Aperture in Photography

(Or how Bokeh happens?)

Guilherme Zühlke O’Connor

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BOKEH? WTF?

When light hits an unpolished surface it spreads rays of light in all

directions

A Photo Camera is a device to single out an organised cone of

rays of light.

Ideally, an infinitesimally small hole would let in a single ray from each

point of the subject

In Practice the hole has dimensions and therefore multiple rays from

each point are projected.

Mutiple Rays from a single point

• Create multiple slightly displaced images of the same object

Mutiple Rays from a single point

• Create multiple slightly displaced images of the same object

• More rays of light coming in means more light

Mutiple Rays from a single point

• Create multiple slightly displaced images of the same object

• More rays of light coming in means more light

• Film (or sensors) depend on light to create images. The more light, the merrier.

But multiple images slightly displaced means you can’t single

any one out.

But multiple images slightly displaced means you can’t single

any one out.

That’s blur for ya!

…so cameras have lenses to make these multiple rays of light

converge into a single image

More Light, and no blur!

But wait!

What’s the bokeh again?

In photography, bokeh is the blur or the aesthetic quality of the blur, in out-of-focus areas of an image, or "the way the lens renders out-of-focus points of light."

http://en.wikipedia.org/wiki/Bokeh

http://www.flickr.com/photos/ashumittal/4940709917

Well, it turns out that the lens can only make converge rays of light coming from given distance from the lens at a time.

Well, it turns out that the lens can only make converge rays of light coming from given distance from the lens at a time.

This means if you adjust the lens to focus at one point. Objects will be progressively more blurred the further or nearer they are.

The wider the aperture, the more blurred your bokeh will be.

But also the more light reaches the sensor or film, which means faster shots and higher definition.

Let’s do the Math, shall we?

f-stops, the measurement of aperture.

f = Lens Focal Length / diameter of aperture

f-stops, the measurement of aperture.

f = Lens Focal Length / diameter of aperture

Focal length = 50mmDiameter = 12.5mm

f = 50 / 12.5= f/4

The incoming light is proportional to the area of the aperture.

Area = πr2

Focal length = 50mmDiameter = 35.7mmf = 50 / 35.7 = f/1.4

Focal length = 50mmDiameter = 12.5mm

f = 50 / 12.5 = f/4

Focal length = 50mmDiameter = 17.6mmf = 50 / 17.6 = f/2.8

Diameter X 1.4Area X 2Light X 2

Diameter X 2Area X 4

Light X 4 (*)

(*) And lots of bokeh!

Further reading:http://www.z-oc.com/blog/2007/08/understanding-cameras-and-photography/

?Questions?