Little more clarity on ISO?

In digital photography, I now have some basic grasp of how shutter speed and f-stop works... the answer I received for the ISO and how this correlates with this, however, I couldn't quite figure out. If you look on my profile for questions I've asked previously, maybe it could maybe help you explain it... the whole idea of the two being like a staircase (shutter speed and appeture), seemed to make sense, to me anyway. ^^; Yes, so please help me understand ISO and how this works with the appeture and the shutter speed and the whole mathmatics of it. Much appreciated. I have a digital photography exam in two days. :s


Okay, maybe I need to clarify a bit more... what is the correlating ISO numbers that directly correspond with appeture and shutter speeds to create a correct exposure? An F stop of 5.6 with a shutter speed of 1/60th of a second (I think) is a correct exposure, but what ISO setting would make a correct exposure with these two in combination? Would it be an ISO of 100 with an appeture of 5.6, and shutter speed of 1/60th? ISO of 200 with an appeture of 5.6 and shutter speed of 1/60th, etc. ?

Update 2:

Oh, and could you make it into a chart, if at all possible? ^^; That would really help me a lot. Thanks.

4 Answers

  • Anonymous
    1 decade ago
    Favorite Answer

    ISO is a measure of sensitivity to light for (silver based) film. If at ISO 100, a combination of f/8 and 1/125 sec shutter speed gives correct exposure, this becomes f/11 for a ISO 200 (double the ISO number) or f/8 with 1/250 s shutter speeds. In digital cameras, the ISO equivalent is used to measure the sensitivity of the sensor in comparison with what a filme based camera would require. SO higher ISO values - more sensitive to light. ISO 400 or 800 is pretty sensitive for film and allows shots at night or indoors without flash. Most consumer digital cameras don't do so well in low-light situations. Good luck on the exam.

  • 1 decade ago

    Well, if you want to use your staircase analogy...low ISO is less sensitive to light, high ISO is more sensitive to light. Essentially, ISO is *where* you start on the staircase.

    At a high ISO, you're going to be at a faster shutter speed/smaller aperture (I guess this would be on the upper part of the staircase for you); while in the same light, a lower ISO would be a slower shutter speed/wider aperture (you're at the lower end of the staircase).

    Essentially, if you hold the light constant, changing the ISO simply affects how sensitive your sensor is to light, affecting what shutter/aperture combo you get--so where you start out on the staircase, which will affect how you adjust the exposure (going up or down your staircase).

  • V2K1
    Lv 6
    1 decade ago

    Your assignment is to fully saturate a sponge with water (make a proper exposure).

    >> You can change the diameter of the hose (aperture).

    >> You can let the water run for a short time or a long time (shutter speed).

    >> You can change the rate at which the sponge sucks up water (ISO).

    Hope this helps.

  • Elbert
    Lv 7
    1 decade ago

    EDIT: Go to a book store and buy Understanding Exposure by Brian Peterson. It's a really easy to understand book on getting the right exposure using different Aperture, Shutter speed AND ISO settings.

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