What is a ND Filter?
ND stands for neutral density. A ND filter looks like grey glass to the naked eye but has no effect on color balance. The ND filter reduces the amount of light that reaches the sensor. It’s used for taking longer exposures in daylight conditions. For example, you may want to blur the moving water in a stream or waterfall. But if it’s daylight, and you try to leave the shutter open for a few seconds you will end up with an overexposed shot. Use the ND filter and get that silky waterfall effect you’ve seen. It probably goes without saying, but you’ll have to whip out your tripod and use that.
The following photo is an example of the image produced after leaving the shutter open for 20 seconds in bright sunlight using a very dark ND filter (4.00). If a ND filter was not used the picture would be completely washed out (overexposed). This photo was taken by Alan Grinberg. Alan is an accomplished photographer and his work is supe. You’d be doing yourself a favor by checking out his Flickr photostream.
"Do Photographs Lie?" -Alan Grinberg
I was at the Pacifica Pier shooting the big waves…, and remembered the smooth looking water you can get with very long exposures. I figured this might be an interesting contrast to the sound and motion of crashing waves. I pulled out my Kodak Wratten ND 4.00 Filter (totally black to my eyes), and was able to extend the exposure time by 13 stops. The exposure here is 20 seconds, in bright sun! It was difficult to get a sharp photo, as some of the crashing waves would vibrate the ground…. –Alan Grinberg
Neutral Density (ND) filters have 4 main uses
- Use slower shutter speeds - especially with high ISO, to capture movement in subjects such as waterfalls, clouds, vehicles, people
- Decrease depth of field - allowing wider apertures to be used, which helps separate subjects from their background
- Decrease the effective ISO (above ISO 400) and allow it to be used outdoors in bright situations
- More easily photograph bright scenes like snow and sand which could cause overexposure
The ND filter adds effective f stops to your lens. That means that if you’re using fast glass, it’s not so fast anymore. But the ability to leave the shutter open longer without overexposing is nice to have, especially for landscape photography, and blurring a waterfall or the ocean waves.
Neutral Density factors
- ND.3 (exposure adjustment = 1 stop, reduces ISO 1/2)
- ND.6 (exposure adjustment = 2 stops, reduces ISO 1/4)
- ND.9 (exposure adjustment = 3 stops, reduces ISO 1/8)
- ND 1.2 (exposure adjustment = 4 stops, reduces ISO 1/16)
ND Filter Will Help Your 50mm Lens On a Sunny Day
Do you own a 50mm lens? The “Thrifty 50” is a good one to have. [Relatively] inexpensive and generally high quality, it can be a good walk-around lens, great for portraits, and can help you achieve that blurry background while keeping the subject in focus. But sometimes it can be a frustrating lens, because if you try and use it on a bright sunny day it’s hard to get a photo that’s not overexposed. The solution? Use a ND filter. It allows the shutter to stay open longer without overexposing, or “blowing out” the picture. You can pick one up from B&H Photo. They’re less that $100.
Related Blog Posts: Circular Polarizers, Thrifty 50
