Exposure And Depth Of Field

In photography, exposure refers to the amount of light that penetrates through a photographic film at a given time. The amount of light exposure of the film depends upon factors like shutter speed, lens aperture, etc. Thus, , when the shutter cycle is long the photographic film is exposed to a source of light for a longer duration. On the other hand, when the shutter cycle is brief, speedier and recurrent in nature it results in multiple exposure of the photographic film or image sensor within a given time.

Nagahara describes the depth of field as range of scene depths within an image distance that appear focused. Hence, among the factors that determine the amount of sharpness and blurriness of all the objects in a particular scene include the type of camera that is being used, aperture speed and distance of the objects from the lens.

In photography, both exposure and depth of field are determined by the aperture and shutter speed. This shows that they are correlated in some way or the other. The purpose of this work will be to find it out with the help of scholarly researches.

In general, the objects that are present in a single image are placed at different distances from the camera lens. This results in gradual blurring of the farthest object. Shan and Agarwal conducted a research to find out how high quality motion de-blurring can be achieved from a single image. The researchers computed a de-blurred image with the help of an amalgamated probabilistic model for  blur kernel evaluation as well as restoration of unblurred image. The camera aperture was set to disallow long shutter speed so that the photographic film gets minimal light exposure. This resulted in de-blurring of a number of objects in a single image and making them appear as if they are all within the same depth of field from the lens. Another experiment was conducted to achieve motion deblurring with the help of fluttered shutter. This experiment also suggested that in conventional photography, single exposure of the aperture leads to motion blurred photographic image of moving objects. Therefore, the researchers calibrated the situation by fluttering the camera’s shutter open and close within an exposure time. Consequently, they found that motion blur effect was removed and the image gave a virtual feeling that all the objects are placed at the same depth of field.

To conclude, it can be said that depth of field is the span of distance between the nearest and the farthest object in a focal range where the zone of sharpness is within the acceptable limit. Thus, by determining the exposure of lens to the light source a photographer can generate a virtual feeling that the depth of field of various objects located within a single scene has been changed.


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