Chapter 5: Camera, the practical side

Aperture

• Opening at the front of a camera that admits light. It is usually circular, and except in very simple cameras is variable in size, so regulating the amount of light that passes through the lens to the film.

Effective aperture

• The diameter of the beam of light that passes through the outer lens component along its axis to the aperture

• it increases or decreases proportionally as the real aperture is varied

Relative aperture

• The ratio of the focal length of the lens to the effective aperture.

• If lens has a focal length of 50mm and the effective aperture is 25mm, the relative aperture is 50/25 = 2, which commonly expressed as f number

• Larger the f number, smaller the aperture.

• Usual sequence marked on the lens barrel is

• F2, F2.8, F4, F5.6, F8, F11, F16, F22, each “stop” marking a halving of the amount of light which the aperture admits.
• F2 --> F2,8 = one stop down
• F8 --> F4 = two stops up
  

Depth of field

• Zone of acceptable sharpness extending in front of and behind the point on the subject that is exactly focused by the lens.

• if you have an infinite depth of field, it means everything that falls into the photograph is in focus, for example, landscape photographs with wide angle.
• three ways to manipulate depth of field

1. the distance of the point focused from the lens (shorter the distance, the more shallow the depth of field)
2. the size of aperture (smaller the aperture, the greater the depth of field)
3. focal length of the lens (greater the focal length, the shallower the depth of field)

Shutter

• Mechanical device used to expose film to light for exact period of time.

Shutter speed

• The period of time that allows the camera to expose to light.

Film speed

• Degree of sensitivity of an emulsion expressed numerically for purpose of exposure calculation.

ISO

• International standards organization
• sensitivity of the film or the sensors.
  
• greater the ISO number, more sensitive it is to form images in the film, yet, grainier it is.
• ISO 100 and 200, good for daytime outdoor; ISO 400 and 800, good for nighttime or indoor, or when light is insufficient; ISO 1000 - 2000, good for high speed shooting.
  

Exposure

• total amount of light reaching the light sensitive material (film) or light sensors (digital camera)
• Overexposed = too bright, the image looks washed-out
• Underexposed = too dark