Aperture

“The opening in a photographic lens that admits the light.” Merriam-Webster’s Collegiate Dictionary.

A lens’s aperture has the same function as does an iris in an eye. It opens and closes to compensate for brighter or dimmer light. When a person moves from a darker to lighter space, such as inside a house to outdoors, the iris closes (makes a smaller opening) to limit light.

A human iris does its opening and closing automatically; the light meter is built in to a person’s brain and we do not have to calculate where to set it for optimum “exposure.” Many cameras have automatic exposure capabilities and set aperture and shutter speeds themselves. It’s when we enter the world of setting shutter speed and aperture manually that the creative fun begins; we are set free of the camera deciding for us what results it “thinks” we want.

Setting the aperture at “wide open” lets the most light enter through the lens. (Above, far left). Conversely, closing the aperture all the way (“stopping down”) restricts light from entering (above, far right). Most cameras with adjustable apertures have, on average, 6 or 7 f-stops.

F-stops? That is the technical term for aperture settings. It’s a term widely used by photographers and will mean more as we use f-stops. As you see above, f/2.8 is a larger opening than f/5.6, which is larger than f/16.

IMPORTANT: Each f-stop is exactly double or half of the f-stop on either side of it. A stop of f/8 lets in double the amount of light than f/11 does. A stop of f/5.6 lets in half the amount of light than f/4 does.

Shutter speed AND aperture. We get to compensate through the use of shutter speed and aperture. For instance, our light meter reading gives us a proper exposure of 1/125 of a second shutter speed at f/8. We could take our photo at that exposure and expect a properly exposed image. Everything is fine and we go off to get the film developed and see our result.

But, Fluffy the puppy we photographed romping through the back yard is blurry. The rest of the scene is not blurry, only Fluffy is blurry as she raced through our view.

The benefit of having both aperture AND shutter speed to play with is that we can compensate one for the other.

We would have gotten exactly the same correct exposure (proper amount of light) for that picture if it had been taken at a shutter speed of 1/500 of a second with an aperture of f/4. We would’ve “cut down” the amount of light passing through the shutter by 2 times (the shutter would be open 2 times less at 1/500 of a second than 1/125 of a second. From 1/125 to 1/250 is one “stop,” 1/250 to 1/500 is the second). Remember, each shutter speed is 1/2 or double the one on either side of it.

We would compensate for the faster shutter speed (losing 2 stops of light) by gaining 2 stops of light through a larger aperture opening. Everything would “balance” again because we’d turned one setting down and opened the other up.

DEPTH OF FIELD–

 

Study the two similar images above to discern the differences in focus.
In both instances the subject is in focus. The differences are in
the background blur/sharpness and the foreground blur/sharpness.
(Notice the leafy sapling directly below the model’s hand.
It’s blurry in the left photo, less blurry in the photo on the right.)

Depth of field, or how much before or beyond the subject is in focus, is directly related to aperture. The larger the aperture (opening), the shallower the depth of field. The smaller the aperture, the deeper the depth of field. Depth of field is a tool of great diversity to the photographer, whether it is to isolate the subject from the surroundings (above, left) or include more detail (above, right).

The photo on the left was taken at a shutter speed of 1/1000 of a second with an aperture of f/5.6. The photo on the right was taken at a shutter speed of 1/60 of a second with an aperture of f/22. Same exposure, different results.

Again:

 

These examples were photographed with a film camera. The photo on the left was set to the largest
aperture f/1.4 with a shutter speed of 1/2000 of a second. The picture on the right f/16 at 1/15 of a second.

 

The above pair of photos was photographed with a digital camera set to “manual” mode.
The image on the left was f/3.2 (maximum wide); the right was f/8 (maximum).

Activity:

Practice taking pictures showing different depths of field. Try shooting the same scene, making sure there are objects close to the camera and in descending distance from the camera (as in the floral images above) so you can see the effects of different aperture settings and what happens to the focus.