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Exposure Tutorial Part One: What is Aperture?

February 19, 2012

This tutorial will be the first of three in a series on Exposure: “What is Aperture?”, “What is Shutter Speed?”, and “What is ISO?”  Members are encouraged to read them before our next sessions where we will go over camera settings and theory in more detail.  I know some people just want to be able to pick up the camera and have the camera take a great photo of their child, but that’s just not the way it always works!  I just read this quote by Ansel Adams the other day: “The single most important component of a camera is the twelve inches behind it.” So if you want to step  the quality of your photography up a notch, it’s time to do some learning!  Believe me, when I first started trying to figure out the exposure triangle (how aperture, shutter speed, and ISO work together to make a good exposure) I was overwhelmed.  I honestly thought I would never internalize it or understand how it worked.  But with reading, practicing, watching, practicing, messing up, and practicing, I think I understand it a lot more now, and it’s helping me grow in my photography WAY more than if I would have stayed in auto mode or portrait mode!  With the little bit of understanding of how the exposure triangle works, you will gain control over how your images turn out, and your creative vision in your head will be more likely to come out in your photos.  Are you excited?  🙂

When I first started using my DSLR, I used the creative mode of “portrait” most of the time.  I liked it because the camera would do the thinking for me, and it would make a nice blurry background in my picture, allowing my subject to pop against it.  It worked wonderfully—in great lighting situations, that was!  As time went by, and lighting situations weren’t ideal, I started realizing that I didn’t have the control over the outcome of my pictures the way that I wanted to.  At that point I started doing some reading and research.  I realized that in order to gain control over my pictures, I would have to stop blindly pushing the shutter and hoping the result matched my vision, and I would have to start “telling” the camera what I wanted it to do.  That led me to aperture priority mode (on your camera dial it shows as either A (on Nikon) or Av (on Canon).  Aperture priority mode allows you to choose the aperture that you want, and the camera will determine the other settings for you.

So what is aperture?  Why would you want to control it?

Aperture is the hole inside the lens.  The hole is made by overlapping blades.  The blades overlap and change the size of the hole as the photographer or camera adjusts the aperture number.  The number that you see on the front of your lens tells you the widest that your aperture will open up to.  For example on my kit lens 18-55, there are some numbers that look like this:

Kit lens aperture

The 1:3.5-5.6 means that when I’m zoomed out at 18 mm, the aperture will open up to 3.5 at the widest.  When I zoom in to 55 mm, the aperture will open up to 5.6 at the widest.  The lower the number, the wider the hole.  It seems backwards.  So, when you see a lens that is labeled say, a 50/1.8, that means that the widest the aperture can open up is 1.8.

Why would you want a wide aperture?  Well, the wider the opening, the more light comes into the camera.  If you have more light coming into the camera, you can possibly get away with not having a flash indoors, and/or you can have a faster shutter speed to stop action.  Additionally, and one of my favourite reasons why, is you can achieve a really nice blurry background.  If you have your aperture set at a lower number like 1.8 or 2.0 or 2.8  even 3.5, your depth of field (area in focus) is smaller.  That means that you can have your subject in focus, but the background blurred out.

There is a lot more to aperture than that, but this is just an intro.  So, if you want to explore your aperture priority mode, switch your camera’s dial to A or Av depending on the brand.  Set up a little experiment on your kitchen table.  Set up a few items in a diagonal line, one item close, one a bit farther back but to the side, and another one farther back, like this:

Once you have your items set up, change your perspective and get down to the level of the table.  You’re in aperture priority mode (A or Av on the dial) , so adjust the aperture to be as big of a number as possible—like 16 or 22 or so.   (you might need to look in your instruction manual for specific instructions on how to change the aperture…on my Canon T1i it’s done by rotating that black dial right between the shutter button and the ISO button.)  After you have changed your aperture to a high number, focus on the item closest to you (hold down the shutter button partway to focus and then once it is in focus, click the shutter).  You might get something like this, with all three items mostly in focus:

Then change your aperture to a smaller number (which means it is wider open). Here I opened it up to f/10. You’ll notice that all three cans are pretty much still in focus, but the orange crush is a bit blurry. That’s because the depth of field (area in focus) is getting smaller!

Then make your aperture number even smaller! Here I used f/5 (which means it is wider open than f/10 remember! And wider open means your depth of field—area in focus—will be smaller. Therefore, more of a blurry background!)

If you have a lens that opens up wider, like the “nifty fifty” which opens up to f/1.8, give that a go. See the difference??

There are other factors that play into how much is in focus and how much is blurred, such as your distance from the subject. But what is most important for you to remember are these points:

-Aperture is the hole inside the lens
-The smaller the number (e.g. 1.8) the “wider” open the lens is, and the more light comes in. We tend to use smaller f-numbers (wider apertures) for portraits because the background gets blurred out, and we can focus on the subject.
-The larger the number (e.g. 22) the more “closed” the lens opening is, and less light comes in. We tend to use larger f-numbers (closed down apertures) for landscapes or groups of people when you need to get more in focus.

We will talk a lot about aperture in the coming meetings. Do yourself a favour and play around with it…you won’t regret it!

Below is a cheat sheet on Aperture.  Fraser Valley club members will receive a copy at our March 1st meet up.  Friends from afar, here’s the 4×6 image in PDF form, Aperture PDF

Was this helpful? Any questions? Feel free to ask and we’ll do our best to answer.

~Posted by Sonja, MWAC host

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