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  • Depth of field
  • Dslr

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Depth of field explained

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Digital photography jardon

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Depth of field

The distance at which a lens is focused is called the focal plane. All subjects exactly at this distance will be brought to sharp focus on the image sensor.

Subjects in front of, or behind the focal plane will be progressively rendered more and more out of focus. (see circle of confusion)

Eventually the point will be reached where the out of focus areas will be visually evident when viewing the final enlarged image.

These near and far sharpness limits define the depth of field.

Various factors determine whether this region is shallow (only subjects close to the focal plane are acceptably sharp) or deep (subjects from a long way either side of the focal plane are acceptably sharp)

These factors include

  • Aperture size
  • Degree of magnification
  • Image sensor size
  • Closeness of subject to the lens

For any given lens, aperture, focal length and image sensor size combination – there exists a focussing distance at which the depth of field is greatest – known as the hyperfocal distance – normally all image subjects from half this distance to infinity will be rendered acceptably sharp.

For a more detailed explanation see

Depth of field explained

Taking creative control of your photos

depth of field


Dslr– stands for Digital single lens reflex camera.

Digital (and film) reflex cameras enable the photographer to view the image that will be captured via an optical viewfinder. The image in the viewfinder being directed there via a mirror system mounted in front of the image sensor – hence the the term “reflex” as the view is a reflection from the mirror.

Dslrs are growing in popularity by photography enthusiasts as the technology develops and prices fall.

Outlined below are two lists of pros and cons – the first weighing the advantages / disadvantages of Dslr with traditional film cameras, and the second compares Dslrs with digital compact cameras.


Dslr vs Film slr


  • Cost per photo – once purchased a memory card may be used and then erased almost indefinitely dramatically reducing cost per photo compared to traditional film.
  • Instant review or even live preview – The image taken (or to be taken) can be instantly assessed on the camera's l.c.d display and therefore checked for exposure, composition and sharpness. Thus enabling the photographer to make appropriate adjustments to camera settings or composition prior to continuing.
  • Post process – Digital post process does not require a dark room or expensive and potentially hazardous chemicals. Far more photographers are therefore able to take control of the post processing of their images. (Although with a scanner, film negatives can also be processed digitally)
  • ISO Sensitivity – With a film camera the light sensitivity of the film (known as the “speed”) has to be predetermined and cannot be changed from one frame to the next within a roll of film. Dslrs enable a wide range of ISO sensitivity (nowadays to quite high levels at acceptable noise levels). Thus giving much greater flexibility over exposure control on a frame by frame basis – particularly relevent to low light photography without flash.


  • Format size – Generally the higher the format (ie film or sensor) size, the greater the potential for high image quality. The cost of production for large image sensors increases exponentially with size. The cost of “full frame” dslrs is therefore still prohibitive for most consumers, whilst true medium format digital cameras, although available, can typically cost tens of thousands of dollars! Having said this, for most photography enthusiasts, the image quality from modern dslrs acceptable.
  • Dust contamination – unlike with a film camera where any dust that gets into the camera body will almost certainly advance with the film and thus be cleared – with a digital camera there is the potential that dust contamination may actually stay on the image sensor and affect all subsequent shots. This is exacerbated by the fact that the electro static charge on the image sensor will actually attract dust. Most recent dslr models incorporate some form of sensor cleaning system to help deal with the problem and it is also possible to fix any blemishes during post processing.
  • Power supply. Digital cameras are dependant upon electric power from a battery – whereas mechanical film cameras have no such dependency.

Dslr vs compact camera


  • Image Quality - Having a larger image sensor size means image quality is generally higher – especially at higher ISO levels
  • Interchangeable lenses - The camera is not limited to having a fixed lens – meaning high quality lenses best suited to a specific purpose may be used.
  • D.o.f. - The larger image sensor enables greater control over depth of field – particularly for shallow depth of field effects favoured by portrait photographers.
  • Viewfinder - An optical viewfinder gives a clearer and more accurate view than an electronic viewfinder and enables a faster auto-focusing system to be used.
  • Response time - Often dslrs respond to the shutter button more rapidly and have faster burst rates for continuous shooting.


  • Cost - Generally higher cost – especially when the cost of the detachable lenses are taken into account – with these sometimes costing more than the camera itself.
  • Size – the mirror system and the longer focal length lens require the cameras to be physically more heavy and bulky which can result in the cameras being less convenient to carry – this can be a major issue for travel photography or when hiking long distances or when more discretion is desirable.
  • Dust - Dslrs have a greater tendency to dust getting on the sensor than compact cameras as the process of changing the detachable lens leaves the image sensor vulnerable to contamination.


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