why and when do you want to change ISO?

So i am wanting to learn more about photography! i still dont understand exposure and compensation completely and im sure i wont until i can get the education like most people have had... but i am starting now and here.

I have read "understanding exposure" by bryan peterson twice already and have remembered a little more and i'll keep reading it until i memorize it.

I still need some help with ISO.. i have tried this link but its not working right now http://www.digital-slr-guide.com/when-to-change-iso.html

can you guys simplify it for me? why do i want to go higher than 100, 200...
i just know that it helps in lower light situations but still dont want to bump it up really.

i know that ISO is an important part of it and i really have not been using it as much as i need to.

Iso 100 (low iso) for bright light with fast shutter speeds, for when you have lots of light like a sunny day. Use with large f-stops like f2.8.

Iso 800 (high iso) for darker scenes with slow shutter speeds, for when you don't have a lot of light.
Use with small f-stops like f14. Watch out for noise in the photos if you go higher, depending on camera and exposure of course.

Very simple explanation of course, hope it helps.

Shockey wrote in post #9391577
Iso 100 (low iso) for bright light with fast shutter speeds, for when you have lots of light like a sunny day. Use with large f-stops like f2.8.

Iso 800 (high iso) for darker scenes with slow shutter speeds, for when you don't have a lot of light.
Use with small f-stops like f14. Watch out for noise in the photos if you go higher, depending on camera and exposure of course.

Very simple explanation of course, hope it helps.

now im confused lol.... i get the iso part completely. maybe its all about using the f-stops?

I will ask that later in a different post as well, but if i am indoors, dont i want to use a larger aperture to get in more light? lets say i have my 50mm f/1.8 at a museum. no tripod.

If i set it to maybe f/8, it still shows a slower shutter speed. then i up the iso, and i still get a blurry picture because of shutter speed is still slow but not as slow as it was with low iso.

Now is it possible to change settings or is it just because i am being limited to what i have and should use a flash or tripod?

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when i am indoors, i always seem to want to use a larger aperture and vice versa when i am outdoors. I still am trying to learn depth of field as well, but i want to understand 1 thing at a time.

i plan on getting an xsi field guide and another photography book

There is a direct relationship between ISO, shutter speed and aperture.

If you increase your ISO from 100 to 200, leave your aperture set at the same value, your shutter speed will increase by 1 full increment. So... ISO 100, f/2.8, 1/60 will give you the same results as ISO 200, f/2.8, 1/125. Your depth of field remains the same, but the faster shutter speed allows you to stop motion more effectively.

If you increase your ISO from 100 to 200, leave your shutter speed the same, your aperture will change by one full stop. So....ISO 100, f/2.8, 1/60 will give you the same exposure as ISO 200, f/4, 1/60. In this instance, your shutter speed remained the same so you will have the same motion blur in both images, but because you have changed your aperture, you will have greater depth of field in the f/4 image.

I think maybe you have aperture confused. In your museum example you stated using a larger aperture in order to let more light in. A larger aperture is actually a LOWER f#. So in your example you would want to shoot at f 1.8 to let as much light in and to be able to keep your shutter speed high enough to avoid camera shake. I use the lowest iso I can get away with, providing that I can adjust my shutter speed or aperture accordingly. I only start increasing my iso when aperture alone isn't sufficient to give me a fast enough shutter speed in order to avoid camera shake.

Higher iso 800+ lets in more light so does a larger f-stop like f2.8 give you a faster shutter speed=less blurry pictures

If you use a small f-stop like f14 it lets in the light slower so your shutter speed slows down= more blurry pictures.

In bad light a higher iso give you a faster shutter speed.
So combine high iso and large f-stop for indoors in bad light for fastest shutter speeds.

Woolburr wrote in post #9391748
There is a direct relationship between ISO, shutter speed and aperture.

If you increase your ISO from 100 to 200, leave your aperture set at the same value, your shutter speed will increase by 1 full increment. So... ISO 100, f/2.8, 1/60 will give you the same results as ISO 200, f/2.8, 1/125. Your depth of field remains the same, but the faster shutter speed allows you to stop motion more effectively.

If you increase your ISO from 100 to 200, leave your shutter speed the same, your aperture will change by one full stop. So....ISO 100, f/2.8, 1/60 will give you the same exposure as ISO 200, f/4, 1/60. In this instance, your shutter speed remained the same so you will have the same motion blur in both images, but because you have changed your aperture, you will have greater depth of field in the f/4 image.

Hmm, I do understand that. For some reason my logic is off.

I have only been using aperture priority and time priority about 90% of my shots. i guess what i am doing is just not working with the ISO and aperture.

