Graduated Neutral Density Filter, also called as Graduated ND filter is one which has got two halves. First half of this filter will be a neutral density one and the second half will be a clear section.The main purpose of such a filter is to overlay the bright part of the picture scene into the dynamic range of the sensor. It is mainly used by landscape photographers. It is mainly used to correctly expose the brighter part of the picture scene, especially the sky. It helps in reducing the brightness of the sky and thereby helping the picture to be exposed correctly. They are available in different shapes and sizes.
Different Types of Grad NDs
Graduated Neutral Density Filter comes in two types
1. Soft Edge
2. Hard Edge
If you observe an abrupt change of brightness in the scene(one section more bright compared to other), then you can make use of the Hard Edge one. This will help in reducing the harsh light (additional brightness) from the extra brighter side. In this way the final photograph will look more pleasing.
If the transition from the brighter side to the darker side is smooth in the scene then you can make use of a soft edge Graduated ND filter.
How to use a Graduated ND Filter?
One can use these filters both with an SLR camera as well as with a point and shoot camera. In the case of a point and shoot camera you will have to hold it in front of the camera. For certain models of digital camera you may get some additional accessories, which will help you in mounting filters in front of the lens.
Image on the left side is taken without using a Grad ND filter, whereas the image on the right is taken with a 0.9 Grad ND LEE filter. Feel the difference.
For, SLRs you can directly mount it on your filter thread if it is a screw in type or you can connect the adapter and slide the grad ND filter, if it is a rectangular sheet. If it is a rectangular sheet then you can adjust the separation of the darker and brighter side. So, in my opinion it is better to go for the rectangular sheet type with the adapter.
The darker section on the filter should be placed for the brighter side and the other section for the darker side. In the case of soft edge filters there will not be a clear demarcation of these two sections, whereas in the case of hard edge ones; one can clearly see the separation. If you are interested in landscape photography, then better carry both soft edge grads and hard edge grads with you. Some of the well-known manufacturers of Graduated ND filters are Lee and Cokin.
When to use a Graduated Neutral Density Filter?
If the lighting conditions are not so good and you have got a highly bright section in your frame then you can make use of a Graduated Neutral Density Filter. When you are taking the photo which contains a bright sky then you can make use of this filter. This will help in reducing the brightness of the sky. Also, when you are shooting a sunset, you can use this filter to brighten the foreground artifacts.
Do not use this filter when the lighting is normal. If you add a graduated ND filter under normal light then the picture will look dull. Another thing is that, if the separation between the darker portion and the lighter portion is curved, then don’t use this filter. You can also use it indoors, to lighten the subject of interest and to darken the window.