Current webmaster: Shamim Pakzad (shamimp@ce.berkeley.edu).
CS 39J: The Art and Science of Photography is a freshman seminar taught
by Professor Brian A.
Barsky.
Site design by Steven Chan.
| CS 39J > Schedule & Notes > Session 3 Detailed Notes |
http://inst.eecs.berkeley.edu/~cs39j/session03.html
Notes from February 4:
When three-dimensional objects are represented in two-dimensional images, we use perspective to show distance, size and shape. Our perspective is our point of view, or vantage point.
From any certain place, the parallel lines of an object will appear to converge at a point called the "vanishing point". When this point is far away from the object in question, this object is likely far away. The parallel lines of an object hardly bend when the object is at a great distance. If the point appears to be close to the object, the object is likely closer. Parallel lines on close objects are bent. Close objects give a picture drama. This is preferable in most photography. However, in architectural photography the goal is to make the picture as faithful to the structure of the building as possible. In order to do this, remember that lines parallel to the picture plane remain parallel.
It is important to note that using a zoom lens does not give the same effect as moving the camera closer to an object. We can see this by comparing ratios. Say we are taking a photograph of a box that is one foot in all directions. If the distance from the camera to the front of the box is 10 feet, then the distance from the camera to the back of the box is 11 feet. That's a difference of 10%. If the distance from the camera to the front of the box is 100 feet, and therefore the distance from the camera to the back of the box 101 feet, that's a difference of only 1%.
Zooming in from a long distance will only have the effect of magnification - the perspective will still be that of an object from a distance. This perspective is incorrect and distorted, as the object will appear larger than it logically should, and makes the image flat. This can be effective in some instances, like when taking pictures of traffic. The cars will seem closer, and the traffic worse than it is.The human eye is used to seeing distorted perspective on a horizontal plane, but vertical convergence is often off-putting. A 45-50mm focal length lens on a 35mm film camera is "normal", not in the sense that it's the most common, but that it gives us the best representation on film of what we see with our eyes. (The fovea is the name given to the central part of the retina, which allows us to see in high-resolution. The low resolution in our peripheral vision is a function of the macula.)
A wide-angle lens is typically 24mm or 28mm (a smaller number than 35). It provides us with an enormous depth of field. A telephoto lens has a length larger than 50mm. The higher the number, the less depth of field.
F-stop, which controls depth of field, is the fraction where focal length is the numerator and aperture (diameter) is the denominator.
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