Techniques and Practice - Week 2 - Getting to know your DSLR

Getting to know your DSLR

Exposure

Exposure is the total amount of light allowed to fall on the camera's sensor as the photograph is made. The more light that hits the sensor, the brighter the image will be.

Exposure can be broken down into - shutter speed ( the time for which light is let through to the sensor), aperture (how much light is let through to the sensor) and ISO (the sensitivity of the sensor).

Shutter speed

Light is allowed to pass through the camera and onto the sensor by opening a shutter inside the camera for a moment.  How long this shutter is opened determines how much light passes through and hence how light or dark the image will be.  This is known as the shutter speed.

 

 

Aperture

You can change the amount of light passing into the camera by adjusting the size of the hole that the light comes through. The hole is known as the aperture which is called the f-stop.

Decreasing the size of the aperture by one stop halves the amount of light coming through it.

The sizes of aperture available, depends on the lens that is attached to the camera.

Physically large apertures have small f-numbers e.g.  f/2.8  f/4  f/5.6, while small apertures have large f-numbers e.g. f/16 f/22 f/32.

Each f stop lets in half the amount of light as the previous one.  You need to lengthen the shutter speed by exactly one stop in order to get the same amount of light through to the sensor and achieve the same brightness in a photograph.

 

 

 

ISO Sensitivity 

Altering the camera's sensitivity changes the amplifiers that magnify the signal as it comes off the sensor.  Doubling in ISO value means the sensor is now twice as sensitive to light as it was.

 

A typical scale

 

 

 

 



As the ISO  value increases so the picture quality worsens, with what is know as digital noise being evident in a photograph.  Noise is always there, but it is exacerbated by a higher ISO setting.

 

 

Putting everything together

 

Shutter speed, aperture and ISO have all been designed to work together.  By varying each by a stop, the amount of light entering the camera is either doubled or halved or the sensitivity of the sensor is doubled or halved.  This means that opening the lens aperture from f/8 to f/5.6 has the same effect on the brightness of a picture as lengthening a camera's shutter speed from 1/250 to 1/125 seconds.  Both actions let in twice as much light.

 

Likewise, lengthening the shutter speed while closing down the aperture by the same amount of stops will have no net effect on the brightness of the picture. 

 

 

Creativity in the studio

 

 

Low Key Lighting

 

 

You need a single light source and a dark or black backdrop, a reflector can be helpful.

 

Low key photography is when you take a photograph of a subject where everything except the subject is dark.

 

The ambient light should be as low as possible.  Low key light accentuates the contours of an object by throwing areas into shade while a fill light or reflector may illuminate the shadow areas to control the contrast.

 

 

 

 

Properties Canon EOS 7D

                  F Stop              f/5.6

                  Exposure time 1/25 sec

                  ISO Speed        100

                  Focal length     50mm         

 

 





Low key lighting photography relies on shadows, deep black and darker tones. Its usually sombre, mysterious and moody, dramatic or even ominous depending on the subject.  They tend to have a lot of contrast, with primary impact coming from the shadows.