Article by- Chinar Tekchandani and Prithviraj Banerjee
An appropriate analogy to understand ND filter is to relate it with sunglasses that don’t change the colour of light. However, these sunglasses are for your camera and not your eyes. ND filter, also known as neutral density filter is a filter that decreases or modifies the intensity of light entering the camera. It is placed before the lens or dropped into a filter slot.
What does an ND filter do?
This filter is usually an important tool for landscape photographers. It comes with different densities of darkness, so the ND filters that we have currently are ND3, ND6 and ND10.
ND filter can have multiple uses. One of those uses involves the aperture and the other one involves the shutter speed.
- Aperture- Most of the time, more light is better for landscape photographers however sometimes, pictures clicked in broad daylight can appear to be over-exposed. This filter allows photographers to shoot their wide aperture lenses with apt amount of exposure. This permits shallow depth of the field and selective focus effects under very bright lighting conditions.
- Shutter speed- With ND filter, the amount of light entering the camera reduces. With reduced light, the shutter speed decreases. A slower shutter may cause hazy images of moving subjects in the field. This quality of ND filter can be used when you want to emphasize the movement of your subjects. Some of these subjects include waterfalls, fast-flowing rivers, vehicular traffic, etc.
The meaning of numbers on ND filters:
These filters have different levels of darkness or intensity. It’s easier to have an ND filter that tells you about the number of stops of light required to darken your exposure. Unfortunately, the filter factor or the optical density numbers are not equal to the number of stops by which the light is reduced. There are charts available online that you can refer to when you’re shopping for ND filters.
Another way to understand it is, for every stop of ND filter, you have to halve the amount of light entering the camera. When light is halved, you need to double your shutter speed to maintain the same exposure.
Below is a tabular form that shows how an ND filter affects the exposure time:
|Original Shutter Speed||ND Filter Stops||New Shutter Speed|
|1s||24||4096hr (170 Days 16 Hours)|
We have given below some examples of images with ND filters to give you a clear understanding