Why does a smaller aperture size have a high depth of field? What is the physics behind this?

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    @PhilipKendall This isn't a duplicate. The linked answer states the aperture results in DoF but this person already knows it, and is asking about the physics behind it. – Hairy Dresden Mar 16 '18 at 15:30
  • @HairyDresden - a) the OP has the premise in reverse & b) did you look at the 2nd answer on the dupe? – Tetsujin Mar 16 '18 at 15:41
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    We do have the technical question too. – mattdm Mar 16 '18 at 16:05

Why does a smaller aperture size have a low depth of field?

It doesn't; you've got it backward. Decreasing aperture size increases depth of field.

What might be confusing you is that smaller f-numbers indicate larger apertures. For example, an aperture setting of f/2 indicates a larger aperture than does f/2.8.

  • I edited the question. Sorry my bad! – physics2000 Mar 16 '18 at 16:12

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