Long exposure photography in a nutshell is using a long duration shutter speed. Often it causes lights to streak, clouds to blur, and it is the main technique used for light painting. These are some long exposure photography tips that I have picked up along the way.
1) The most important thing for long exposure photography is to have a stable platform for your camera. A good tripod is a must for long exposures. The more stable the better.
2) Find something in your composition that will be rendered sharp. This will contrast with the blurry parts of your image. Often in landscape long exposure photography, the clouds will be moving at a rapid pace, try to focus on something stationary like a building, or an interesting stationary foreground.
3) Use a shutter release. Many shutter releases will have a timer that you can set for the exposure length. If you have a smartphone there is an app available that will act as a shutter release. It's the trigger trap. The app is free the hardware is $30. It will also help with time lapse photography.
4) Calculate your exposure. There are calculators you can buy to help you with this, but normally I do the math in my head. I will start at my 30 second exposure mark with the lowest possible ISO. Most cameras will only expose for 30 seconds unless in bulb mode. So when I see that my camera will properly expose an image for a 30 second exposure in aperture priority, I will then calculate how many stops I need to get to, lets say, 4 Minutes. I will then switch to bulb mode. My camera is set up to do 1/3 of a stop increments in aperture priority, so I know that closing my aperture down by 3 clicks will equal one stop. So from 30 seconds to 4 minutes is 3 stops or 9 clicks on my aperture adjustment wheel. This will give me a properly exposed image at a shutter speed of 4 minutes. Granted the light will have to be low to use this technique. It is often best to use this method at dusk or dawn.
5) Use a ND filter. There are many ND filters available in today's market. Some vari-ND filters can go from 2 stops to 8 stops, but my favorite are the 10 stop filters. They are less expensive with not much trade off, at least in my workflow. With the vari-ND, it is much easier to fine-tune your shutter speed, it is also easier to focus. The 10 stop filter, will require focusing before screwing it on the lens, and will also require some math. Set up your desired camera settings and make note of your shutter speed. Lets say it is 1/2 sec, then add 10 stops for your filter. If my calculations are correct, it would be 8 minutes. Set your camera to bulb mode and set your cable release to 8 minutes. You should come out with a decently exposed image. The pain of the 10 stop filter is that you will have to remove the filter if you wish to recompose so you can focus. In my mind that is not a bad thing. It will make you think more critically about your compositions.
Long exposure photography is fun and can produce interesting imagery. Some of my best selling photographs are that of long exposures. This week's image is the Frankfort Lighthouse in Frankfort, MI. I used a shutter speed of 4 minutes to blur the fast moving clouds and give the water a glass like appearance. The textures and mood of the long exposure made the otherwise lifeless morning come alive.