DSLR camera anatomy

DSLR Anatomy

exposure

  • influenced simultaneously by
    • ISO - sensor light sensitivity (film speed)
    • shutter speed - expressed in fractions of seconds
    • aperture opening - lens aperture opening

exposure

sensor and exposure

  • larger the sensor area, more the light captured by the sensor
    • more exposure obtained by a bigger sensor for a given scene

Sensor Formats

  • for APS-C, 20 Mega Pixel is max for spatial resolution usable by almost perfect lens
    • for full frame, 54 MP

Sensor Size and Exposure

dynamic range of sensor

  • the range between the brightest and the darkest lights that can be registered without noise

  • specified in terms of ISO sensitivity range

    • characteristic of a given camera sensor specification
    • i.e. ISO 64000 implies highest sensitivity is 64000 and lowest is 0
    • usable ISO varies from camera to camera

ISO and noise

  • as the ISO increases,
    • along with light sensitivity,
    • noise induced by sensor also increases

Imgur

shutter

  • shutter opening and closing is what sets the time for image registration
    • this time span is the exposure time for the image
    • digital cameras store the image on to the storage disk, while film cameras expose the film to incoming light for this duration
  • shutter speed, expressed in fractions of seconds, sets the speed of the opening and closing
    • smaller fractions of time means the exposure of the sensor to light is less
    • larger fractions of time means longer exposure

shutter and blurring

  • for a given subject and scene, if the shutter isn’t fast enough to open and close
    • there will be blurring in the image obtained
  • shutter speed has to be balanced to get sufficient exposure but avoid blurring in the scene
    • unless blurring is used artistically

Imgur

rules of thumb

  • 1/60 second exposure for a static shot
    • 1/1000 for sports shots
  • longer the 1 minute of exposure for twilight waterscape scene for blurry water
  • 15 min + for a night photography or astrophotography shot

lens

  • before jumping into aperture it is necessary to talk about lenses
  • lenses help focus the light coming into the camera enclosure on to the sensor plane
  • lenses allow focus to be adjusted on different parts of the scene
    • there is a plane of focus along with a depth on either side of the plane
    • where objects are sharp and the rest is out of focus and hazy
  • for cameras that allow interchangeable lenses, the lenses are a separate fitting that gets seated in front of the mirror sensor assembly

lens types

  • lenses are of two types
    • fixed focal length or prime lenses
    • variable focal length or range lenses

focal length and COV relationship

Imgur

focal length and DOF relationship

  • as the focal length of lenses decreases, the maximum depth of field allowed by the lens increases
    • i.e. 8 mm lenses have more depth of field at max aperture opening compared to 70 mm lenses

Imgur

aperture

  • aperture ring is a part of the lens
    • usually cameras which allow interchangeable lens allow working with lenses of different aperture opening ranges
  • the amount of light let in by aperture opening of a given diameter is expressed in terms of f-number or f-stops
    • f-number = focal length of lens ÷ diameter of aperture opening
    • smaller the f-number, more the light allowed

aperture and depth of field

  • more open the aperture is, flatter the depth of field around the plane of focus
    • more open apertures i.e. flatter depths of fields can be used to obtain effects like bokeh
    • where as deeper depths can be used for landscape, seascape and astrophotography

Imgur

exposure summary

  • higher the ISO, more the exposure, trade off is more noise
  • longer the shutter speed, more the exposure, trade off is more blurring
  • more the aperture opening, more the exposure, trade off is loss of depth of field

further reading