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Phone camera extraordinary exposure details

Discussion in 'Talking Pictures' started by Rupert49, May 31, 2020.

  1. Rupert49

    Rupert49 Well-Known Member

    My sister recently sent me a photograph of her daughter (my niece) with her new baby son, born in lockdown. The picture is a general view of mother and daughter in the garden, surrounded by the usual trappings of being outside on a sunny afternoon. It's just a regular picture, reasonably well exposed and exhibiting full depth of field.

    Out of curiosity I had a look at the exif data and was amazed to see that the exposure parameters were as follows:

    Apple iPhone
    f/1.8
    1/1114 sec
    ISO-20
    Focal length 4mm

    As a long time user of SLR & DSLR cameras, those exposure details don't make any sense. How on earth could there be any depth of field at all? And yet the picture looks like a regular shot that I might have taken with my own camera using ISO-200, f/8.0, 1/250 sec.

    I have no acquaintance with phone cameras, so is this merely one of the quirks of their technology?
     
  2. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    The clue is in the focal length of the lens. With a focal length of 4mm the depth of field at f1.8 is going to cover a wide range. F1.8 on a bright day with an ISO of 20 means that a shutter speed of 1/1000 seems about right.
     
  3. spinno

    spinno Well-Known Member

    Artificial intelligence, and/or witchcraft
     
  4. PeteRob

    PeteRob Well-Known Member

    Depth of field increases as the focal length gets shorter. That's a large part of why digital compacts killed film compacts so quickly - suddenly everything is in focus - no more oof "failures". Plus the instant result means that an exposure error can be quickly corrected by taking another shot. Plus no D&P costs.

    ISO-20 looks a bit low - it might have a built in ND filter for bright days.
     
  5. Terrywoodenpic

    Terrywoodenpic Well-Known Member

    When it comes to phones cameras, witchcraft has it in spades.
    My Huawei Leica inspired cameras have a far better understanding of what they are doing than I or any of my Fuji cameras have. They seem to get it right every time.
    If you keep the maximum size to reasonable limits they are as good as any one might need.
     
  6. Stephen Rundle

    Stephen Rundle Well-Known Member


    4mm I would expect it to, but I don't see the photo to comment on
     
  7. RovingMike

    RovingMike Crucifixion's a doddle...

    Rupert, I don't know if you got what they are saying. Point that might not be clear enough is that 4mm is relative to the size of the sensor, which is of course tiny compared with your DSLRs. I've not done the maths, but it would certainly relate to your f8 on say a 28mm lens.
     
  8. PeteRob

    PeteRob Well-Known Member

    As I happen to have a calculator ... Depth of field relates to the actual size of the aperture, becoming greater and greater as a pin-hole is approached. The physical aperture on the phone lens (presumably wide-open) is 4/1.8 = 2.22 mm. On a 28 mm lens a physical aperture of 2.22 mm relates to an f number of 12.6. So over a stop down on f8.
     
    RovingMike likes this.
  9. Rupert49

    Rupert49 Well-Known Member

    Thanks Mike, that explains a lot! By the way, I forgot to mention that the precise Apple model was an iPhone 7 (if that's relevant at all).

    For Stephen Rundle's benefit, I tried to upload the photo from my Photobucket, but things there seem to have changed since the last time I used it, because all attempts to click onto the URL merely produce a box that says hosting is no longer available within my current plan .. except I haven't got a current plan, it's always been FREE! I now need to subscribe to one of their plans, but I'm such an infrequent user it hardly seems worth it. When did Photobucket stop being free? What's the situation with Flickr?
     
  10. PeteRob

    PeteRob Well-Known Member

    Photobucket blocked sharing of images on other sites a long time ago. There was much spluttering on here. Flickr still has a free option but for how much longer I don’t know. This forum now allows direct uploads (the upload a file option) but keep to forum guidelines (800 pixel max side) for best results. The file size is restricted but to something much bigger than the 300 kb or so an 800 pixel wide (or tall) file will be (uncompressed).
     
  11. Rupert49

    Rupert49 Well-Known Member

    Thanks for the general update Rob, I've obviously been away from here too long!

    I've just attempted the 'Upload a File' method to put the photograph in question on here, but the initial try produced an 'Amateur Photographer Error', i.e. I probably don't currently have the right permissions in place. Anyway, here goes again ..

    IMG_0391a.jpg
     

    Attached Files:

    RovingMike likes this.
  12. PeteRob

    PeteRob Well-Known Member

    That worked a treat.

    We have a grand-daughter, born in lockdown, and she seems to be getting the hang of zoom, not that she has any say in the matter of being plonked in front of a computer.
     
  13. Chester AP

    Chester AP Well-Known Member

    I had some confusion about lens apertures and depth of field when I moved from a 'full frame' 35 mm film camera to a 'half frame' APS-C DSLR. For me, the depth of field I expected at F 8 was now available at F 5.6 and the smallest aperture to use to avoid diffraction softening the image was now F 11 and not F 16. The minute sensor in the iPhone means that you have encountered a more extreme example of this, but the result is that it's virtually impossible to get a stationary subject out of focus if you can hold the iPhone still enough when you take the shot (I always notice users trying to do this with the device held at some distance in front of them).

    Comments above about the iPhone lens being 'equivalent' to a 28 mm lens on a full-frame camera look right - notice the diverging verticals in the fence panels and nearby house at the edge of the frame when the viewpoint is slightly above the subject.
     
  14. Rupert49

    Rupert49 Well-Known Member

    More than likely caused by the camera pointing slightly downwards, producing that divergent effect. We're more familiar with the opposite effect - converging verticals - when we point the camera up at a tall subject. The best way to avoid it is to take the picture from a mid-point position (vertical axis) or to use a tilt-shift lens. Since I'm not an architectural photographer, I'll pass on the latter and continue to resort to PS for correcting my verticals!
     

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