This is important! It is inseparable from the discussion of DOF.
What is in focus and what is out of focus:
For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal pointsâ??one on each side. The distance in air from the lens or mirror\'s principal plane to the focus is called the focal length.
Put simply, the focus ring on a camera moves the lens within the camera, changing its focal length (I am a little fuzzy on this because if focusing does reposition the lens, it should then change the focal length. This would then affect the http://rtf318.pbwiki.com/Quantity%20of%20light. To my knowledge, adjusting the focus will not affect your http://rtf318.pbwiki.com/Quantity%20of%20light). This, in turn, causes the image within the viewfinder to become more or less blurred. Edit: Focusing does not affect the focal length. Focusing moves different elements in the lens than the zoom does. Out-of-focus images will have the same exposure as focused ones, though the blur may blend some of the lighter and darker regions.
- Technique:
- 1) Turn a ring on barrel of lens
- 2) Zoom in, set focus, zoom out
- 3) Tape measure: measure camera to subject distance, set ring accordingly
Selective focus will be covered separately.
