Waterfall exposure time with Nikon d5100 [duplicate]

Question

Possible Duplicate:
How can I make good fountain/waterfall photos?
How do I make the water silky in water/beach photography?

yesterday I went outside my town, and tried to picture waterfall. On my Nikon d5100 (18-55) settings was:

Manual mode

ISO=100, Aperture=f/25, Focal length=18mm

I wanted smooth water on my picture, but when I set shutter speed 6 seconds I get too exposed? Maximum value of shutter speed was 1/5 of second, to get well exposed picture. I didn't get what I want, because water was not so smooth as I expected. Obviously I have a problem. For example, if you look this picture, exposure time is 30 sec, and picture is not too exposed. How he did this?

Answer 1

If you are shooting in daylight, your photos are over-exposed and you can't change setting (aperture or ISO), you have to use ND filter.

There is already a lot of answers for this like here or here.

Answer 2

There are two ways to take long exposure shots :

1) Shoot in mornings/evenings when there's not much of light outside.

2) Make use of Neutral Density filter, this filter will cut down the amount of light entering the lens, which will allow you to shoot on a bright sunny day also.