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iPhone / Mobile Depth of Field Question

Discussion in 'Smartphone photography' started by MegaBeaker, Jul 25, 2016.

  1. MegaBeaker

    MegaBeaker New Member

    Hi All,

    Just got a simple question that I'm hoping someone knows the answer to. I've tried Google searching this but can't seem to find the right answer.

    Using the iPhone is the easiest example to use but really it applies to all camera phones. The lens on an iPhone 6s is f/2.2 so how come it doesn't have a very shallow depth of field? I'm guessing it's something to do with either the lens its self or sensor on the phone. I'd be interested to know the science behind it.

  2. EightBitTony

    EightBitTony Well-Known Member

    Depth of field is directly impacted by focal length, as well as aperture. For any given aperture, the depth of field will be deeper at shorter focal lengths than at longer focal lengths.

    Among other things, phone cameras have wide angle lenses, so naturally have deep depth of field.

    The sensors are also tiny, say, 1/3rd of an inch, and they give a 35mm equivalent focal length of around 30mm. But that's the 'equivalent' length, not the actual focal length / field of view. If you do the maths, it works out at something like a 6mm focal length on the iPhone. 6mm is crazy wide angle, and so has a very very deep DoF.
  3. RogerMac

    RogerMac Well-Known Member

    When I was in the sixth form at school we covered this in the physics syllabus but to do it properly requires a knowledge of differential calculus. Unfortunately that was 60 years ago and I no longer possess that knowledge. Fortunately it is very easy to demonstrate experimentally that short focal lengths have much greater DOF than longer focal lengths, and if you have access to a DSLR with a zoom lens it is possible to spend a happy 15 minutes setting up such an experiment.

    Whilst typing this Tony's post has appeared so I will not go on as he has answered the question.

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