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Auto Focus Question

Discussion in 'photo' started by garyi, Feb 9, 2006.

  1. garyi

    garyi leave blank

    How does a camera know its in focus?
  2. Joe P

    Joe P certified Buffologist / mod

  3. snowflake

    snowflake Former Albino Ape

    Magic moon beams fire from the camera and bounce back off the object, by doing some hard sums the camera can calculate that time taken = this distance and focus..........

  4. garyi

    garyi leave blank

    Joe I like the sense of community and you are beginning to sound like a twonky photonet forum user ;)

    The rather excellent news is my iMac has been dispatched today. Yippee.
  5. Joe P

    Joe P certified Buffologist / mod


    I don't mind answering questions or offering advice on lenses and cameras, but you have this annoying habit of not even reading the reply when someone goes to the trouble of answering your question. That's really more the hallmark of twonky photonet forum user.

  6. zener

    zener fluff

    the auto focus system has to be calibrated , it would be quite easy to make an auto focus system that doesnt , by not doing the calibration / set up properly at the factory.
  7. michaelab

    michaelab desafinado

    As well as image analysis for contrast (as mentioned in the pdf linked by Joe) many (most?) cameras also use an infrared beam and sensor to measure the distance to the subject. Good AF systems use a combination of the two. In your old E-10 Gary, it used image analysis preferentially but in very low light conditions where there's not a good enough image to work with it used IR sensing hence allowing autofocus to work even in pitch black conditions.

  8. garyi

    garyi leave blank

    I am noticing that the ability of the AF seems very lens specific. The older AF lens I have here suffers in lower light compared to the stock lens. My new super zooms focuses very quickly.
  9. ErikL

    ErikL pfm Member


    I missed the story behind this. Unless it wasn't told here. Did your other Apple(s) break and need to be replaced?
  10. garyi

    garyi leave blank

    No Erik, I am a sad apple fan boy, sold my 23inch and powermac and got an intel iMac
  11. Paul L

    Paul L coffee lounge for me

    Left field answer: It doesn't, the photographer does when he used pre-focus, zone focus, hyperfocal technique etc., used the lens markings (lenses from the olden days...) etc.

    I suspect Vuk will be along soon and add that a camera is never in focus, it really is up to the photographer to decide what he wanted sharp and use the attributes of the composition and the lens characteristics as he requires.

    Alternatively, it's something to do with CCDs, cross-hair sensors and maths calculations as previously suggested, used to be a big thing in camera brochures, don't know if it still is.
  12. Joe P

    Joe P certified Buffologist / mod


    Here's a review of the new iMac, while you're waiting for yours to arrive.


  13. garyi

    garyi leave blank

    The issue with rosetta is interesting. More interesting is who exactly thisd shit app is aimed at. How many people are likely to sit across a sitting room and squint at a 20 inch iMac haha.

    Its been resovled thankfully, a software issue.
  14. garyi

    garyi leave blank

    Booo, TNT have just left work without my Mac on board, no mac wankery this weekend then.
  15. matthewr

    matthewr spɹɐʍʞɔɐq spɹoɔǝɹ ɹnoʎ sʎɐld

    "How many people are likely to sit across a sitting room and squint at a 20 inch iMac haha."

    The so called "10 ft interface" and the personal computer as media centre is actually meant to be the latest great strategic growth area that powers Apple from 3% market share to world domination.

    I don't buy it either.
  16. garyi

    garyi leave blank

    The fundemental fuck up as far as I can see is that you cannot to date run front row on another screen, it has potential if you could do that.
  17. michaelab

    michaelab desafinado

    I can't see anyone taking Front Row or Microsoft Media Centre seriously at the moment. They're just gimmicks IMO.


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