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What about lens construction influences bokeh?

Does the circular or hexagonal shape of the bokeh depends on the number of elements and groups of the lens??

If not then how do the shape differs??

Edit: How to determine the characteristics of the aperture controls from the lens specifications?


In the bokeh, aou have two different aspect:

  1. the shape of the bokeh which is directly related to the shape of the opening of your lense. The shape is thus dependent of your f-number as this value will determine how the diafragma is closed when you shoot the picture, whide open the diafragma blades have a nearly round shape while when stop down they assume an octogonal shape (if your diafragma has 8 blades).

    • For out-of-focus lightsources near by the ligne of sight, the shape is marginally affected by the number of ellement and groups of your lenses.

    • However, excentred out-of-focus lightsources may have a truncated bokeh due to the fact that some of the light has encountered an obstacle (namely: the border of the lense) thus those truncated bokeh are dependent of the shape of your lense which is related to the elements and groups.

    • For prime lenses (when the optical center is close enough of the front lense), you can alter the bokeh shape by adding a chardboard cut with your prefered shape (just search 'custom bokeh' in google image to get sample and setup).

  2. The bokeh lighting, this is the way the light fill the bokeh, you may have an homogenous disk or a more bright ring on the border or a double ring or some dark ring and so on.

    • The lightning is deeply dependent on the optical formula and prime optic have usually much more eastetic bokeh than zoom lenses.

No, it doesn't depend on elements and groups of an lens. The aperture construction is responsible for the shape of the bokeh. For normal DSLR lenses the aperture diaphragm is constructed to create a round and pleasant bokeh. But there exist some specialised lenses where you can exchange the aperture diaphragm with a "design" of your own. Here on Flickr are some examples of different aperture shapes.

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