One of the most important terms you will hear on any photography related website or blog is camera aperture. Whenever you encounter a good photograph exhibited by a photographer, either in a gallery or in a magazine, chances are you will see a series of numbers alongside, describing the camera settings while taking that particular shot. One of those numbers, usually prefixed with the letter ‘ f ’ is the aperture setting.
So what does the term ‘Aperture’ mean anyway?
In the strictest sense, Aperture means a hole or opening through which light is allowed to pass. So a camera aperture is the hole in the front of the camera through which light is focussed onto the image sensor. Simple?
The best way to understand this is to compare a camera with the camera inside the human body, the eye.
The circled area termed aperture is the hole through which light gathered by the lens is focussed onto the image sensor.
Now, comparing the cross section of the human eye with the simple cross section of the camera, it is easy to see how closely the camera is designed like the human eye. In the human eye, the iris (pictured below) is a muscular ring like structure which opens and closes depending on the amount of light the eye senses. This opening, called the pupil (the dark hole in the centre of the iris), controls the amount of light entering the eye and falling on the back of the eye, the retina.
Similarly, in the camera, a diaphragm controls the size of the aperture, the hole through which light passes and falls onto the image sensor on the back.
What does the aperture do?
Just like the pupil in the eye, the aperture controls the amount of light falling on the image sensor. The larger the aperture, a higher amount of light is allowed to fall on the image sensor.
Adjusting the aperture allows the image sensor to record the right quantity of light to capture the subject perfectly. Too large an aperture would cause too much light to fall on the image sensor, causing the image to become very bright and white, a condition photographers refer to as a washout. 
On the other hand, too small an aperture causes the captured image to be under lit, in other words, much darker and low detail than the scene really is.
Making sense of aperture numbers
On a camera, the aperture settings are defined as f-numbers or f-stops. this is usually denoted as the letter ‘f’ followed by a number, e.g. f4.4, f22
Typically the f-number can be varied to any number, but practically this type of continuous adjustment is difficult to achieve given the mechanics of the lens. Hence, certain preset ratios have been identified and universally adopted in most lenses. These presets are known as f-stops.
The main f-stop numbers which are universally available in all lenses are a range between these numbers:
| f-stop | Relative Size | Used in situation to capture… |
| f 1.4 | Very large | Dark night landscape |
| f 2 | Large | Moon lit night landscape, stars |
| f 2.8 | Large | Night photos |
| f 4 | Medium | For most situations |
| f 5.6 | Medium | For most situations |
| f 8 | Medium | For most situations |
| f 11 | Small | Sun lit objects other than snow |
| f 16 | Very Small | Snow landscape, well lit white objects |
| f 22 | Very Small | Bright light, Sun lit snow |
These particular f-numbers are chosen as presets for a very interesting reason. When you switch from a f-number to the next f-number in this series, the effective amount of light falling on the image sensor is reduced by exactly half. So the aperture size at f5.6 allows half the amount of light to fall on the image sensor as compared to the amount of light the aperture size at f4 would allow.
Fixed lens cameras and point and shoot cameras would have a small range of f-stop settings, typically f-4 to f-8. The dSLR Cameras with interchangeable lenses do not have a aperture range of its own, it is the lenses that each have their own range.
How do you adjust aperture?
Almost all cameras today allow the aperture size to be handled by the camera. This way, a light sensor on the camera reads the light level in the scene, the camera figures out the appropriate size of the aperture required to let in the right amount of light. So you just set up your shot, the camera figures out the settings and depressing the button, you have a pretty picture.
Some cameras allow you to select the aperture size. This is done either digitally using a joystick or buttons on the back of the camera, or manually by rotating a ring on the lens. This gives a photographer better control on the amount of light falling on the image sensor and if necessary, allows him to be creative by deliberately underlighting a scene or slightly washing out the scene.
We will look at how the aperture actually affects the photo and how to use aperture in a future post. Until then, do send in your comments and suggestions.
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