Aperture/Shutter/ISO

Understanding ‘A’, ‘S’, ‘P’, ISO and How they Relate

The first time one holds on to a DSLR, one must wonder what do these alphabets on the dial, ‘A’, ‘S’, and ‘P’ stands for. For starters, here are what the alphabets literally means:

A or Av in some cameras is for Aperture Priority Mode

S or Tv in some cameras is for Shutter Speed Priority Mode

P is for Program Mode

Aperture Priority

Aperture is the opening of the camera lens that allows light to go through. Aperture size is represented by f-numbers or f-stops. The smaller the value, the more light is able to enter through the lens. For eg. Aperture value f2.8 will allow more light to go through than f5.6. Smaller f value = bigger opening.

In A or Av mode, you have full control of the aperture value while the camera automatically adjusts and sets the shutter speed to suit the conditions.

Shutter Speed Priority

Shutter speed represents the amount of time the shutter opens up in order for light to get through and onto the film or the sensor. The longer the shutter opens, more light will enter.  For eg. A shutter speed of 1 second will expose the film or sensor to light longer than a shutter speed of 1/50 second.

In S or Tv mode, you have full control of the shutter speed while the camera automatically adjusts and sets the aperture to suit the conditions.

Program Mode

Program Mode is selected when you wish for the camera to decide on its own the aperture and the shutter speed. Though you still have control over the ISO and exposure.

ISO

ISO refers to each camera’s sensitivity to light. The common range of ISO in entry level cameras are from 100 to 6400, while higher end cameras provide a wider selection ranging from 50-25000. Note that for most cases, the higher the ISO value, the quality of image will degrade due to grains or noise.

Making Sense of It All – The Relation

Some may get pretty confused with the individual explanation of aperture, shutter speed and ISO. But these three factors will greatly affect the quality of your pictures when applied properly.

Take one example - In dim lighting, a higher ISO setting (more sensitive to light) and a smaller aperture f value (bigger opening) is required to achieve a faster shutter speed to prevent motion blur.

There are so many different scenarios to illustrate the importance of these three settings. It’s best that you go out there and experiment them on your camera. Compare images taken with different settings and rest assured, it will make proper sense. Practice makes perfect!