How would you like a better understanding of Bokeh
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Digital photography consists of many layers of technology. There is what
you need to know to operate a camera and compose great-looking
pictures, and then there is the science and highly technical concepts
that must work “behind the scenes” to give you the quality images you
expect. One of these concepts is bokeh.
This two-part http://moroccan-photography.blogspot.com/ article will explore bokeh because it
is important to understand and to recognize it in your photos and
through your lens
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For starters, bokeh is based on the Japanese word, “boke,” which
means fuzziness, or uncertainty. From that is derived bokeh’s
photographic definition, which is also a bit fuzzy. Bokeh refers to the
condition, or impression, of the areas of a photo that are not in focus.
It doesn’t measure the degree to which these areas are not in focus.
Instead, it is the nature, or the quality, of the blur created by these
areas that are not in focus. (You may want to pause and read this
paragraph again before proceeding because there will be more fuzzy ideas
to absorb.)
Bokeh and Your Lens
Every camera lens
is different in many ways: focal length, speed, etc. Another
characteristic of every lens is spherical aberration. When light waves
enter your lens, some are moving through the center of the many glass
elements in the lens. Other light waves are striking near the edges of
the elements. The glass elements have spherical surfaces, but they are
not perfect. Each has minute imperfections. The spherical nature of the
glass and the imperfections cause the light waves near the edge of the
glass to focus shorter than the light waves entering at the center. This
spherical aberration will create blurring in your photos. Spherical
aberration is not constant; so any differences will affect how your lens
depicts a point of light not in focus, or the point’s bokeh.
Now, imagine the light waves entering your lens after they have passed through all the glass elements, or are behind the lens.
If your lens were perfect, then it would gather all the points of light
into cones. If the single point at the end of the cone coincides with
the surface of the sensor, then the part of the image represented by the
cone of light is considered in focus. If the single point is in front
of the sensor or “behind” it, then that part of your image is not in
focus. Instead of a point registering on the sensor, a cross-section of
the cone, or a circle, represents the light. This circle is often known
as the "blur circle," or "circle of confusion." (How appropriate!)
If you’re lens were perfect (with no spherical aberration), then this
blur circle would appear as evenly illuminated and with a well-defined
border. You don’t want this border because the optimum bokeh would
display each point as a blur, with no distinct edges. If the circles had
sharp perimeters, then the parts of your picture that you don’t want in focus (to blur on purpose) would start to become unintentionally clear.
As mentioned above, all lenses have spherical aberration and are,
therefore, not perfect, so it causes the circles to appear with
inconsistent illumination. Typically, more of the light can be seen in
the middle of the circle or near the edges.
The Bokeh Spectrum
Although bokeh cannot be measured, it can be described according to a spectrum of its quality or character.
Inferior bokeh: This is the sharp-edged circle with a muted center.
Perfect bokeh: From a purely scientific point of
view, this bokeh is perfect because the circle is equally illuminated
and the border is distinct. Of course, you don’t want perfect bokeh.
Correct bokeh: The border of the circle is hazy,
which is caused by spherical aberration. The imperfections of the lens
surface actually create the best bokeh and better digital photos.