The grand finale of the triangle is ISO.
If you ever shot a film camera, you might remember that each roll of film had its
own ISO. This represented how sensitive that film would be to light, and that's
what you were stuck with for that entire roll.
Luckily now, we can adjust the ISO in camera, for each shot if we want. ISO can
be a tricky topic to cover because every camera handles ISO differently. For
example, my Nikon D750 produces really high quality images at a higher ISO
while my much more expensive, Nikon Z7ii struggles above 2000. The result is a
lot of digital noise, which does not look good! It's your job to get familiar with your
camera body and any such quirks.
The ISO is normally my last resort when trying to lighten an image, but my first
stop when toning down an overexposure.
So adjusting the ISO is an easy way to brighten or darken your image, but if you
go too high, you will see a decline in photo quality, sharpness and clarity, with
added grain and noise. Somoetimes the ISO is your option option when shooting
in very low light, and when that happens, just embrace the grain. So when I'm
shooting and my image is over exposed, or too bright, and my aperture and
shutter speed are OK, my first stop is to turn down the ISO, because the lower
your ISO the sharper your image.