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I was wondering how auto-focus works in mobile cameras. I understood that, mobile phones uses either 'contrast based' or 'phase-detection based' algorithms to find the optimum length position for maximum sharpness of the image frame.

So, In my iPhone 12, I conducted one experiment.

  • I shot an image of subject which is close enough. So, auto-focus worked, only subject was sharp, and background was blurred.
  • I shot another image in which is subject was far. I tapped on the subject for focus. And subject was sharp and near by objects were blurred.

Then I checked the metadata, and found that, both the cases focal length was 26mm only. Only there was small difference in ISO and shutter speed (may be due to light intensity)

My question is, How iPhone (any phone for that matter) is able to auto-focus without changing the focal length?

I know that, even aperture can be used to get the focus (depth of field), but I believe, aperture is fixed in iPhone (and most of the mobile phones).

edit: This question didn't completely answer my question. I am mainly looking for how camera (specially smartphones) focuses without changing focal length (and have fixed aperture)

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  • \$\begingroup\$ @Aravind welcome to Photo.SE! It appears that the question you're asking has been answered before. If that's not the case, feel free to edit your question and indicate what aspects are not answered by the presumably duplicate question. \$\endgroup\$
    – Saaru Lindestøkke
    Commented Jun 21, 2023 at 16:13
  • \$\begingroup\$ Thanks! Edited question by providing more details \$\endgroup\$
    – Aravind D. Chakravarti
    Commented Jun 28, 2023 at 7:20
  • \$\begingroup\$ There's nothing fundamentally different between how a smartphone does this and how any other lens does this; to quote from the accepted answer "A prime lens still has a moving focus element allowing you to change the focal plane". The applies as much to my 50mm f/1.8 lens as it does to whatever lens is in a smartphone. \$\endgroup\$
    – Philip Kendall ♦
    Commented Jun 28, 2023 at 7:37
  • \$\begingroup\$ Oh okay. So, should we consider smartphone camera's as prime lens only? \$\endgroup\$
    – Aravind D. Chakravarti
    Commented Jun 28, 2023 at 8:36
  • \$\begingroup\$ "Prime" means just "cannot change focal length" so, yes. \$\endgroup\$
    – Philip Kendall ♦
    Commented Jun 28, 2023 at 9:52

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