Camera LENSES, APERTURE AND DEPTH OF FIELD

Camera LensesWide angle lenses distort the image so that extreme wide angle can look like its convex such as a 15mm or 8mm.

With a wide lens most of the image will be in focus and you will have a deep or large depth of field.

Perspective is also lengthened and so images look like they are further away than they actually are.

Camera lensesTelephoto or long lenses have the opposite effect to a wide angle lens.

The foreshorten the image so that objects in the distance look closer than they are and perspective is condensed.

You have a much greater depth of field with a long lens and much of the image can be blurry. This give the sense of an object ‘popping out’ from the frame.

Camera sensors Digital cameras record onto a sensor. This replicates the function of film stock in film cameras. The size of the image sensor has a bearing on the image that the camera produces. A full frame image sensor is equivalent to 35mm film and it captures the largest area. Smaller sensors capture less subject area and in order to achieve the same frame need to be blown up to size. This means that less information is captured and hence the image quality is less. Sensor size also has an effect on dynamic range. Dynamic range is the difference between the maximum and minimum measurable light intensity i.e. white and black.

Crop factor Putting a lens designed for a full frame camera produces a crop factor.

The crop factor is a ratio of about 1.5. This means that when using a camera with a smaller sensor such as the canon APS-C with a full frame lens such as a 28mm the image at the side will be lost and to compensate the camera will produce a zoom effect giving a look more like a 45mm lens.

To compensate for this lenses designed for crop sensors will often go wider to about 18mm in order to achieve the same effect as a 28mm on a full frame.

Aperture and Depth of Field.

Aperture and Focal Length on DOF

Focal Distance and Wide Lenses

You can achieve a shallow depth of field with a wide angle lens if you position your camera very close to the subject and open up your aperture.