What is an ND filter ?

A Neutral Density filter, as the word « neutral » implies, has not for function to change the rendering of your photos.

Its only function is to lengthen exposure time longer by reducing the amount of light reaching the sensor.

Why use an ND filter ?

Bokeh

A too sensitive sensor or high luminosity can cause overexposure at wider apertures because shutter time are not short enough.
A neutral density filter allows you to use your lens at its wider apertures and get this bokeh you’re looking for.

Blur and movement

Longer shutter speeds make moving object blurry, which is can be a desired effect in photography.

Make moving objects disappear

By allowing you to do very long exposure, a neutral density filter can make disappear moving objects.

How to choose an ND filter ?

Quality

There is no use for an ND filter that is not homogeneous or generates tons of flare.

Buying cheaper is not always the right option. Read reviews or buy a filter from a reknonwn brand (B+W, Cokin, etc) if you want to avoid bad surprises.

Intensity of an ND filter

ND filter, are classified by numbers indication how much light they block (ND2, ND4, ND8, ND16, etc).

if your camera doesn’t use a cell that go through the lens, you can get the correct exposure by putting the filter in front of your external posemeter sensor.

You can also do the calculation which is quite easy : the number is corresponding to the multiplier that you should multiply normal exposure time.

For example, if your exposure time is 1 second without your ND filter. You should multiply this exposure time by the number of your ND4 filter. Which in that case will be 4 seconds (1s*4=4s)

If you want to find the correct aperture for a certain exposure time :
Stop = log2​(Number on the ND Filter).

Graduated ND filter

A graduated ND Filter is a filter that is cut in two : a part is ND and the over is in most case UV or transparent.

There are useful when you want to avoid overexposing the sky without having to underxpose the ground (the ND part is used for the sky, the transparent part for the ground).

Lowest sensibility fo the sensor

Your sensor needs a minimum amount of light to capture an image. Even if it’s an extreme case, be careful of not going under that minimum by using an ND filter.

You can buy filters here :

You can also buy prints here :