Extremely shallow portrait. Only Kuiper's nose is in focus.

Depth of Field (Part 2)

Kuiper goes deep (into the field)

In part 1 of how selective focus & depth of field work, we learned that cameras have a sensor, a lens to focus light onto that sensor, and that our area of focus is actually flat, like a piece of paper held at arm’s length.

If focus is a flat plane, why do most pictures appear to have more than that in focus? ? That’s due to an effect called the CIRCLE of CONFUSION. Remember that focusing works by condensing light reflected off part of our scene down to a single point on our sensor. That’s what it means to have something “perfectly in focus.” ? However, that isn’t the only light entering the camera.

We also get light from behind and in front of where we’re focusing. That light misses the mark and is condensed either behind or in front of the sensor. ? If it only misses by a little bit, that ends up looking like an teeny tiny circle on our sensor instead of a point. Make sense so far?

That “CIRCLE of CONFUSION” on our sensor is bigger than the perfectly focused point. However, as long as it’s not too much bigger, it’s going to appear as if that part of the picture is in focus too. It’s “good enough” as far as our eyes are concerned. Exactly how big that circle can be and still appear “in focus” depends on a few factors, including how big you enlarge the image, viewing distance and how good your vision is. Regardless, the further away from the subject, the bigger the circles of light. Once they exceed the COC size, we consider that part of the picture “out of focus.”

The photographer has a lot of control over depth of field through a setting called aperture (adjusting the “hole” in the lens to be either bigger or smaller). With a big hole (“wide” aperture) we let in more light, which means the circles enlarge quickly. The “too big to appear in focus” threshold is quickly surpassed, so less overall appears in focus. With a small hole (“narrow” aperture), we let in less light, so the circles are smaller. With a narrow aperture, we can look further from our subject before the picture appears out of focus.

Questions? What else would you like to learn about? Focal length? Bokeh? What makes a pixel a pixel?

Original post: https://www.instagram.com/p/Bqi9sxXDJj1/

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