Switch to M mode…

Now it's you who poses. blender, closes og ISOAll three affect how light or dark your image will be.

The blender

The aperture, or diaphragm, is an adjustable hole that lets light into the sensor through a lens. The aperture has two properties:

Light quantity: The larger the opening, the more light reaches the sensor.

Depth of field: A larger aperture gives a shallower depth of field towards the inside of the image. A smaller aperture means that a larger area towards the inside of the image is in focus.

Aperture is shown as an f-number. Lower numbers reduce depth of field. Higher numbers increase depth of field sharpness.

The shutter

Shutter speed controls how long the sensor is exposed to light. It also has two properties:

Light quantity: The longer the shutter speed, the more light the sensor is exposed to.

Motion blur: Fast shutter speeds freeze motion, while slow shutter speeds blur everything that moves.

Shutter speed is measured in seconds, hundredths and thousandths of a second.

ISO

ISO (International Organization for Standardization) specifies the camera’s – or film’s, if you’re shooting analog – sensitivity to light. ISO has two functions:

Light quantity: The higher the ISO value, the more light is captured by the image sensor.

Image noise: The higher the ISO value, the more grain/noise in the image.

The rule of thumb is therefore to use as low an ISO as possible for as long as possible. When you can't use a longer shutter speed or open the aperture any further, the last resort is to increase the ISO.

The light meter “has the answer”

To know what settings you need – use the light meter.

The light meter shows whether the image is too dark or bright on a scale from left to right, with "enough light" in the middle. Set the aperture, shutter and ISO until the line is in the middle, then you have a good starting point.

And here is the cheat sheet. Good luck!