A picture professionally shot will convey a message or concept. Professionals shoot in such a way that selected portions of photo is unsharp (blur). Normally viewers will stay away from blurred portions and keep their focus of attention on sharp portions of photo. Thus, photographers' decide what the viewers should see and how the photo is interpreted.
In this post, we will discuss about science of blur image formation. We have studied in our childhood, a convex lens will bend the rays. So, parallel (collimated) rays entering the convex lens will get bent and converge into a point. That point is called is 'focal point'. The distance between the centre of lens and the focal point is called 'focal length'.
In this post, we will discuss about science of blur image formation. We have studied in our childhood, a convex lens will bend the rays. So, parallel (collimated) rays entering the convex lens will get bent and converge into a point. That point is called is 'focal point'. The distance between the centre of lens and the focal point is called 'focal length'.
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| Figure 1. Science of Blur explaining through scenario |
Functioning of lens can be easily explained or understood, if we assume a scenario as depicted as Figure 1. In the scenario three subjects namely B-man, O-man and G-man (Green man) are standing one after another. B-man is very closer to the lens and G-man is far away from the lens. The light from the three men are falling on the convex lens. If there is no aperture then, rays emanating from B-man 'a' to 'z' would have fallen on the lens. But due to presence of aperture, part of the rays only enter into lens. Let us assume 50 mm lens (focal length) is used.
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| Figure 2. Different types of aperture sizes. Credit: Wikipedia |
The film or sensor array is placed on the focal point of O-man (The film is vertically rotated at 90 degrees). So, rays emanating from O-man are properly converged after traversing the lens and fall on the film. In the film a crisp and inverted O-man is seen. Now, let us take case of B-man and G-man. When the rays emanating from the B-man traverse the lens, the rays are converged after the film. So, on the film we see a circle instead of point. This is called 'circle of confusion'. That is why we see a blurred and inverted B-man in the film. Likewise, rays emanating from G-man traverse aperture-lens arrangement and converges before the film. Then slowly they start diverge and fall on the film. Due to this a circle is formed instead of point. Thus, we see a blurred and inverted G-man on the film.
O-man is moved little towards the lens or farther away from the lens will not affect the crispness of O-man in the film. If the O-man reaches near the G-man or B-man then image will become blurred. Quantum of distance, O-man can be moved without compromising the crispness is called 'Depth of field'. Normally aperture will be placed before the lens which controls the light falling on the lens. Aperture size and depth of field is indirectly correlated. A small aperture i.e. f/16 will yield deep depth of field (i.e. B-man, O-man and G-man will be crisp). A large aperture (in our case aperture f/2.8 is used) will create a shallow depth of field.
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O-man is moved little towards the lens or farther away from the lens will not affect the crispness of O-man in the film. If the O-man reaches near the G-man or B-man then image will become blurred. Quantum of distance, O-man can be moved without compromising the crispness is called 'Depth of field'. Normally aperture will be placed before the lens which controls the light falling on the lens. Aperture size and depth of field is indirectly correlated. A small aperture i.e. f/16 will yield deep depth of field (i.e. B-man, O-man and G-man will be crisp). A large aperture (in our case aperture f/2.8 is used) will create a shallow depth of field.
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This post is not giving a great piece of information. It is a 'remainder' which will help you unlock and understand any photography articles on ISO, shutter speed and aperture size. Lack of this information made my life deplorable for past two months.
