Understanding Aperture

1. What is Exposure?

Exposure is basically the AMOUNT OF LIGHT (controlled by the aperture) that is captured over a SPECIFIC AMOUNT OF TIME (controlled by the shutter speed). Is that clear?

So your exposure is the process of recording light onto your digital sensor (or film). Don’t make it more complicated than that: light recorded somewhere (digital sensor or film). THE END. Easy Cheesy.

2. What is Aperture?

Your aperture, or your F-stop, controls (along with the shutter speed which we’ll discuss in the next post so just throw that out of your brain for now before you get confused) how much light hits your sensor.
A lens’s aperture (fstop) is basically a hole (and we’re getting as basic here as is humanly possible) that opens to let in more light and closes to let in less light. Similarly to the iris in your eye, but if that analogy doesn’t work for you feel free to throw it on out. The larger the “HOLE” or aperture (fstop), the more light will hit your sensor, the smaller the “HOLE” or aperture (fstop) the less light will hit your sensor, capiche?
Seriously, try not to over complicate it.
NOW: I’m going to sucker punch you here and I’ll just apologize in advance. A HIGH aperture number (fstop) = LESS light being recorded on your digital sensor (or film) while a LOW aperture number = MORE light being recorded on your digital sensor (or film). Yay to the genius who decided upon that little gem of a system! Seriously, I’d be game for toilet papering his house . . . you just let me know the time and place and I’m there.
The TRUE apertures are as follows (called fstops):
There are third “stops” in between (just think of it as where the “hole”, aperture, STOPS to let in a set amount of light), your camera may or may not have these.
The best way to find out will be to crack your manual or flip through the aperture dial on your camera and see which apertures show up. If you get numbers like: 2.8, 3.2, 3.5, 4.0, 4.5, 5.0, 5.6 then you’ve got third stops to work with. If on the other hand you’ve got 4.0, 5.6, 8, 11, 16. . . then you’ve got the true apertures and no option for 3rd stops.
NOTE: your lens may not have numbers as low as 2.8 or it may have an aperture number as low as 1.2. Your lens isn’t broken, it’s just got more or less capacity to let in more or less light. . . The general range of most lenses are highlighted in blue above.
Last word about aperture: it is your aperture (fstop) that controls the depth of field in a photo (don’t hyperventilate. . . see below).

3. What is Depth of Field?

Depth of field is basically the amount of an image that is in focus. An image with a very deep depth of field would be an image where everything is in focus, while an image with a very shallow depth of field would have a lot of “fall off” or BLUR with only one segment of the image in focus.
**QUIZ: Does the image above have a deep or a shallow depth of field??
ANSWER: Shallow, because only the boy is in focus and everything else is thrown out of focus.
STOP! Before we go any further, I want you to have a steady grasp of the way your aperture (fstop) functions. So I have a couple of assignments below for those who are desperate to learn about manual settings. . . or simply want a refresher.
FIRST: Memorize the full fstops. Just commit them to memory. The end. You can do it! Here they are again.
SECOND: For this assignment you will need 2 objects placed on a flat surface 1-3 feet apart outside or in a well lit room. Pop your camera over to Aperture Priority and experiment.
Aperture Priority (AP or AV) will allow you to play around with Aperture and how it affects depth of field without having to worry about shutter speed, because in AP/AV the camera automatically selects your shutter speed for you depending on the amount of light available.
Once you’re in AP/AV, set your lens on the LOWEST POSSIBLE APERTURE (fstop) probably somewhere between 2.8-4.0. Focus on the object closest to you and take a picture. NOW, “stop up” to the next FULL fstop. . . you just memorized them, so it should be easy. Skip over the third stops. . . or don’t. It’s up to you. So let’s pretend that I have a lens that has a maximum aperture of 4.0. I’d start by taking an image at 4.0. Then I’d take the same shot at 5.6, then at 8.0 then at 11 then at 16. . . see how this goes? You’ll notice a difference in the depth of field. That’s the goal of the assignment: to learn how aperture affects depth of field.
Don’t be dismayed if your images are slightly dark. I’ve noticed that for the most part when you shoot in AP/AV images tend to be slightly underexposed. . . .