This is a topic I have spent hours upon hours of research on. Back in January/February 2013 I took my camera to High Force waterfall, it was late in the day and the light was dimming. I wanted to capture that "misty, dreamy, milky water effect".
I set up my tripod and camera & using a long exposure (shutter speed) I snapped away. I got the odd half decent shot and was pretty happy with my first attempt. Roll on a few months later and I took my trusty camera to another waterfall, the light was really hard and it was right in the middle of the afternoon. I set everything up again & was really frustrated and just couldn't understand why the highlights "water" were so blown out.
Cue months and months of my own research! Cue ND Filters or Neutral Density Filters as they are also commonly known.
If you want to do this type of shot you are going to need to invest in a ND filter. They range in price dramatically and in strength. I recommend a 10 stop filter. These filters range from the Lee Big Stopper which has a hefty price tag to other manufactures such as Hoya, B&W, Hadia to name but a few. If you buy the screw on type you can also stack them on top to give more strength, you must bare in mind that you will see colour casts more often then none when doing this.As you will if you choose to buy some of the cheaper brands. Do some research and read reviews before you buy any cheaper filter is my recommendation!
I didn't really want to spend a lot of money and even the cheaper options still came in around £40-£50 which is quite expensive when you think it's just a bit of "black glass". I have read other people using welding glass as a cheaper alternative as well, if you want to go down this route?
I picked the Hadia, traditional "screw on" type filter. The Lee filter for example works differently and has a attachment you fit on the front of your lens. The actual filter then slides between the lens and the attachment piece.
This is the Lee Filter Attachment
This is the Lee "Big Stopper"
The images above show the unique way Lee cover this product range. Below is my 10 stop filter & as you will see it is much more you're typical traditional type filter.
You MUST make sure as always to purchase the correct size for your lens size. As your lenses most likely all have different dimensions it's probably best to decide which lens you are most likely to use for these style of shots before purchasing, otherwise you will have to buy several of the same filters for different lenses which would prove costly.
So you've done you're research and decided the best ND filter for you & now its time to use it! You screw it on you're lens & Eh?!? Its pitch black, you can't see anything? Right!? How are you going to see what you're taking the picture of???
Don't fret I've done the research and have the tips, so all you have to do is read on.....
Set up you're camera using a Tripod (this is a MUST)
Use Manual mode or Shutter Speed Priority Mode
Attach you're remote shutter cable or use the self timer if you don't have one
Now make sure you have you're ISO setting as low as possible 50/100 for example
Switch you're lens to manual focus & compose the scene and focus
Now expose the scene & take note of your shutter speed
Carefully attach the filter making sure you don't knock you're composure out or mess with your focus ring
Now you need the calculate what you're shutter speed setting should now be with the 10 stop filter attached which is also known as 3.0 or 1,000x. Therefore if you're correctly exposed scene was using a shutter speed of 1/400 you're new shutter speed with the filter on should be 2"5 seconds. The best tip I have is to download the ND CALC app on the app store or I'm sure google market have one too. There is a way of calculating this using you're brain, but I am useless at maths, and cant advise although it's probably very simple!
And voile! You should find you get some nicely exposed shots!
I always shoot RAW & take all pictures into Lightroom for processing. Any slight colour casts can easily be removed using your hue/saturation sliders.
Hope this is of help!
As always any comments feel free to ask!
Lots of Photography love