The most commonly used technique used for long exposures is setting the camera to make the image over 20 seconds. For this image I used a different technique called exposure stacking, to do it this way you make a series of photographs over an extended period and later blend them together in Adobe Photoshop.
The image above was created from 300 images captured over a 20 minute period and then blended together, I find this technique better than the conventional way of making long exposures as you can do it hand held and without filters and that makes it very flexible.
If you have any questions please feel free to add them to the comments below and I will get back to you ASAP.
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