Difference between ISO and EV

Discussion in 'Photography' started by Danny1911, Jul 7, 2008.

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  1. Danny1911

    Danny1911 New Member

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    I have recently acquired a new digital camera from my father (a stylus verve). Anyway I decided to learn all of the terms in the menu and different techniques behind the picture, and have been reading up on the internet lately.

    My question is, what is the main difference between ISO and EV?
    They both seem similiar controlling shutter speed and brightness of image.
    But how do you know which one to change in a given situation?


    (P.S sorry if i sound like a complete newb)

    Thank You everybody!
     
  2. usapatriot

    usapatriot Well-Known Member

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    The ISO is how sensitive the sensor/film is to light. A lower sensitivity means that it gathers less light than a higher sensitivity. Since the higher sensitivity gathers more light faster, you can use a faster shutter speed.

    A picture shot at 1/125 at ISO 100 is the same as a picture shot at 1/250 at ISO 200.

    The higher the ISO the more noise in pictures while the lower the ISO the less noise in pictures.

    EV means exposure value and/or it can also refer to the exposure compensation on a camera.

    An EV value of zero means that the camera has chosen the exposure by itself, if you add +1EV you are making the image one stop brighter, for example if you were shooting at 1/60 on auto setting, if the picture were to come out too dark you apply +1EV and the camera will then shoot the picture at 1/30 to let more light in. Same goes for making a picture darker by removing -1EV, the camera would then shoot the shot at 1/125 which would mean less light and a darker shot.
     
  3. Danny1911

    Danny1911 New Member

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    thank you so far, just one more thing please.

    so basically ev controls the shutter speed while iso controls brightness right?

    Also if the shutter speed ranges from say 1/2 to 1/1000 would that just make 1/2 +2ev and 1/1000 -2ev? or are there even more factors affecting it on a point and shoot digital camera?

    Thank you for your help so far with all these questions.
     
    Last edited: Jul 10, 2008
  4. usapatriot

    usapatriot Well-Known Member

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    Well there are a range of things that the camera could do when you adjust the exposure compensation to make the picture darker or brighter including adjusting the shutterspeed, aperture and the ISO.

    ISO controls the sensitivity of the sensor to light.

    I'm not exactly sure what you are trying to describe there but a shutter speed of 1/2 with +2EV applied would be turned into a two second exposure and 1/1000 with -2EV would be turned into 1/4000.

    Have a look at this article
     
  5. AKAJohnDoe

    AKAJohnDoe News/Review Writer News/Review Writer

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    EV is actually a set of possible exposure values (aperture+shutter+ISO) that all yield an identical result.

    For example, these settings all have approximately the same EV:
    • ISO = 100 & Aperture = f/16 & Shutter = 1/125
    • ISO = 100 & Aperture = f/8 & Shutter = 1/500
    • ISO = 400 & Aperture = f/16 & Shutter = 1/500

    There is a bit more detailed explanation here.
     
  6. Danny1911

    Danny1911 New Member

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    Thank you both for your responses. So ev can affect a couple things. Also i learned alot from the links to0 bad there is little manual control with my stylus verve. So basically all i can do if i want a faster shutter speed is change the ev. Anyway thanks guys.
     
  7. ajaynejr

    ajaynejr Active Member

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    Exposure value refers to a "quantity of light", which can be described using a shutter speed and an aperture setting.

    One stop smaller (F/4.0 is one stop smaller than f/2.8 and F/4.0 is two stop smaller than f/2.0) together with shutter open twice as long equals the same exposure value.

    Photographers define a higher exposure value number as a smaller amount of light for example EV14 is half as much light as EV13.

    Exposure value, if the camera lets you change it manually, will let you make the finished picture lighter or darker. Some semi-automatic cameras let you choose the EV while the camera still controls what aperture and what shutter speed will achieve that EV.

    Exposure compensation tells an automatic camera to deliberately use a larger or smaller EV than the light meter would otherwise compute for the exact same subject and framing and the sun did not suddenly go behind a cloud*. The scale you are given (usually -2 to +2) is such that when you choose plus, the camera increases the amount of light, for example if you choose +1, the camera forces an EV that is one unit smaller (whcih the camera usually does not tell you exactly). You change the exposure compensation to make the finished picture come out lighter or darker.

    ISO works the same for film and digital photography. When the ISO is set higher (digital) or film with higher ISO is used, then shooting the same subject requires less light (a higher EV numerically) to begin with. Changing the ISO on an automatic camera does not make the picture lighter or darker unless the camera was pushing its limit on lens opening and/or shutter speed otherwise.

    Generally, the higher the ISO, the grainier the picture, but often the camera is pushing its limits for shutter speed and aperture so you have to use a higher ISO.

    Digital camera hints: http://members.aol.com/ajaynejr/digicam.htm

    * This is a little confusing to explain. If you change the exposure compensation by minus one (to darken the picture overall) and then take a second picture, and the sun did go behind a cloud, then the automatic camera will compute a new exposure value for the obscured sun and do your exposure compensation choice on top of that. So the second picture's actual EV may be more or less than the minus one you chose. The picture itself will still look darker by one EV unit.
     
    Last edited: Aug 2, 2008
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