Infinity

Discussion in 'Photography Beginners' Forum' started by julie32, Jan 19, 2008.

  1. julie32

    julie32 TPF Noob!

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    Can someone please briefly explain the concept of infinity to me? Of course, as it relates to photography! (otherwise we'd be here all day....though I may be here all day anyway.)

    thanks,
    J
     
  2. RKW3

    RKW3 TPF Noob!

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    "Infinity focusing locks the focus at the far end of the standard autofocus range so that objects at a distance appear in sharp focus. Sometimes labeled with an infinity symbol, this setting is great for landscape photos.
    Because the focusing ranges for each mode vary from camera to camera, check your digital camera's manual to find out what mode is appropriate given the distance between you and your subject."


    that's from this link I found in a google search: http://tech.yahoo.com/gd/working-with-your-digital-camera-s-autofocus-mode/153054
     
  3. julie32

    julie32 TPF Noob!

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    Thanks Robbie....

    Are you able to explain it in layman's terms? Like.. what's the purpose of it, why can't we "focus on infinity" in AF mode? or how it relates to everything else in the photo etc...

    thanks
     
  4. fatsheep

    fatsheep TPF Noob!

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    I'd like to hear a good explanation on this as well. *subscribes*
     
  5. Ls3D

    Ls3D TPF Noob!

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    Well since no pros have chimed in, yet - here is my stab:

    Because your focusing engine will find objects closer that the furthest point and is designed for sub infinite focus. Besides it is just so natural to manual focus the distant objects in your FOV. Or sometimes just set it for X number of feet from where your shooting. I'm still experimenting with this myself.

    Being a layman, perhaps. Infinite focus is for times when you just want to capture the whole scene as is with everything, (or nearly everything in focus). A field of flowers that also has an interesting landscape and mountains in the distance for example. Conversely DOF shots are more creative in nature as you have explicitly sought out to soften backgrounds or to isolate an subject.

    Loosing me now, but be aware large apertures (small f/stops) will allow too much light in (scatters) and therefore blur objects outside the focal point. Small apertures (large f/stops) will limit the amount of light and are key to creating images with near infinite focus.

    Now that I've spoken up I'm sure some more people will have something to say, so I stand corrected in advanced.

    -Shea :mrgreen:
     
  6. Josh66

    Josh66 Been spending a lot of time on here!

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    I'm not a pro either, but...

    I think this is a situation where you would want to focus to the hyperfocal distance of your lens. Google "hyperfocal distance" if that term is unfamiliar to you.
     
  7. yeti

    yeti TPF Noob!

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    Here is my two cents:

    juli32, I want you to look out your window on an object fairly close. You have two eyes (I assume) and as your eyes focus on an object, they no longer look straight ahead, but rather slightly cross-eyed.

    Looking at an object further away, your eyes get less cross-eyed to give you depth perception again.

    Looking at things even further away, your eyes start making smaller and smaller adjustments until you finally set your two eyes to watch straight ahead. Your eyes stop being cross-eyed entirely. Your brain cannot make so fine adjustments to your eye location and it doesn't need to: something so far away is unlikely to be a danger to you. To be exact, you don't have depth-perception for objects more than 40m away. No human does.

    Well your camera doesn't get cross-eyed but it has a much larger front element. As you focus, you select light coming from certain angle to be in focus. As you focus to infinity, you receive light coming from very distant objects. Your lens receives them all at angles so similar that your lens can't tell the difference. This means that they are all in focus, regardless of their distance from you. This is focusing at "infinity".

    I tried to explain it in layman's terms. But at the end of the day this is nothing more than the concept of limit, and as far as focal distances go, the limit is finite.
     
  8. Saint-Brown

    Saint-Brown TPF Noob!

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    Even though I know what it is, it is alway good to hear it explained
     
  9. Alex_B

    Alex_B No longer a newbie, moving up!

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    if you focus on the moon, then this in first approximation is focus to infinity. This also works with AF.

    Just most objects are not infinitely away, not even approximately! They are closer.

    Infinity means in a simplified explanation, that light which comes from an object at infinite distance is parallel. hence to focus, the lens has to converge this parallel light in one spot on the film/sensor.

    i think some illustrations might help here ;)
     
  10. julie32

    julie32 TPF Noob!

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    thank you for these helpful explanations! YETI--- I laughed so hard when you said "you have 2 eyes, (I assume) ......"
    I did exactly what you told me to do ...and I totally understand what you're saying, so thank you very much!!
     
  11. fatsheep

    fatsheep TPF Noob!

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    That makes sense. However, is "infinity" (in photography terms) a certain distance away? Or does it depend on the lens? Is there a way to find out how far away infinity is for a given lens?
     
  12. chris

    chris TPF Noob!

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    Infinity is a number greater than any assignable quantity, simply, it is an unimaginably large number.

    Light from an object an infinite distance away would arrive at a positive lens as parallel rays and would be focussed behind the lens at a distance equal to the focal length measured from the rear nodal point of the lens. Objects nearer to the lens would be focussed farther behind the lens.
     

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