Foto 101.2 – Aperture

Apr 16, 2009 by Matt Voran

I think Aperture is the one concept that stops people from getting over the hump when it comes to really grasping the basics.  Shutter speed gets all the glory and attention and is really the easiest to understand, so my feeling is that many people already get this and probably understand it even if they don’t know it.  Aperture is not as easy to understand, and in most “point-and-shoot” applications, it just really does not matter, shutter speed again takes precedent. People notice blurry pictures which are the result of combining moving subjects with slow shutter speed.  But they DON’T notice the intricacies of aperture settings and their effect.

Define “Aperture”

Okay, easy.  The aperture of a camera (actually its in the lens) is just a hole.  it is like the “eye” of the camera, its the first gateway to let light into the camera.  That light is blocked by the shutter until you release it of course.  Many people liken the aperture/shutter relationship to a water hose filling a bucket or pool.   Aperture is the diameter of the hose.  Its HOW MUCH water/light is coming into the bucket/camera.  The shutter is simply the gate that determines how long you have the water running, and thus how full the bucket/film gets. If you have a small hose you would have to leave the water running longer to fill a bucket than if you used a large hose.  A larger hose puts out more water so you don’t have to run it as long.  right?  okay good.  So to summarize, the aperture is an adjustable hole that determines the volume/amount/quantity of light into the camera.

So what?

Good question.  This is why aperture is so important yet often overlooked by amateurs.  Try this simple test, it sounds goofy but really, do it.  It will make the following explanation much easier to understand.

Take a piece of paper.  and punch a big hole in it. about the size of a quarter.  Does not have to be precise, just fold the paper in half and rip a half circle in it.  Now open up the paper, and peirce a very small hole next to that one with a pencil tip or something.  Try to keep it as small as the point on an ink pen.  Now, close one eye and hold the paper up to the other eye, looking through the large hole.  With your free hand, make a thumbs up and hold it about a foot away from your eye.  Focus on your thumb.  See how the background is totally blurry?  Now do the same thing but look through the tiny hole.  Notice how your thumb AND the background are in focus no matter where your eye is trained.   This is a perfect illustration of “Depth of Field” which many will abbreviate as DOF on sites like flicker, and other photography forums, articles etc.   Let’s disect the phrase as well.  “Field” refers to the “field of vision or focus” , and “Depth” is how deep that field is.  So when your looking through the larger hole (large aperture) your going to have a very shallow depth of field.  So only objects in a very shallow area/plane of vision are going to be in focus.  Things closer and farther away from that focal point, will be out of focus.   When you are looking through the smaller hole (smaller aperture) you will get a very deep depth of field, so much more from foreground to background, will be in focus.  Make sense?  Check out these two photo examples. In the first I used a large aperture of F3.5, and in the second I used a small aperture of F22.   See the difference?

Now you might be asking yourself, “did he say large was 3.5 and small was 22?”  Yes.  This is slightly confusing but not really.  Just know that the larger the “F-Stop” number, the smaller the hole/aperture. the real reason for this is because an F-Stop number is actually an expression of a fraction.  If you are mathematically inclined this makes sense to you.  If not, don’t worry about it, just remember.  Higher F-top, smaller hole, greater DOF.  Smaller F-Stop, bigger hole, shallow DOF.   If you are like me and you just can’t let it go until you really understand the math of this, read this. WARNING – It’s a really boring and scientific explanation.  Enter at your own risk.

Okay…. SO WHAT?

Gotchya,  so real world application, here we go.  DOF (remember what that means?) is an artistic choice, it is part of composition, its part of what makes a photo interesting.  It can be a matter of application. For example, in a portrait, you want the focus to be on your subject, the person.  So it makes sense, and looks better, for the background to be out of focus so that the eye is drawn only to the persons face.  On the other hand, if you are shooting an amazing landscape, you probably want to have EVERYTHING in focus, from the cool little cactus that’s two feet in front of you, all the way to the gorgeous mountain in the far distance.  So you need a large depth of field, which would be a smaller aperture, which would in turn be a high F-Stop number…somewhere in the range of F22 would work perfect.  Ansel Adams was the king of this.

Awesome, I get it.  Use little for portraits and big for landscapes.

Not so fast, first of all, its a matter of taste.  Do what you WANT to do.  What looks good to you?  Sure there are generally practiced methods because well, that’s what most people think look good, but don’t be afraid to experiment.  That is why photography is fun, and one of the best things about digital photography, the freedom to experiment.

Second, you may not always be able to use the F-Stop you want.  Why you ask?  Well because it directly affects your shutter speed settings remember?   If you use a very small aperture like F-22, your limiting the amount of light coming in, so your going to have to compensate with a longer shutter speed.  I will explain more about the relationship between the points of exposure in another post. For now, I hope that gives you a better understanding, and if you want to know more, here is a great link to check out over on “The Photog Formula”.