How do you get the silky effect you see on waterfall photos?

That usually requires a shutter speed of 1/4 sec or longer. Of course this will depends on the water flow rate so do experiment with different shutter speeds.

1)Set up your tripod. This is almost a must unless you can find a good support to subsitute for the tripod.
2)Get the proper exposure setting The idea is to get a shutter speed of 1/4 sec or longer. So I usually set the ISO to the lowest (ISO 200 for my Nikon D70) and I close the aperture down to f/16 or smaller. I also use an circular polariser. It serves to reduce the light by 2 stops and it also cut down a lot of light flare commonly found in reflective water surfaces.

Despite all these settings,  the shutter speed might still be too fast especially if the day is still bright.  In that case,  you may need to add on Neutral density (ND)  filters to further cut down the light.

3) Shoot and review If you are using a digital camera, shoot and review the shoots. Make changes to your shutter and aperture settings if necessary. Do bracketing if using film.

Have fun! 

Related posts:

1. Mini Lesson 1 – Aperture, Shutter speed and ISO
2. What mode are you in?
3. Landscape photography – Filters
4. M A N U A L
5. Take your Time 1 – Star Trails