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Thread: ISO Discussion

  1. #1
    Member Gecko Girl's Avatar
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    ISO Discussion

    Now what i need is something like this to help me with aperture and ISO! Will have to go searching the other threads to see if there is anything there.

    Mod note: Moved to its own thread from shutter speed discussion
    Last edited by Kym; 10-10-2011 at 5:38pm.

  2. #2
    Member fynpics's Avatar
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    Quote Originally Posted by Gecko Girl View Post
    Now what i need is something like this to help me with aperture and ISO! Will have to go searching the other threads to see if there is anything there.
    To answer your question Gecko Girl...

    APERTURE

    With aperture, all I remember is that aperture controls 2 things... the amount of light that gets into the lens and the depth of field.

    My understanding of depth of field is the measure of how much will be in focus in front of and behind the lens' focus point. So if say you focus on a person's face, the distance will be measured from there forwards and backwards.

    So if you are taking a portrait for example and want to only have the subject's face in focus and background/foreground blurred, then go for a wider aperture (smaller f/number).

    If you are taking a close landscape photo and want to have lots of different things in focus at varying distances from the lens, group shot or a portrait with a landscape in the background, then go for a narrower aperture (higher f/number).

    By increasing the aperture (or decreasing the aperture number, letting more light in) you will need to (or the camera will automatically) increase the shutter speed (keep the shutter open less to let less light in) to maintain correct exposure, as increasing the light by increasing aperture will overexpose the shot without some other compensation.

    By decreasing the aperture (or increasing the aperture number, letting less light in) you will need to (or the camera will automatically) decrease the shutter speed (keep the shutter open more to let more light in) to maintain correct exposure, as decreasing the light by decreasing aperture will underexpose the shot without some other compensation.

    ISO

    Now ISO, this relates to the sensitivity to light of the sensor (or the film for old schoolers), and the higher the number, the more sensitive. So if you are in a well lit place, say a sunlit situation, you can have the ISO down to say 100 or 200 for example.

    If you are in a darker place, say night shooting, and you either have the lens at maximum aperture and the shutter speed is still too slow, you might want to increase the sensitivity of the sensor. One good thing about increasing ISO is that it will be able to make the shutter speed faster and maintain correct exposure. One bad thing is that depending on the camera, sensor and settings, and how high you go with the ISO, you may introduce 'noise' into the shot, which to me looks like a specky distortion of dark colours.

    I haven't had a chance to post photos to show any of this, but this is my rudimentary understanding of aperture and ISO.

    The best way to play around with this is to get your camera and look at the calculations it makes when you change the settings say in aperture ('A' or 'Av') mode. Many people just take them for granted. Once you change the settings, have a look at how the camera compensates for the change that you have made to achieve 'correct exposure. For the extra daring, switch the camera into manual or 'M' mode and look at the interactions of aperture, shutter speed and ISO. In manual mode, you make the calculations... Experiment as to what you would have to do in certain conditions to get correct exposure.

    Any corrections or suggeestions are welcome. Hope it helps.

    Fyn-Pics

  3. #3
    Ausphotography irregular Mark L's Avatar
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    Good post Fyn-Pics.
    Gecko Girl, if you haven't had a look through the AP New to Photography section of the library, then these two links may be helpful:-
    http://www.ausphotography.net.au/for..._with_Aperture
    http://www.ausphotography.net.au/for...SO_sensitivity
    "Enjoy what you can do rather than being frustrated at what you can't." bobt
    Canon 80D, 60D, Canon 28-105, Sigma 150-600S.

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    Member Visions's Avatar
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    Fynpiks has it covered.

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    Ausphotography Regular swifty's Avatar
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    A minor clarification. For simplicity and to avoid confusion, ISO setting can be thought of as how sensitive the sensor is to light. But in digital that's technically not the case.
    There's only one sensitivity (the base ISO) and other ISO settings are manipulations of that base ISO.
    If for example base ISO is 100, when setting it to 200, the sensor didn't become twice as sensitive. The information is actually amplified twice as much instead.
    This is important because as well as amplifying useful info (signal), it also amplifies unwanted info (noise).
    Hence quality degrades as ISO increases although DSLRs these days are so good that the noise rarely is a hindrance until eg. above ISO 1600.

    In film, ISO ratings do indicate how sensitive the film is to light.
    Nikon FX

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