why and when do you want to change ISO?

Shockey wrote in post #9391932
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

NO! Aperture does not affect the speed of light. Aperture affects the amount of light that reaches the sensor in a given amount of time (and this time is the shutter speed). Each full f-stop is a doubling or halving of the amount of light that can pass. For example, changing from f/2.8 to f/4 is a one stop reduction in the total amount of light that will hit the sensor if the shutter speed remains constant, therefore your shutter speed must double in order for the total amount of light to be the same as it was when shooting at f/2.8. So if you took a shot at 1/60 and f/2.8, you'd get the same amount of light hitting the sensor as if you shot at 1/30 and f/4. You won't get the same image, just the same exposure. A shot at f/2.8 will have less depth of field than a shot at f/4 and a shot at 1/60 will show less subject motion blur than a shot a 1/30. You need to read the tutorials on this forum for more info.

Those answers are clear... i guess my thought is that i set my iso to 200 and have never touched it.

really i knew what my answer was before i posted, but this cleared it up that there are times i will have to use it.

with my 50mm, i dont have to worry about ISO, but when i want to switch to my 55-250... i will eventually have to start bumping up my ISO.

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its actually been so long for me since i switched the ISO on my camera and thats why i never get the shots.

thanks for clearing things up!!!

jjaenagle wrote in post #9392061
with my 50mm, i dont have to worry about ISO, but when i want to switch to my 55-250... i will eventually have to start bumping up my ISO.

You must always be shooting in BRIGHT environments. Did you see my example? You could very well be getting 1/5s @ ISO100, f/1.8.

You've NEVER been in a situation where shooting with your 50mm and ISO100 gave you a blurry shot? You are VERY lucky!

Dont be scared to bump up the ISO a bit. It is a very usefull setting to be able to change.

The easiest way I can think to describe ISO is to say that it is the sensitivity of the camera. If you increase the ISO you increase the sensitivity of the camera.

This in effect gives you more light to work with and you will be able to increase shutter speed, use a smaller arpature or both. This will help you to reduce motion blur or to get a more suitable depth of field. (f1.8 can be a bit shallow sometimes)

The downside though is increased noise in the photo.

Chris

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

Sometimes referred to as the "magic triangle" or "golden triangle," this relationship is the most important concept in understanding exposure. Learn it. Understand it. Use it.

Shockey wrote in post #9391920
To simplify it:
Always shoot in Aperture priority.

If you can grasp the ISO-Aperture-Shutter Speed relationship, you'll quickly realize that always shooting in Av is not good advice. There are times when you want to control both aperture and shutter speed - handing control of shutter speed to the camera may not be in your best interests.

egordon99 wrote in post #9392075
You've NEVER been in a situation where shooting with your 50mm and ISO100 gave you a blurry shot? You are VERY lucky!

Lucky?!?!?!

That right there is my problem... anyways, im not saying it has never become blurry, but at those moments.. that is where i get confused and run out of ideas.

i either turn on more lights, move to something else, use a flash, switch to manually adjust my shutter speed......

BUT - I have RARELY thought about raising my ISO!!!!

i really need to just put a sticky on my camera to say, USE ISO!
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like i said, when i first started, i thought- high ISO = noise --- therefore - dont use high ISO

as you can tell, i am still new at this and really just learned a huge lesson from this thread--- dont be afraid to use ISO when i need to.

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I have just been putting myself in situations with more light that i dont need to use things like a tripod or higher f-stop etc...

shaftmaster wrote in post #9392056
NO! Aperture does not affect the speed of light. Aperture affects the amount of light that reaches the sensor in a given amount of time (and this time is the shutter speed). Each full f-stop is a doubling or halving of the amount of light that can pass. For example, changing from f/2.8 to f/4 is a one stop reduction in the total amount of light that will hit the sensor if the shutter speed remains constant, therefore your shutter speed must double in order for the total amount of light to be the same as it was when shooting at f/2.8. So if you took a shot at 1/60 and f/2.8, you'd get the same amount of light hitting the sensor as if you shot at 1/30 and f/4. You won't get the same image, just the same exposure. A shot at f/2.8 will have less depth of field than a shot at f/4 and a shot at 1/60 will show less subject motion blur than a shot a 1/30. You need to read the tutorials on this forum for more info.

Yes, you just said the same thing I said but in a bazillion more words