Exposure Controls - DSLR 1

Exposure controls Tuesday, September 6, 2011

Dharamsala DSLR Workshop 1 1

Exposure controls outline * Aperture * Shutter speed * ISO * Light meter * Metering modes * Exposure modes * Focal length Photo by Umberto Salvagnin

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The amount of light that passes through the camera to the sensor is controlled by the aperture and shutter speed.

Both aperture and the shutter speed work in units of light called stops.

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Aperture The aperture is a circular opening inside the lens that allows light to enter the camera.

The wider the aperture diameter (like f/2), the more light enters the camera and allows for less depth of field and more background blur in the photo, therefore, there will be less objects in focus.

The smaller the aperture diameter (like f/27), the less light enters the camera and allows for more depth of field, therefore, more objects in the frame will be in focus.

The range of aperture setting is indicated by a series of numbers called f stops. An average aperture scale ranges from f.2 to f.27. The wider the aperture, the smaller the f stop number and the smaller the aperture, the greater the f stop number will be.

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Photo Š Jonathan Kos-Read Taken on a Nikon D700 / Shutter speed 1/400/ Aperture f/1.4 / ISO 250 Tuesday, September 6, 2011

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Photo Š Jonathan Kos-Read Taken on a Nikon D90 / Shutter speed 1/60/ Aperture f/1.4 / ISO 800 Tuesday, September 6, 2011

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Photo by Vinoth Chandar Taken on a Canon EOS 5D Mark II / Shutter speed 1/100 / Aperture f/22 / ISO 100 Tuesday, September 6, 2011

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Photo by Fasal AlKhudairy Taken on a Canon 7D / Shutter speed 8/ Aperture f/22 / ISO 100 Tuesday, September 6, 2011

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Shutter speed Shutter speed regulates the amount of time the light passes through the camera to reach the sensor.

A slower shutter speed (like 1/25, used in low light) allows more light to reach the sensor, whereas a faster shutter (like 1/400, used in brighter light) speed allows less light.

Shutter speeds that look like this on the control panel: 30 45 60 stand for 1/30th, 1/45th, 1/60th of a second until 1/4000th of one second. Shutter speeds that look like this: 1� 2� 3� stand for 1-second, 2-second, 3seconds and so on until 30-seconds.

B stands for Bulb, which means the shutter will remain open for as long as the shutter release button is held down.

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Shutter speeds examples

1/400 1/400th of one second

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1/100 1/100th of one second

1/25 1/15th of one second

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Photo by Nathan Hayag Taken on a Sony DSLR-A700 / Shutter speed: 1 second / Aperture f13 / ISO 100 Tuesday, September 6, 2011

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Photo by Paul Bica Taken on an E-2 / Shutter speed: 8 seconds / Aperture f/2.8 / ISO 100 Tuesday, September 6, 2011

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Photo by Sean McGarth Taken on a Nikon D80 / Shutter speed: 30 seconds / Aperture f8 / ISO 100 Tuesday, September 6, 2011

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Photo by Rob Nunn Taken on a Fujifilm FinePix S5700 S700 Shutter speed 1/1000 (0.001 sec) Aperture f/6.3 ISO 100 Tuesday, September 6, 2011

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Photo by Rama V. Taken on a Sony DSC-H7 / Shutter speed 1/4000 sec / Aperture f/8 / ISO 100 Tuesday, September 6, 2011

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The relationship between aperture & shutter speed As aperture and shutter speed are both measured in stops of light, they stand in a reciprocal relationship: the sensor can be exposed by a wide aperture for a short amount of time or by a narrow aperture for a longer period of time. For example, the following combinations of aperture setting and shutter speeds will produce exactly the same exposure.

Aperture

f.4

f.5.6

f.8

f.11

f.16

Shutter speed

1/250

1/125

1/60

1/30

1/15

Imagine a tap controlling water flowing into a bucket.

You can fill the bucket with water either by opening the tap to its widest for a short time OR by letting the water drip in the bucket slowly over a longer time.

In a similar way, film can be exposed in a camera either by a wide aperture for a short time at a fast shutter speed OR by a narrow aperture for a longer time at a slower shutter speed.

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How to hold your SLR camera and avoid camera shake

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How to avoid camera shake: the reciprocal rule Camera shake is one of the most common causes of blurry or out of focus photos. Fortunately, you can avoid camera shake by learning how to hold your camera and by following one basic rule of photography: the reciprocal rule.

The reciprocal rule is based on the fact that at slower shutter speeds, any slight camera movement will cause motion blur in your photo. Therefore, the opposite is also true, that the faster the shutter speed, the sharper your images are likely to be.

