[5-18] "lux versus f-stops"

Photographers measure light with stops.

"1 stop, 2 stops, 3 stops."

Stops refer to light intensity reaching the camera (powers of 2).

"I need 1 more stop" => double the light (2^1)

"It got 4 stops darker" => 16x less light (2^4)

Every photographer gets used to it.

To compensate for darker scenes, photographers can adjust:

· shutter speed (slower)

· aperture (larger hole, lets in more light)

· ISO (a characteristic of a film, or an electronic change in how light is read by a digital camera)

EV (exposure value) describes more the absolute intensity of light of the scene.

EV14 -> sunny daylight

EV4 -> candles

I recently adopted a "lux" (see picture) meter. It analogously measures light but non-logarithmically.

Lux indicates how much light falls on a surface.

I pace the lux meter at my wall, I know the summation of light that hits it. Simple!

The technical stuff gets complicated very quickly (candelas, foot-candles, etc.).

Our eyes are constantly adjusting to light intensity. It's testament to visual adaptation that we can read in dim environments (~10 lux) as well as play sports in bright ones (40k+ lux), meaning our eyes can see and discern objects with over a 4000x change (~12 stops) in light intensity. Such is why cameras and film devices fail to capture as comprehensive a range as our eyes do; walking under bridges, we see shadows and highlights simultaneously, but the camera often cannot; photographers must choose.