Aperture is one of the least understood camera terms, but perhaps the most important. An aperture is nothing more than a hole.  The size of the aperture refers to the size of the hole.  When cameras first came to be they didn’t have lenses, instead they had wooden boxes with a ‘pinhole’ that you’d put a piece of tape or your finger over and allow light to go through the hole and project an image onto the film medium.  The “perfectness” of the hole and the distance of the aperture from the film plane was what made the image it projected sharp vs. blurry.

Where most people have problems is visualizing the aperture being big or small in relation to it’s “f-stop” number.  Lets make this easy, the bigger the number the smaller the aperture/hole.   A F1 value on a 50mm focal length lens meant for a 35mm camera would be roughly 1 inch around.  A F22 value would be at the other end, and maybe 1/32 of an inch around.  F2, F4, F8, F16 would get progressively smaller from the 1 inch opening to the 1/32 inch opening.  You’ve heard the term “stopping down?”  This means that you’re increasing the F-stop (aperture) and at the same time closing down the hole/aperture.  The aperture/hole is formed by closing from 5-11 blades (each lens has a set number of blades, usually 7 or 9) leaving a opening in the middle.


How does it work?  When you’re looking through your viewfinder and composing a picture your lens will be all the way open.  When you take the picture the camera will automatically close the aperture down to the selected value for that instant of exposure.  If your shutter speed is 1/60th of a second, then your camera will close the aperture from say F4 (assuming it’s an F4 lens) to F16, hold it there for 1/60th of a second, and then open it again.  It happens so fast you can barely see it happening in the viewfinder of a SLR or DSLR.  You’ll only see it with a SLR or DSLR because these are the only types of camera where your viewfinder looks through the lens vs. a separate viewfinder window.  Older cameras would use a mechanical lever to pull the aperture blades closed, modern cameras use an electrical motor.

As a “general rule” the ‘wider’ the aperture the more light it lets in, and the softer (less sharp) the image.  The ‘smaller’ the aperture the less light it lets in and the sharper the images.  Smaller only makes the image sharper to the point of diffraction which is usually at about F11.  Smaller than this still lets in less light, but results in a less sharp image progressively as the aperture gets smaller.  Expensive lenses such as the Canon 85mm F1.2 lens ($1200) helps break that rule a bit, providing a still sharp image even wide open.  In comparison a 50mm 1.8 lens ($50) at F1.8 wouldn’t be sharp at all wide open.  A Canon/Nikon 300mm F2.8 lens (about $4000) is almost as sharp wide open (F2.8) as it is closed down, and these lenses are designed to be shot wide open using all the light they can.

For now it’s just important to be able to visualize the blades in your lens opening and closing the aperture at the time of exposure, and that the bigger the aperture the smaller the number (F1) and the smaller the aperture the bigger the number (F22).  AND, when you see a lens labeled for instance “Canon 200mm F2.8”, this means that the “maximum” aperture of the lenses is F2.8.  The minimum aperture will be in the specifications, but never the actual lens title/name.  This is because its much more expensive to manufacture a 85mm F1.2 lens (about $1200) than a 85mm F1.8 lens (about $400), or a 50mm F1 lens (about $1800) vs. a 50mm F1.8 lens (about $50).   Will a F1 lens take a better picture for $1800 than a F1.8 lens for $50?  All other aspects of the lens being equal (they rarely are) only if you need that extra light to capture that particular image.   Because a wider aperture lens is more costly to manufacture, the manufacturers will almost always make the entire lens of a higher quality as well.


The selected aperture plays a very important role in setting up your camera to capture a composition.  The aperture interacts with the ISO, Shutter Speed, Focal Range, and Focal Distance to give you a certain look or capability for the image.  We’ve already covered ISO and now Aperture, and in coming weeks we’ll cover the others and finally we’ll put them together in various ways to show you how to control the image you capture.