[5-19] “Bokeh in Broad Daylight”

A typical natural light wedding or portrait photographer will use a long lens (>50mm), large aperture (>f/2.8).

This results in bokeh, or out-of-focus (behind subject).

DOF decreases as:

•  larger aperture

•  longer lens

•  larger sensor

I think of aperture as a “web”. A lightbulb fires [rays of] light. A room brightens: walls, ceiling, floor. Rays of light are straight lines “hitting” painted surfaces, bouncing; walls are visible to your eye.

Now the aperture is like the wall: it’s just a surface. This piece of glass is like a magnifying glass; it changes light direction so these rays of light converge at a single point.

That’s gist of optics. Rays of light exiting a light-emitting source “recenter” (i.e. focus) at a tiny point on a sensor.

If you want bokeh (big aperture) in broad daylight, overexposure is a problem. Reduce shutter speed:

1/1000 (good) -> 1/2000 (better) -> 1/4000 (the fastest shutter speed)

Light sensitivity (ISO) should be very low:

400 (ok) -> 200 (better) -> 100 (lowest)

At f/1.4, proper exposures is EV13

Not good if it’s brighter (>13 EV).

At EV 15, we have 4x more light than EV13.

Camera manufacturers saw this and offer options in higher-end cameras:

1/4000 -> 1/8000 (cuts half exposure)

ISO100 -> 64 (66% less light sensitive)

This is 1.67 stops, so now we can safely shoot at an EV of 14.677.

For anything brighter, an ND filter is required (this cuts light, doesn't change color/UV/polarized light).