I have usually had the ISO set at 100 - 200 and sometimes up to 400. the other problem is that i dont change my aperture so often because i think, more light fast shutter speed.


and also, i think if i need slow shutter speed, then i change to time priority and set it to a shutter speed that i think is ok, ISO is still set too low, and aperture changes automatically.

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I bet some of you guys are laughing at me! it is no better than using the green box now that im thinking about it.

Maybe i will start shooting manual to make myself adjust things!
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Now that i said that... am i getting the basics of it? I know there is more to it, but as far as getting a correct exposure... how far off the tree did i land?

the exposure compensation confuses, white balance and other stuff confuses me but i want to be able to just get a correct exposure first.

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Im guessing a lot of my pictures are at the largest aperture possible with low ISO... and i just happen to be in well lit places all the time

crn3371 wrote in post #9391817
I think maybe you have aperture confused. In your museum example you stated using a larger aperture in order to let more light in. A larger aperture is actually a LOWER f#. So in your example you would want to shoot at f 1.8 to let as much light in and to be able to keep your shutter speed high enough to avoid camera shake. I use the lowest iso I can get away with, providing that I can adjust my shutter speed or aperture accordingly. I only start increasing my iso when aperture alone isn't sufficient to give me a fast enough shutter speed in order to avoid camera shake.

well, in that museum example, i would have used f/ 1.8 and low iso.... thats the problem cause i think every time im in low light, i need my aperture as wide open as possible...

i know that the the smaller the f/number the more light that goes through.

Shockey wrote in post #9391847
Higher iso 800+ lets in more light so does a larger f-stop like f2.8 give you a faster shutter speed=less blurry pictures

If you use a small f-stop like f14 it lets in the light slower so your shutter speed slows down= more blurry pictures.

In bad light a higher iso give you a faster shutter speed.
So combine high iso and large f-stop for indoors in bad light for fastest shutter speeds.

that helps... i think i have just been scaring myself that high ISO creates noise and i try to avoid it.

To simplify it:
Always shoot in Aperture priority.
Use your highest f-stop like f2.8 when you want fastest shutter speed, short depth of field.
Use to capture action so it will not be blurry, also portraits for short depth of field.
If outside use ISO 100 if bright, 400+ if it is darker or cloudy.
Inside use 400+ for faster shutter speeds.

Use a smaller f-stop like f14 when you want to a slower shutter speed, large depth of field.
For landscapes, non moving objects.
If outside use ISO 100 if bright, 400+ if it is darker or cloudy and you will need a tripod due to slow shutter speed.

f2.8 and f14 will let in the same amount of light, the shutter speed changes to allow this to create the same exposure.

F2.8 lets it in very fast

F14 lets it in very slow

Shockey wrote in post #9391920
To simplify it:
Always shoot in Aperture priority.
Use your highest f-stop like f2.8 when you want fastest shutter speed, short depth of field.
Use to capture action so it will not be blurry, also portraits for short depth of field.
If outside use ISO 100 if bright, 400+ if it is darker or cloudy.
Inside use 400+ for faster shutter speeds.

Use a smaller f-stop like f14 when you want to a slower shutter speed, large depth of field.
For landscapes, non moving objects.
If outside use ISO 100 if bright, 400+ if it is darker or cloudy and you will need a tripod due to slow shutter speed.

thanks! those are good ways for me to start and actually start for myself!

iso noise is better than motion blur

jjaenagle wrote in post #9391466
can you guys simplify it for me? why do i want to go higher than 100, 200...

Generally, you don't. The higher the ISO, the more noise. Sometimes, though, it's simply too dark to get the shot you're after UNLESS you increase the ISO. Then you have to start bumping it up. But again, the higher the ISO, the more noise.

That's why really expensive cameras (1Ds MkIII) have GREAT performance at high ISO. You have to pay for it.

jjaenagle wrote in post #9391466
i just know that it helps in lower light situations but still dont want to bump it up really.

Right.

Well said!

Shockey wrote in post #9391939
iso noise is better than motion blur

You're in a museum with your 50/1.8. You set the ISO to 100, Av mode @ f/1.8. The meter gives you 1/5s. That's too slow.
You increase the ISO to 200. The meter gives you 1/10s
You increase the ISO to 400, the meter gives you 1/20s
You increase the ISO to 800, the meter gives you 1/40s
You increase the ISO to 1600, the meter gives you 1/80s
You increase the ISO to 3200, the meter gives you 1/160s
You increase the ISO to 6400, the meter gives you 1/320s

Not sure how much clearer anyone can make it for you so hopefully that clears it all up.