Iso and Shutter speed

Discussion in 'Photography Beginners' Forum' started by Mr.Bluesky, Jul 30, 2008.

  1. Mr.Bluesky

    Mr.Bluesky TPF Noob!

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    Does changing the iso have a direct effect on the shutter speed? What does iso do?
     
  2. bullitt453

    bullitt453 TPF Noob!

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    ISO controls how sensitive the digital media (or film) is to light. Therefore, yes, it does effect shutter speed. Using a higher ISO number, say 1600, allows you to use a much faster shutter speed in low light situations than an ISO of 100 would. However, higher ISO also means higher probability of noise in your image. I always try to keep the ISO as low as possible and simply use a tripod to allow for a longer shutter speed to capture enough light. However, this isn't always possible, like in places that prohibit tripods and flashes.
     
  3. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    There are three things (on the camera) that control/affect the exposure.

    The first is the aperture of the lens. The larger the aperture, the more light that can get it. Aperture is represented by F numbers...a lower F number is a larger aperture.
    The second thing is the shutter speed...the length of time the shutter is open. Obviously, a longer shutter speed (lower number) lets in more light.
    The third thing is ISO, which is the sensitivity as described above. On digital cameras, the ISO is raised by increasing the gain, or amplifying the signal from the sensor. The more you amplify the signal, the more distortion you get, which means more noise.

    So if the light remains constant and you want to keep the same exposure...changes made to one setting, can be offset by changes to another setting.

    For example, if your exposure is F8, 1/30 at ISO 100....you could get the same exposure with F8, 1/60 & ISO 200...or F8, 1/120 & ISO 400.
     
  4. Mr.Bluesky

    Mr.Bluesky TPF Noob!

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    thanks, now it makes more sense. Ive heard that the larger the aperture, the faster the sequence capability, is this true? it is important because I like taking skateboarding sequences.
     
  5. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Not really, no.

    Using a larger aperture will let in more light, allowing you to get a faster shutter speed to freeze the action...but it won't let you shoot multiple exposures any faster. That is a function of how fast your camera can shoot.
    The exception being if your shutter speed was slower than the camera's frame rate...which is probably 3 to 5 frames per second. In shutter speed terms, that would be really, really slow and your shots would be blurry anyway. To freeze action, you will probably want to be shooting at 1/125 or 1/250 of a second...which is much, much faster than the camera's frame rate.
     
  6. Mr.Bluesky

    Mr.Bluesky TPF Noob!

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    Thanks, I am shooting at about 2.7 per sec, my camera is only capable of three.
     
  7. Donald Harvey

    Donald Harvey TPF Noob!

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    Thank you that was helpful to me and I didnt even ask the question!
     

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