The reciprocal rule states that when you’re hand holding your camera, your shutter speed should NOT be lower than the reciprocal of your lens’ effective focal length.

For example, if you lens is 100mm, then your shutter speed should not be any lower than 1/100 of a second. So the basic formula is:

Shutter speed = 1/focal length When using the reciprocal rule it is important to remember that you need to know the equivalent focal length of your lens, therefore the crop factor of your camera comes into play. For example if you have your zoom lens set to 200mm and your camera’s crop factor is 1.5 (typical for an APS-C image sensor) then your equivalent focal length is 300mm and your shutter speed should be kept at 1/300 of second or faster for the sharpest pictures.

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ISO ISO refers to the sensitivity of the sensor to light.

The higher the ISO, the more sensitive the sensor is, but the more likely “noise” (random bright pixels) occurs.

A higher ISO can be used in low light and dim settings (as seen below in the third photo) as it captures available light and at times can be used in place of flash photography.

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To avoid unnecessary “noise” and for sharper images, use ISO 100-400 when you can, especially in sunny, outdoors settings where there is plenty of light.

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Light meter The light meter is a built-in device in the the camera body that measures how much light is needed to correctly expose your sensor in a specific situation.

The light meter takes into account your ISO in aperture and shutter speed and tells you how much light you will need to expose your image correctly. This method of measuring light is called TTL (through the lens) metering.

To take a light reading, simply point your lens at a subject and activate the light meter by gently pressing the shutter release button halfway down.

The light meters is from -2 to +2 stops. Change your aperture, shutter, or ISO so have the meter on 0 for the correct exposure.

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Assessing exposure Despite the sophisticated nature of modern light meters, they are not infallible. Your light meter can only measure the amount of light that is projected into its photo-sensitive cell. To achieve the best possible exposure, you need to understand how your light meter works.

Your light meter will give you only the average reading of a scene and produces an overall tone that is equal to mid-grey. In color photography, mid-grey would be equal to a tone of any color that is halfway btween the lightest and darkest tone of that color.

Over-exposure, letting in too much light than recommended by the light meter will result in a photograph that is too light (as in +2EV below) while under exposure, letting in less light than recommended results in a photograph that is too dark (as in -2EV below).

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EXPOSURE: against bright backgrounds If you take a light meter reading with a very bright background, the background will dominate the reading and the subject will be under-exposed.

Move in close to the subject and take a reading of the most important tonal area.

This will result in the background being over-exposed, but the subject, which is the most important element of the picture, will be exposed correctly.

Photo by Nattu

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EXPOSURE: against dark backgrounds If you take a general light meter reading of the a scene with a dark background, this reading would result in your subject in front of the dark background being over-exposed.

To avoid this, move in close to the subject and take a reading of the most important tonal area.

Photo by Claude Renualt

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EXPOSURE: high contrast lighting conditions In a high contrast scene with an extreme range of light intensities, you can expose for the dark areas and allow the bright areas to record as very light, or vise versa, as seen in this photograph where the photographer has chosen to expose the railroad and keep the subject backlit to contrast against the light.

Photo by Thomas Leuthard

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Metering modes Metering modes allow you to manipulate the light meter’s reading by concentrating it on the entire subject, part of the subject or a small fraction of the subject.

Evaluate (Canon), Matrix (Nikon) This is the most advanced metering system.

It divides the frames into different zones and reads the light in each zone. The meter evaluates all these readings and determines the right exposure. This is mode is a useful “all-purpose� mode.

Center weighed average (Canon & Nikon) The meter measures the entire frame but concentrates most of its sensitivity on the center of the frame. This is useful when you want to base your exposure on a specific area in the frame.

Spot/Partial (Canon & Nikon) The meter concentrates on a small area of the frame. This is used for a very selective exposure and requires experience.

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Metering mode examples

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Exposure modes (Canon) The exposure mode determines which combination of aperture and shutter speed can be set.

The exposure modes to the right are for Canon cameras.

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Exposure modes (Nikon) Canon

Nikon

P Programmed Autoexposure (same for Canon) Camera selects both the f-stop and shutter speed to ensure proper exposure but the user can choose from multiple combinations of the two settings

A Aperture-priority (Av for Canon) The user selects f-stops and the camera selects the shutter speed that will produce a good exposure

S Aperture-priority (Tv for Canon) The user sets the shutter speed and the camera selects the fstop that will product a good exposure

M Manual Exposure (same for Canon) The user selects f-stops and the camera selects the shutter speed and f-stop

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Focal length

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Types of lenses

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