Aperture - ISO or sensor sensitivity, shutter speed and aperture are the three basic controls the photographer has over photo exposure. ISO controls how sensitive the sensor is, shutter speed controls the length of time the shutter is open during exposure and aperture is the size of the opening on the lens.
But aperture is much more that that as it effects the depth of field in an image. Depth of field or DOF is areas that are not in focus in an image. Every modern lens is capable of sharp focus at a single plane. Changing the aperture can change how much of the image appears to be in focus.
In photography, bokeh (originally /ˈboʊkɛ/, /ˈboʊkeɪ/ BOH-kay — also sometimes pronounced as /ˈboʊkə/ BOH-kə,Japanese: [boke]) is the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens. Bokeh has been defined as "the way the lens renders out-of-focus points of light".
Aperture is measured in "f stops". Smaller numbers mean larger openings. Such as f1.2 lets in more light and creates more out of focus area than say a f16.
Using Aperture Artistically
Too often beginner photographers seem focused on sharpness. Reading lens reviews endlessly looking for the sharpest of the sharp lens. Meanwhile professional wedding, fashion and portrait photographers invest in certain camera systems just to have certain lenses which produce amazing out of focus areas.
Sharpness in a photograph is often determined by a fast shutter-speed, a steady hand or tripod, more then the actual lens anyway. The sharpest lens ever produced hand held at a slow shutter-speed won’t produce sharp images.
Unless you are shooting sports, race cars or other moving objects, aperture choice is the most often used setting for artistry in photography. Aperture determines how much of the image you want to be in focus and how well you want to define the subject using selective focus.
"Photography isolates the world via an aperture and gives the photographer the means to see differently, to achieve a spontaneous vision that is direct and uncompromising." - Ellsworth Kelly
Aperture in Landscape Photography
A traditional landscape photograph typically strives for a deep depth of field from front to back so smaller f-stops (higher numbers like f/11 – f/16 – f/22) are used. Ansel Adams used a view camera and lenses with very small apertures such as f/45 and up to f/64 and even started a movement called the Group f/64. DSLRs lenses typically don’t stop down this far. Also such small apertures let in such little light, long exposures and a rock solid tripod are must. Some lenses create diffraction issues at their smallest apertures and you have to watch out for dust spots as the increased depth of field betrays a dirty lens or sensor.
Landscape images don’t have to always be created with front to back sharpness. Artistic use of shallow depth of field with landscapes should also be considered.
Notice how the subject of the images stands out from the background. If a shallow depth of field wasn’t uses, the clothespin or swing might have been lost in the background.
"When you narrow down your range and are looking through just that narrow aperture of the lens, the intensity of what you see is so much greater." - Michael Snow
Aperture and lens choice
The effects of aperture will differ from various lens choices. Wide angle lens (24 mm and wider such as a 17mm) will have greater depth of field through out the aperture range then telephoto such as a 100 mm, 200 mm or 400 mm.
Some wide angle lenses have such a deep DOF field that you can set it at f8 and not even have to focus because just about everything will be in focus. On the downside, its nearly impossible to get a bokeh background.
Long lens inherently have a short depth of field so you have to be extra careful to focus on the eye of a bird for example, but you get a beautiful soft background.
Close focusing lenses such as macro lenses working close to subjects will also have a very shallow DOF, sometimes as small as a few millimeters.
Type of camera will also effect the DOF effect as mirror-less cameras such as micro fourth thirds cameras or small point and shoot cameras have the lens closer to the sensor than a full frame DSLR so its harder to get extreme DOF using mirror-less systems.
"Light makes photography. Embrace light. Admire it. Love it. But above all, know light. Know it for all you are worth, and you will know the key to photography." - George Eastman
Aperture and Lens Cost
Canon sells a 70-200mm f/4 for $1099 and a 70-200mm f/2.8 for $800 more. Why? Because there are professional photographer who want and need that extra wide aperture and it cost more to make lenses with larger glass.
If you are a landscape photographer shooting at the smallest aperture possible, you don’t need to spend extra on the f/2.8 version. But if you are a portrait or wedding photographer wanting maximum boken, then the extra $800 is worth the price.
Article by fine art photographer Edward M. Fielding
Credits:
Created with images by nayukim - "Camera lens and aperture" • Alina Sofia - "Pastel pink roses" • Bushido Photo - "Nature Bokeh - Black and White" • PRECIOSA ORNELA - "PRECIOSA Candy™ pressed beads" • Jeremy Bishop - "Bride holds wedding ring"