Manual exposure variations - why?

Started Jun 4, 2012 | Discussions thread
Victor Engel
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Re: Manual exposure variations - why?
In reply to Andre Affleck, Jun 7, 2012

I think there are two main things that normally show up. The first has to do with the shape of the blades and controls the shape of the blur outline and radiating diffraction lines, like the star shapes you get around specular reflections.

The second is easiest to explain this way.

Imagine a blur spot that typically has a center and a roughly circular area around the circle. Imagine a line going from the center to the perimeter of the blur disk. Chart the brightness of the blur disk as you travel down this line. The she of this curve is a measure of the Bokeh.

There other things, like the blur circle being distorted away from the center, but I think those are the two most significant ones.

Andre Affleck wrote:

I always thought that bokeh encompassed all aspects of the out of focus areas, including the blurred circles. What visual effect do you see with bokeh then?

Victor Engel wrote:

Bokeh would only change to reflect the inconsistency between outside and inside of the lens. If the lens design is very uniform, the Bokeh would remain about the same, but the size of the blur circle would change.

Consider, for example, the theoretical perfect lens that produces Bokeh that renders a distant specular light as an even, filled circle. Changing the aperture of this perfect lens results in a perfect, filled circle of a different size. The Bokeh is the same. It's just the size of the blur that is different.

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