I was amazed, many years ago, after reading a Popular Photography magazine article. The photographer/author set up his camera on a tripod to point at a popular entry stairs to a New York subway station. He said that the shot was taken at peak subway hours yet the resulting picture showed no people just the image of the subway entrance. How could this be done? It seemed like magic.
I don't remember the details of how he did it but the trick was a very long exposure so that people walking by did not register on the film. He used an extremely small aperture, lowest film speed possible and maybe a pin hole or some form of "light blocking" filter so that the image took a long time to burn into the film. Thus the people walking by became invisible to the camera! He probably had the shutter open letting light in for several minutes. Compare this to the typical snapshot of 1/100 of a second.
Well, long exposures are still alive and well today, especially in landscape photography. Long exposures make water do wounderful things. The classic waterfall blur effect. You can also get a surface glass effect that can be very attractive. Sometimes, with more ocean like conditions you get smoky blur looks. Clouds can also blur into interesting formations if they are moving. Many looks are possible.
This article will show you some examples and tell you the process I'm using. Let me make you aware right up front, that you can't do this technique without a tripod. OK, lets have a look at an image I shot of the Virgin River near Zion Park in Utah; what you see here is what came out of the camera, no filters or Photoshop tricks. (click on for larger):
I was standing on a big rock jutting into the river with my tripod rather dangerously set-up on a very uneven surface. It was close to sunset and cold and windy. I framed and focused the shot carefully on my 5D. Then I took out my special B+W "10 stop light blocking" filter and carefully screwed it on the lens trying not to move anything. (Push the lens in and you change the focus) Now, both the viewfinder and LCD viewer on the camera back show nothing! Yes, because the light is blocked. Thats why you have to frame and focus before putting the filter on. I had already set my camera's shutter to "B" for manual control. I then had the inexpensive Canon wireless remote in one hand and my iPhone with timer app booted, in the other. (Some cameras have a timer built in that works with B so you don't need anything extra). Next I decide on an f11 aperture so eveything should be sharp (24mm). Now I look at the light and take a guess and how long to expose? (You can get table for this but I like to try learning it myself). So I opened the shutter with the remote, hit the timer button and decided to try 3 minutes. After 3 minutes I hit the remote button to close the exposure then wait while the camera processes the image (another 3 minutes). Ooops, overexposed! Try agin, this time a little closer but not right. Finally nailed it at 91 seconds. By this time my butt is freezing and I call it a day. But I'm happy because the image on the LCD looks amazing. Look at that glass water!
Later, back at home looking at the image reality sets in. Of course, long exposure means that anything moving blurs. This is what you usually want for water and sometimes clouds but in this image I'm not really happy with the trees along the river. I decide to stylize them with some kind of painterly effect. So now I have:
Most people so far like this version best but others prefer the original. I like this version. (or maybe the next)
Let me show you the ND filter that blocks the light:
The filter is covering a 100watt light; shows you how dark it is.
My guess exposure method can sometimes be tedious. To be more accurate you can use a spot light meter, especially if you are shooting the near dark. It needs to one that you can dial in a 10 stop exposure compensation such as this one:
This is not a cheap meter and I can't afford one just for long exposures so I guess. You can shoot long exposures anytime during the day to get interesting effects although most of these exposures are taken in low light conditions like sunrise/sunset/night scene. If you are shooting during the day, there is sometimes enough light in the live view on your LCD to frame and focus (if you can zoom in to see things accurately). For more information on how to use a meter and other useful tips re long exposures I recommend Mark Hilliard Ateliers article. Lots of good stuff on his blog.
To conclude I put together a slideshow (PDF so free Acrobat Reader needed) with example images that includes the exposure time, aperture value and ISO. These images illustrate various effects you can get with long exposures; I hope you agree that this is a very worthwhile landscape technique! Give it a try...