1. clarification: Focal and length and depth of field
1.1. telephoto lenses=shallower depth of field
1.1.1. b/c they are used to magnify the subject when on is unable to get closer
1.2. if occupies same fraction of image for both telephoto and wide angle lens the total DOF is constant with focal point
1.2.1. require to get closer with wide angle lens or further with a telephoto lens
1.2.2. ex. focal length: 10, focal distance: 0.5, depth of field: 0.482; focal length: 20, focal distance: 1.0, depth of field: 0.421
1.3. longer focal lengths= shallower depth field b/c the backround is enlarged relative to the foreground.
1.3.1. cause an out of focus backround look more out of focus b/c its blur has become enlarged.
1.4. for a more representative of everyday use us standing in the same place and focusing on a subject at the same distance, a longer focal length will have a shallower depth of field.
1.4.1. effect due to higher magnification, not focal length
2. based on when the circle of confusion becomes larger than the size of your camera
3. shallower for SLR cameras then for compact digital cameras b/c it requires a longer focal length to achieve the same field of view
4. calculation depth of field
4.1. decide an appropriate value for the maximum allowable COC
4.1.1. based on both camera type and on the viewing distance/print size combination
5. Depth of Focus&Aperture Visualization
5.1. concept of depth of focus
5.1.1. "focus spread"
5.2. differs that it describes the distance over which light is focused at the cameras sensor, as opposed to the subject
5.3. when object is focused, light rays originating from that point converge at a point on a camera's sensor
5.3.1. if light rays hit sensor at a slightly diff location, the object will be rendered as out of focus and increasingly so depending on how far apart the light rays are
6. range of distance that appears accepblity sharp
6.1. varies on camera type, aperture , and focus distance.
6.2. gradual transition
7. Circle of Confusion
7.1. how much a point needs to be blurred in order to be perceived as unsharp.
7.2. if exaggeration for clarity; tiny fraction of the camera sensor
7.3. when perceptible to our eyes is so not "acceptibly sharp anymore
7.4. unnoticeable at times when enlarged 8time10 inch print and observed from a standard viewing distance of about 1 foot.
7.4.1. circle of confusion is negligible of no larger than 0.01 in.
7.5. diff maximum applies for each size and viewing distance combos
7.6. depth of field only sets a maximum value for the COC, and doesnt describe what happends to regions once they become out of focus
7.6.1. regions called "BOKEH" from japanese
7.6.2. two images with identical depth of field may have diff bokeh, depending on the shape of the lends diaphram
7.7. not a real circle but is approximated when it is super small
7.7.1. when it enlarges, most lenses will have a polygonal shape with 5-8 sides
8. controlling Depth of field
8.1. aperture and focal distance=determinig how bog the circle of confusion will be on the sensor
8.2. larger aperture (smaller F-stop #) and closer focusing distances makes a shallow depth of field
9. other notes
9.1. need camera tripod or too small of an aperture softens the image by creating a larger circle of confusion due to an effect called diffraction
9.2. diffraction: becomes more of a limiting factor than depth of field as the aperture gets smaller.
9.3. macro photography(high magnification)= pupil magnification
9.3.1. equal to one for lenses which are internally symmetric.
9.3.2. not provied by lens manufacturers and can only roughly estimate visually