Photography Lesson #2 Aperture or f/stop

Photography Lesson #2 Aperture or f/stop

Aperture refers to lens openings or a hole that opens up to let light into the camera. The smaller the f-stop or aperture number (say f/1.8, f/2.2 or f/3.2), the larger the lens opening is to let light in. So the larger the number (f/18, f/20 or f/22), the smaller the opening is.

The thing to remember about aperture is that the lower numbers give you less depth of field (or more blur) in the background and the wide open or higher numbers give you more depth of field (or less blur) in the background. So if you are shooting mountains you will want higher numbers. If you are shooting a child’s face you might want the lower numbers to blur the background.

Also the farther you are away from your subject the more depth of field you automatically have. So if you are shooting a football game from the stands with low light, go ahead and use a lower f-stop number to add more light into the scene because you are far enough away from your subject to still get clear shots. At 15 feet away, a child’s entire body will be in focus with an f-stop of 2.8, but if you move in closer to his face looking down and only couple of feet away, his face will be in focus but his body will be blurred. If you get really close you can have one eye sharp and one eye blurry.

Different lenses give you different f-stops. Fixed or prime lenses (that don’t zoom) are typically sharper and can give you lower f-stop numbers. My 85mm 1.8 lens will stop all the way down to f/1.8. My zoom 24-105mm will only stop down to f/4. So your ability to get more blur in the background also depends on what lens you have.

This picture of Joseph is shot with an ISO 400, f/1.8, and a shutter speed of 1/400. He is facing my south family room window with the front door behind him. Notice you can't even see the door because of the blur. There was a light blur in the upper right corner that was my front room window but I photo shopped it out. Notice that his arm is blurry because it is a little farther behind his face, where I focused.

Most point and shoot cameras have very little ability for less depth of field or blur, but they will give you great focus and distance shots.

Assignment: 

Set your ISO and then put your camera on A or Av which means aperture priority. This will let you pick the aperture and the camera will do the shutter speed. Set it to the lowest f-stop or aperture number. You will want a subject that is basically stationary for this assignment, a posing child or an object and you will want good lighting. Early morning or evenings are the best light in which to take pictures outside. Or if you want to do it inside, place your subject by or facing a bright window. Place your subject with some kind of background and move in close. You will want to focus on the same spot each time you take a picture. Then take a picture and write down in your notebook the ISO, Aperture or f/stop and the shutter speed. Move the aperture up a stop and take another picture and so on until you have taken pictures of all the f/stops on your camera and recorded them all in your notebook. You will see the background come into focus as you move your aperture or f/stops up. Post 2 or 3 of your favorites on the blog.