If you decide you want to shoot a slower shutter speed to blur action, the bright sunlight will not allow for a shutter speed slow enough to blur the motion.
Another really good example of when to use a slower shutter speed is when you are shooting waterfalls in the bright sunlight.
Instead of capturing each individual drop of water, you may want to use the “misty” water effect. What this does is keeps the shutter open for a longer period of time allowing the water to “wash” over the camera sensor. This blurs the water and adds a smooth flowing feel to your image.
So, we have a problem, too slow of a shutter speed will overexpose your image, giving you bright white in the entire picture with no detail.
So, how do we fix this? The answer lies with the “Neutral Density” or ND Filter for your camera.
What is an ND Filter and what does it do?
An ND Filter acts as a barrier to light entering your camera, cutting down on the amount of light coming into the camera for the entire image.
With this barrier blocking the light, this means you can keep the shutter open for longer periods of time. When shooting waterfall images, this is usually 1/8th of a second or longer.
There are two types of ND Filters commonly used. One is a “graduated ND Filter, which is dark at the top, and slowly becomes clearer from top to bottom.
Graduated filters are used in large part by landscape photographers to capture those stunning views where the sky doesn’t overexpose and underexpose or make the foreground too dark.
The most common use for a graduated ND filter is to block out some of the light from the sky, allowing you to properly expose the foreground or front of your image. You can see the greens of the grass, and trees while the sky is partially, but not noticeably blocked making for a better picture.
The other type of ND filter is a full ND filter which evenly blocks all of the light coming into the camera equally, this type of filter is rated based on the amount of light it blocks, meaning you can keep your shutter open for much longer periods of time, even full seconds, allowing you more control over the image you are taking.
The key to successfully using an ND filter is experimentation, and if you are using an ND filter to take a long exposure, you should definitely have your camera on a tripod.
A graduated filter can be great for any landscape picture to help block out the bright sky.
ND filters are primarily used for the D-SLR cameras.
I could really get confusing with they different ratings on the ND Filter, but for now, I think it helps for you to know what they are and what they do.
Hope this helps.