Exposure time, aperture and ISO value

Today we talk about some settings on digital camera(can be aplied on film camera of course). First we talk about ISO value, if that value is bigger, than image will be more noisy. Ideea is to keep that value on the lower degree! To show you difference I use Canon EOS 400D, same image, first with ISO 100 and second with ISO 1600
ISO 100
ISO 100; Exposure 1/100 sec F16

ISO 1600
ISO 1600; Exposure 1/1250 sec. F16

So.. if we use a low Iso value image will be more clear ( not in that exemple - it not was focused right :P ). But in the same time we need a long exposure time, in that case, the light was enought , so i don't need a tripod, but sometimes we need a tripod. Noise can be reduced with some software, but.. not complete!
Now, exposure time...well, here is a trick, depending to light we use a big, or a lower exposure time. Digital camera have an indicator.
If indicator is on O that mean right exposure value, if is in right image is "burned" or over exposed; if it's in left image is under exposed.
Good exposure
good exposure
Over exposed
over exposure
Under exposed
under exposure
Aperture value give the depth of image, if aperture have a low value, that mean we have a big aperture. That mean F5,6 is bigger than F32. Big aperture give a low depth of image; low aperture, a big depth.aperture F20

Aperture F5

So, low aperture value mean first plane clear and background blur and a short exposure time, and big aperture value results a more clear background and first plane too but big exposure time.
Sorry if you don't understand! English in not my default language! Feel free to ask!

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