ISO Question

Discussion in 'Photography Beginners' Forum' started by lovinglifeinc, Jun 20, 2006.

  1. lovinglifeinc

    lovinglifeinc TPF Noob!

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    This may sound silly....but, I am trying to understand the terimnology of photography.

    What does ISO 800 mean to ISO 400? What is the difference...and what doe ISO have to do with camrea's or photography?:er:
     
  2. Wigwam Jones

    Wigwam Jones TPF Noob!

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    ISO has to do with how sensitive the film is to light. Each doubling of the film 'speed' (another way of saying ISO) is twice as sensitive to light.

    Thus, ISO 200 is twice as sensitive as ISO 100.
    ISO 400 is twice as sensitive as ISO 200.
    ISO 800 is twice as sensitive as ISO 400.

    And so on. Faster film (higher ISO) means you can shoot with a faster shutter speed in darker conditions - meaning less chance of blurring your subjects through camera shake. However, there is a trade-off (there is always a catch). Faster film tends to be more grainy and less realistic.

    So it is a good idea to use the right speed film for your conditions. ISO 100, 200 are good for bright sunny days outdoors. ISO 400 is a good all-purpose in and outdoor film. ISO 800 is for indoors when you can't use flash readily.

    Hope you find this helpful.
     
  3. Arch

    Arch Damn You! Staff Member Supporting Member

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    The ISO level is basically how sensitive you want your camera sensor to be to light....... so ISO 100 would be less sensitive and could be used for a daytime or well lit shot to produce sharp well balenced images....... where as ISO 800 would increase the sensitivity and be able to produce better results in low light situations........ the only downside is, increasing ISO can add noise to the image. ;)

    EDIT: wigwam beat me to it........... and its a better discription than mine ;)
     
  4. Aelfwyn

    Aelfwyn TPF Noob!

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    So what's the difference between changing the ISO and changing the shutter speed?
     
  5. Luke

    Luke TPF Noob!

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    right, looks like yu should google this.
    to be correctly exposed an image has to let the right amount of light in. thus if its really dark, and you set your shutter speed really fast, not much light is gunna get in and your image will be to dark. higher iso, means that the camera is really sensitive to light, so it needs less, and you CAN shoot at higher shutters.
    google exposure, or pick up a book.
     
  6. ThomThomsk

    ThomThomsk TPF Noob!

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    You control your exposure with aperture and shutter speed. Changing ISO gives you a different range of possible aperture/speed combinations for the correct exposure for a particular scene.

    For example, shooting handheld in artificial light (say a concert or a school play) I might pick a 3200 ISO film because it allows me to use a decent shutter speed in spite of the low light level, but I'd pay the price with relatively grainy images (although that might be what I wanted). Shooting landscapes from a tripod I'd choose a 100 ISO or even 50 ISO film, because I want to set my aperture at f22 for maximum depth of field and I don't care if I have 1 or 2 second exposures, but I do want the lowest possible grain.
     
  7. Aelfwyn

    Aelfwyn TPF Noob!

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    Ah, OK. Think I understand. Cheers, guys!
     
  8. Philip Weir

    Philip Weir TPF Noob!

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    I always use the "bucket of water"example when teaching novices about about ISO, aperture and shutter speed. You have a pipe pouring water into a bucket. The pipe size is the aperture, the speed of the water is the shutter speed and the pressure is the ISO. A full bucket is the correct exposure. A large pipe [large aperture] would fill the bucket in a very short time [short exposure]. A narrow pipe [small aperture] would take longer [long exposure]. Doubling the water pressure [ISO] would half the time for either operation. Trust this makes sense. It's easier to explain than write, trust you get it. Philip.

    www.philipweirphotography.com
     
  9. Aelfwyn

    Aelfwyn TPF Noob!

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    Oh, thanks, Philip, that does make sense! Excellent explanation, thanks! :D
     
  10. Unimaxium

    Unimaxium TPF Noob!

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    Here are a couple links that give a very thorough explanation of ISO (a.k.a. ASA), shutter speeds, and f/stops. The first link mainly deals with shutter speeds and f/stops, and the second link ties it in with ISO ratings as well. Although Philip's explanation sums it up pretty nicely as well.

    http://www.uscoles.com/technical.html
    http://www.uscoles.com/fstop.htm

    Also, there's a thread that used to be stickied at the top of this forum that had a bunch of explanations for beginners, but it seems to have gone missing and a quick forum search didn't turn it up. Perhaps if a mod could try to find it and stick it back up? I thought it to be quite useful.
     

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