The much-talked about subject of "bokeh," refers to the visual character of the soft, out-of-focus elements in a given frame--the "shallower" the depth-of-field, the more exaggerated this effect becomes:
AF Nikkor 50mm f/1.4D @ f/1.4 (large aperture, close focus)
AF VR Nikkor 80-400mm f/4.5-5.6D ED; 400mm @ f/5.6 (narrow angle-of-view)
"Depth-of-field," is delineated by the nearest and furthest distances from the lens, between which, objects appear sharp at a given aperture--that is, objects within a certain distance range from the image plane, which appear "in focus." Technically, it's the area in which the "circles of confusion" (the focused points of light which make up your image) on the image plane are small enough, so that they look like "points," appearing "sharp" or "resolved," rather than "circles" (i.e. "bokeh"). When those points are small enough (e.g., 0.02mm), the portions of the image which they represent, appear "in focus." Small apertures (numerically, high, e.g., f/16), effect "deep focus," or wide areas of focus, where many objects in the frame are in apparent focus. Large apertures (numerically, low, e.g., f/1.4), effect "shallow focus," or narrower areas of focus, where fewer objects in the frame are in apparent focus, and produces the maximum degree of bokeh for a given lens. There are four factors which directly affect, or effect the appearance of, lesser, or greater depths-of-field:
1. Aperture: the wider the aperture (numerically, lower, e.g., f/1.4), the less depth-of-field. A small region of depth-of-field is termed "shallow," meaning, only a narrow plane (perhaps, only a few millimeters in depth on a fast lens), perpendicular to the optical axis, is in apparent focus.
2. Distance: the shorter the focused distance to your subject, the "shallower" your depth-of-field.
3. Angle-of-view: the narrower your angle of view (i.e., the more telephoto), the more that your depth-of-field will appear shallower (it's actually not any shallower, it's just that when using a telephoto lens, you're simply viewing your scene in a more magnified fashion, through a narrower field of view, so its effect is more obvious).
4. Size of image sensor: the larger the sensor, the shallower the apparent depth-of-field.
Employing shallow depth-of-field in any given shot, will magnify the visual effect of "bokeh." In other words, the more shallow the depth-of-field, the more the degree of softness in both your out-of-focus, foreground and background elements is increased. Bokeh is typically highly desirable to enable you to isolate your subject from distracting background elements by throwing those elements sufficiently out of focus, into a more "abstracted" blend of light, color, and diffused form. It's often used purely as an artistic effect.
The Nikon lenses often rated with the "best" bokeh are:
1. AF Nikkor 85mm f/1.4D
2. AF DC-Nikkor 105mm f/2.0D/AF DC-Nikkor 135 f/2.0D (Nikon's specialty, "defocus-control" lenses)
3. Nikkor 300mm f/2.8 (any version)
However, exaggerated bokeh effects can also easily be obtained with the more affordable, Nikkor 85mm f/1.8 (one of my favorite focal lengths), or the Nikkor 50mm f/1.4, Nikkor 50mm f/1.8 (though some feel that the bokeh from these 50mm lenses is too "hard"). While macro lenses also offer easily attained bokeh, macro lenses, such as the AF-S Micro-Nikkor 60mm f/2.8D, AF-S VR Micro-Nikkor 105mm f/2.8, are generally designed to be stopped-down to smaller apertures (higher, numerically, e.g., f/11), and are generally not as sharp as their non-macro counterparts, when shot wide-open at their maximum apertures (e.g., f/2.8).
AF Micro-Nikkor 60mm f/2.8D @ f/2.8
Edited by studio460 - 5/25/10 at 3:16am