Sunday, June 19, 2011

Bokeh - Playing With Light

I spent some time fooling around with my sister, studying the effect of Bokeh. Bokeh is essentially the intended effect of blur in a photo, or the lack of focus. By controlling what is or isn't in focus in a photo, you can create a specific look or aesthetic quality that is unique and eye catching. A great example of this is in the Kelly & Chad Wedding, in the picture of the gift box. By using a wide aperture (f 1.8), and close up shot, you can create a 'shallow depth of field' and draw focus onto one of the gift boxes while the rest are out of focus. My Uncle was interested in the effect seen in that photo, so I thought I would use it as a topic...This one is for you E!

How does it work? There are 2 basic ways of controlling the depth of field - The f-stop and the magnification. The smaller the aperture or f-stop, the wider the opening, and therefore, the shallower the depth of field. Magnification can be achieved through your lens, or by physically moving closer to the subject. The more magnification, the shallower the depth of field. This will cause whatever you focus on to be in focus, and the background or foreground to be blurry and out of focus from abberation of light. What the heck is that? The idea of capturing light is to have each point of light captured on the cameras sensor at the exact point where the cone of light reaches its smallest point...perfect focus. The better the lens, the smaller this point will be...better resolution. But if the light is projecting from an out of focus point, the light will not reach the sensor at its finest conical point, but rather diffuse outward and collect in a circular shape. A camera lens automatically renders out of focus light as discs of light or circular shaped light due to the shape of the secert here its a circle. Ideal bokeh with have undefined, soft diffuse edges...but the reality of bokeh is usually sharp defined edges depending on the type of lens used. Lenses with better spherical abberation will cause the light to appear more spherical, with a stronger light focus in the centre and a nice 'fading' or diffusing of the light toward the edges (as opposed to evenly lit discs of light). This is achieved by having more blades, which form the aperture opening, the more blades the smoother the circle (i.e 9 as opposed to 7 etc.). Of course, it depends on the effect you are going a portrait for example, diffuse, and undefined bokeh would make a more aesthetically pleasing photo. In the case of light the examples here, the more defined and evenly lit shapes create the desired effect.

Defined edges versus undefined edges 

In the following photos this effect was applied, but was enhanced by using a lens filter. I constructed a lens cover out of black construction paper, which I hole punched a heart shape out of in the centre, about 1cm across. Instructions on how I made it can be found here:

Keep reading below for an explanation of how it works!

This has no filter on it at all....the bokeh is circular because your lens is circular

Why does this effect work, and why doesn't the entire photo appear to be in the shape of a heart? First of all, you must have a lens with enough magnification or else you will end up with a dark heart shape around your photo (50mm works nicely). The answer is complex, but can be simplified if you think of your camera like a human eye. As light passes through your eye via the cornea, pupil and finally the lens, it is refracted and inverted, then interpreted as the image is translated to the brain. Your pupil acts the same as the aperture in your camera by dilating or widening to allow more light in, or restricting to allow less light in. It will also widen when focussing on something close up, creating a shallow depth of field in the same way as discussed above! Try it out, hold your finger close to your eyes and get someone to watch your pupil dilate, now use your peripherals and see how everything behind your finger is blurry! You’ve achieved natural bokeh! Biology is awesome isn’t it? Now, back to comparing your eye to your camera… The lens in your eye bends and refracts light much in the same way as the lens in your camera; however our eyes do not have a zoom function (!) so think of your eyes as a prime lens. Finally your retina absorbs the refracted light, and translates the information to your brain where it is interpreted; this is equivalent to the sensor in your camera in this comparison which also processes the information to create a digital image.

To summarize: The lens in your eye bends and refracts light, just as the lens of your camera does. The light is 'captured' by the retina, similar to the sensor of your camera, and then converted by the brain into a visual image you can interpret, or for a photo, a digital image on your display screen. Because a camera, like your eye, can only see images and objects if there is light reflecting off of them, there must be some light allowed to enter, but we can control the shape as described above.

With this restriction of light allowed to enter the lens, regular and in focus objects will appear as normal, but out of focus, direct sources of light will be heart shaped, as we have changed the shape of the aperature essentially. Regular objects will still reflect light in all directions and angles, as the image is visualized by bouncing direct light around. The light rays being bounced back at your camera lens will pass through the heart shaped cut-out at many different angles and therefore appear as normal as it will access the entire sensor, and will be in focus. However, any source of direct light, such as a light bulb, a streetlight, or in the case of my photos a string of Christmas lights, which are out of focus due to the shallow depth of field, will be beamed directly at the heart shape cut-out in a straight path, and therefore will only enter the lens in the area where the shape allows, and be blocked by the black construction paper, thus creating a heart. This occurs as lenses render out of focus points of light as circles, due to the shape of the lens (as above), but by changing the shape which the light enters the lens, we can change the shape of the out of focus points.

Try it yourself…the image reflected to your cameras sensor is inverted, exactly like the light we see is inverted onto our retina; our brain processes the information so we see it in the correct orientation, as does your camera's sensor. If you move too close to a direct light source, the light path won't be long enough to enter and invert through the lens….what will happen?? It will fool the camera sensor and actually cause the heart shapes to be upside down! Don't believe me? Try it out!

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