[5-28] "Aperture-priority"

What's the "best" aperture for portraits?

Many say, the simple answer is the biggest aperture.

The biggest aperture produces the most bokeh; bokeh is all vogue today.

Larger apertures are more expensive than the same lens offering a smaller aperture. Nikon makes a few prime (fixed) lenses with a smaller and larger aperture (35/50/85mm); naturally, there is competition and ego when photographers compare the size of their lenses.

Closer look, the 85mm (fixed) at f1.8 v. 1.4:

Depth-of-field : 6.2 v 4.8cm (in front of subject)
Background blur : 1.377 v 1.770mm (describes the relative expansion of blur of a background object at infinity) (via DOF simulator)

Strict interpretation:

• DOF = describes the "depth" of image, at a measured distance from the camera, containing sharp (not blurry) detail
• Less depth ("shallow DOF") = more bokeh (e.g. "shallow" referring to less depth, like water);
• Easy to think of DOF (for a portrait) as starting at the eyelash (in focus); more DOF includes the base of the nose, the sides of the face, the tip of the nose, hair, shoulders (should they be farther than the eyes).
• Background blur refers to the intensity (size) of blur of far away objects (also bokeh).

This is very interesting because for years, I did not know there was difference between DOF and BB.

This distinction proves useful in seeking bokeh and understanding certain "physical" or optical characteristics of lenses (not brand characteristics).