Pretty As A Picture - ISO

The next exercise from It's Overflowing's photography course is on ISO.
It took me a little bit to understand ISO. At first when reading her post on ISO basically all I understood was that the higher ISO settings capture more light than the lower setting, so I couldn't understand why you didn't simply always use the highest ISO setting. I sorta got that the higher ISO settings were supposedly more grainy, but I couldn't see any discernable difference in her photos and later when I was experimenting with ISO levels, I couldn't see any difference in my photos either. Totally confuzzled!!

Can you see any difference between the low and high settings??

 
It wasn't till I skipped forward to the next post on Metering that I understood better how to see the difference in quality between the higher and lower ISO settings. What she recommended doing was zooming in on the same area of the photo for the lowest ISO and highest ISO settings to see the difference in quality. I was pretty surprised at the result when I did this.

 

The clarity of the lower setting is pretty obvious when zoomed in! So I'm figuring that means that you should try and use the lowest ISO possible in whichever given situation you're in, but if you're not intending on enlarging the image or using high-res images than you'd probably be ok if your ISO is too high anyway.

Pretty excited to go onto the next part which is basically using all 3 of the previous elements (Aperture, Shutter speed & ISO) together in manual mode and using metering to balance the 3 together.