What should you do in case you are shooting outdoors and the sun is so bright that, even at the lowest aperture, opening your camera light meter shows over exposure? In such a situation you should use a neutral density filter. The main purpose of a neutral density filter is to reduce the amount of light passing through the lens without hampering any other factors (see the picture below).

The ND filter or neutral density filter allows all colours and wavelengths of light to pass through it. The ND filter indirectly helps us to get the right exposure without the hassle of changing our shutter and aperture settings. It can be incredibly useful and an ND filter is included in the Canon Filter Set 46 U. Different ND filters have different effects on exposure. A 0.3 ND filter reduces light by 1 stop, 0.6 ND reduces by 2 stops and 0.9ND by 3 stops. Apart from reducing the exposure, ND filters also indirectly help achieve various other conditions that create more attractive pictures.

Decrease depth of field

A picture taken without an ND filter has a shallow depth of field, which means lesser objects in the frame are in focus. On the other hand, the depth of field is higher, and even the background is in focus, with an ND filter . This is because the ND filter decreases the light intensity, thereby allowing you to open the aperture more, and consequently decreasing the f stop, as well as decreasing the depth of field.

Use of slower shutter speed and high speed film
Since a ND filter decreases the light intensity, it allows shooting at a lower shutter speed and obtaining motion blur without worrying about over exposure. It also allows for the use of high speed film because the intensity of light is already reduced and high speed film can help capture fast moving objects.