In manual mode, you are selecting everything, (Aperture, Shutter & ISO) so you are not really using camera's metering capabilities inherently. However that does not mean it becomes unavailable. • Most cameras show some form of indicator regarding how you are doing based on your selected parameters. • It may show you, how many stops above or below you are with respect to the cameras metering. You don't have to use it, but it's there for reference.
Basic Exposure • Exposure - The total amount of light allowed to fall on the digital sensor (or film) during the taking of a photograph.
Elements governing exposure Aperture
Exposure Triangle Shutter Speed
ISO Next
Aperture • What is aperture? - the opening at the rear of a lens through which the light passes, a diaphragm controls the amount of light that can reach the sensor (or film).
Aperture • Aperture is measured in terms of f stops. Each f stop represents a doubling or halving of the light reaching the sensor (or film).
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Aperture • The f number represents the constant ratio between the focal length of the lens and the diameter of the hole that lets the light through. • The smaller the f number (i.e. f2.8) the larger the aperture and therefore the more light that is passing to the sensor. • The larger the f number (i.e. f22) the smaller the aperture and therefore the less light that is passing to the sensor.
Aperture • A creative byproduct of aperture is depth of field (the plane of sharp focus in an image). • In Aperture priority you control the Depth of Field (DoF) and the camera selects the appropriate shutter speed to achieve the correct exposure.
The smaller the f number the shallower the DoF
The larger the f number the greater the DoF
Aperture • Aperture Priority is favoured by Landscape photographers, Portrait photographers, Macro Photographers.
Shutter • What is A Shutter / Shutter Speed? • A shutter is a device that allows light to pass through to the sensor for a period of time. • Shutter speed is the measure of time that the shutter remains open, typicialy measured in fractions of a second.
Shutter • Common Shutter Speeds • Each Stop represents a doubling or halving of the light reaching the sensor 1
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Shutter • When considering what shutter speed to use in an image you should always ask yourself whether anything in your scene is moving and how you’d like to capture that movement. • If there is movement in your scene you have the choice of either freezing the movement (so it looks still) or letting the moving object intentionally blur (giving it a sense of movement).
Fast Shutter Speed – Freezes motion (1/2000th second)
Slow Shutter Speed – Shows motion (1 second)
Shutter • In Shutter Priority you control the speed of the shutter and the camera will select the appropriate aperture to achieve the correct exposure. • Shutter speed “rule of thumb”, choose a shutter speed that is larger than the focal length of the lens, e.g. if you have a 50mm lens then 1/60th second is probably ok but if you have a 200mm lens you’ll probably want to shoot at around 1/250th second. • Shutter priority is often used by Sports Photographers, Photo-Journalists.
ISO • What is ISO? - ISO is the measure of a sensors (or film) sensitivity to light. • The lower the ISO (e.g. ISO 100) the lower the sensitivity to light & the longer the exposure required. The lower the ISO the finer the grain which results in a more crisp image. • The higher the ISO (e.g. ISO 1600) the higher the sensitivity to light & the shorter the exposure required. The higher the ISO the more coarse the grain.
ISO • Higher ISO is typicaly used under low lighting conditions. • The trade off for using higher ISO is digital noise / graining. • With ISO set to “Auto” the camera will determine the appropriate “ISO” based on the shooting contidions. It will try keep the ISO as low as possible
ISO • Common ISO Stops • Each Stop represents a doubling or halving of the light reaching the sensor
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Exposure Summary • Remember that thinking about one element in isolation from the other two elements of the Exposure Triangle is not really a good idea, e.g. Shutter speed in isolation from Aperture and ISO for as you change shutter speed you’ll need to change one or both of the other elements to compensate for it. • Example: if you speed up your shutter speed one stop (for example from 1/125th to 1/250th) you’re effectively letting half as much light into your camera. To compensate for this you’ll probably need to increase your aperture one stop (for example from f11 to f8). The other alternative would be to choose a faster ISO rating (you might want to move from ISO 200 to ISO 400 for example).
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