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12-26-2009, 12:38 AM   #1
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ISO Help

Hi i was just wondering about the word ISO, what does this mean i am new to DSLR Photography and i just purchased a Pentax Kx And i was just wondering if anyone can tell me about ISO, how to use it and what does it mean.


12-26-2009, 12:46 AM   #2
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I don't know what ISO stands for from word for word (Although I could easily Google it right now if I weren't so lazy). But what I do know is that as you increase ISO, your sensor becomes more sensitive to light. As it becomes more sensitive to light, the picture quality tends to decrease due to noise. Noise are grainy dots in your images that don't look pleasant to most people who want to get the most clarity out of their picture.

People increase ISO so they can use a faster shutter speed. People tend to increase ISO at night time so they won't get blurry pictures from a slower shutter speed. I don't know the exact terms in the dictionary implying for shutter speed either, but what I do know is it is how long your sensor is exposed to light. With a higher ISO setting, you can decrease the amount of time your sensor is exposed to light. It is a trade-off, you sacrifice image quality with the expense of having a faster shutter speed.

Typically when it is darker, it is more practical to increase ISO. But if you are shooting still subjects such as buildings and automobiles, you could get away with using high ISO by using a tripod or flash. Using a tripod allowing you to minimize as much noise as possible while using low ISO and slow shutter speeds. Using a flash allows you to use the lowest ISO settings while still maintaining a good shutter speed, allowing you to shoot low light using low ISO without a tripod. At the same time though, the light from the flash is limited at a certain distance, depending how powerful it is. Therefore you will need to increase ISO to allow your sensor the capture more of the light at a further distance due to it's increased sensitivity to light. You can also decrease shutter speed to capture more light. I also think if you use a faster shutter speed with flash, it tends to decrease the distance it captures the light.

Aperture also plays a bit in it too, the smaller the aperture number is, the larger the opening. If you are using a aperture of f/2.8, it allows more light to enter your sensor than it would at f/5.6, allowing you to use lower ISO and still maintain a better shutter speed. At the same time most and if not all fast lenses tend to be sharper when they are used at a larger aperture number, which lessens the opening of the blades.

If you really really want to learn, I recommend you experiment for yourself because there's no better way to learn. I also recommend avoiding the full automatic mode if you want to learn. The best way I learned is by using manual, completely full manual. You'll learn a lot faster using manual than you would with using automatic, scene modes, aperture priority, shutter speed priority, etc.

Last edited by LeDave; 12-26-2009 at 01:00 AM.
12-26-2009, 01:01 AM   #3
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Welcome to the forum.
LeDave has given a good response, but if you're asking this sort of question I would suggest you do some reading on the basics of exposure:
12-26-2009, 03:29 AM   #4
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Not that it matters but ISO stands for: International Organization for Standardization
Its just saying that they are internationally defined standards for light sensitivity.

12-26-2009, 06:27 AM   #5
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ISO means International Standard Organization. Before ISO, we had ASA, which was American Standard Association and DIN, which was Deutch Industry Normalization. Note that ISO took the ASA standards as the norm. The DIN standard doubled the sensitivity of the film with every three steps, i.e. from 21 DIN to 24 DIN would amount to ISO 100 and ISO 200.

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