Something I've noticed about the 3GS autofocus / touchfocus

Discussion in 'iPhone' started by danpass, Jul 13, 2009.

  1. danpass macrumors 68020

    danpass

    Joined:
    Jun 27, 2009
    Location:
    Miami, FL
    #1
    As we know the 3GS camera picks a spot and focuses on it. We also know that touching a spot on the screen overrides the camera choice and in addition adjusts the exposure accordingly.


    I was taking some outdoor shots today and it seems that, even if the two focus spots are the same, that camera autofocus and touchfocus on the same spot will yield different exposure results.

    Touchfocus will essentially establish a spot meter in conjunction with the smaller focus area.


    I'm going to continue testing further to confirm.
     
  2. Merkie macrumors 68020

    Joined:
    Oct 23, 2008
    #2
    No need to confirm this, this is a known feature of the 3GS camera.
     
  3. BittenApple macrumors 6502a

    BittenApple

    Joined:
    Nov 29, 2008
    #3
    From Apple's website.
     
  4. blulegend macrumors regular

    Joined:
    Apr 15, 2008
    #4
    I've had poor success with getting the iPhone 3GS to spot meter. It seems to always revert back to its own full-scene metering. I find that most of the time, my subject is grossly underexposed by the iPhone and I can't get it to spot meter.
     
  5. kas23 macrumors 603

    kas23

    Joined:
    Oct 28, 2007
    #5
    He's not talking about the fact that it focuses on one spot, but about it spot metering only the small area you tap, not the whole frame. That is, if you tap-focus on a very bright small area and snap a pic, the whole shot is going to be grossly overexposed.
     
  6. panoz7 macrumors 6502a

    panoz7

    Joined:
    Nov 21, 2005
    Location:
    Raleigh, NC
    #6
    I think you mean underexposed.
     
  7. CalMin macrumors 6502a

    CalMin

    Joined:
    Nov 8, 2007
    #7
    Depends on the conditions and subject.
     
  8. panoz7 macrumors 6502a

    panoz7

    Joined:
    Nov 21, 2005
    Location:
    Raleigh, NC
    #8
    I was commenting on this quote by kas23:

    If there's a small part of a photograph that's very bright and you tap on it, the iphone, at least according to this thread, reverts to spot metering and attempts to properly expose that very bright section at the expense of the rest of the image. Kas23's hypothetical area is much brighter then the rest of the image so in order to make it a reasonable brightness the camera's going to have to underexpose the rest of the picture. Kas23 had the right idea... I think he/she just said it backwards.

    I can't think of a single situation where spot metering on a small bright section of the photo would result in a grossly overexposed picture.
     

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