Saturday, February 7, 2015

Day 6: Tying It All Together

Okay - APERTURE controls two things: The amount of light that comes in and the amount of focus it gives us.
SHUTTER SPEED controls the time that amount of light comes in.
and
ISO controls the amount of light that is needed for a correct exposure.

So you have a decision to make.  What do you want to emphasize in your picture:

IF you are shooting a portrait, and you only want your subject to be in focus, pick a large aperture (f1.8).  This will give you a very fast shutter speed. (A/AV MODE)
If you are shooting a landscape and wish th show off the entire scene, use a smaller aperture (f22). This will give you a long shutter speed - so use a tripod. (A/AV MODE)
IF you are shooting a hummingbird and wish to capture it's wings, shoot with a fast shutter speed (1/1000 sec). This will open your aperture to let enough light in. (S/TV MODE)
IF you are shooting fireworks and want to capture the trails of light, use a long shutter speed (5 secs). This will close down your aperture to a tiny dot. Again, use a tripod. (S/TV MODE)

However......

IF you wish to shoot a landscape you would close your aperture to allow a tiny bit of light in and give you that large depth of field, so everything will be in focus, the camera will say, "Well, he's letting a tiny bit of light in here, so I better give him a long shutter so the shot is not underexposed!".  But here's the problem: .  You might set your A/AV to f22, and the camera will set the shutter at 1 full second to compensate.  But what if you didn't bring your tripod?  You need a faster shutter in order to keep the shot sharp and not blurry.
This is when you will need to adjust the ISO. The higher that number the less light the sensor needs to get the exact same exposure,  So in this case, raise the ISO from 100 to 800.  Now the camera does not need as much light and will speed up the shutter to be hand-holdable.




As an example -  say, a dog on his leash wagging his tail. What do you want out of this? Well, maybe a fast shutter so the wagging tail is not a blur. A large aperture so the dog is in focus and not Old Man Johnsons' barn in the background. So set the aperture at f-1.8 (remember, the lower that number, the less in focus there is), but that will allow a ton of light to come in, allowing you to use a very fast shutter speed for the tail. Because it is daylight you don't need a ton of light so your ISO should be ok at 100 or 200.
But suppose there were a bunch of deer in the field. You still want a fast shutter to get their wagging tails, but you want everyone of them in focus. So you adjust your aperture to maybe a f-22, but that would severely limit the light coming in, forcing you to use a much longer shutter to get a correct exposure. But you still want a fast shutter because of that whole tail issue. That's when you raise the ISO to 400 or 800, so the camera does not need as much light, allowing you to use the settings you wish.
Mind wrenching, isn't it? I promise you this will all make sense after thirty or forty years of practice.
Tomorrow, a better recap.....