The trick that most online resources would preach you, in order to shoot long exposure images, is to use a neutral density filter.
Neutral density filters are made out of glass or other materials which have a special coating applied on them. This helps in holding back the light, in effect allowing you to use a longer than usual shutter speed and capture a blurred effect of the scene in front of you.
It is widely believed that long exposure photography cannot be done without using a ND filter. This, however, is not entirely true.
Alternative technique to using ND filter
This technique, known as image averaging or also image amalgamation, basically uses a series of images shot using slightly longer than usual exposures and then combining everything in a photo editing software.
The result is that while the main elements, the ones that are stationary in the image remain sharp, everything else – water, clouds, foliage etc. move around creating this blurred effect. That in effect makes the essence of a long exposure image. But while a long exposure image would require a ND filter this technique doesn’t.
What you need in order to make long exposure images using this technique?
Well, to start off I can say what you don’t need - a ND filter. The gear that you do need is a camera, a lens and a tripod. As an optional item you can have a remote shutter release / cable release too. The last item will help you to eliminate camera shake on top of the dampening that the tripod will already provide.
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So how does the technique work?
Theoretically the result of amalgamation of a number of normal exposure images shouldn’t have to be any different to a long exposure image. I use the word normal exposure, however each of these ‘normal exposures’ would be slightly longer but not long enough to be a really long exposure. Sounds like a confusing statement? I’ll explain.
Let’s say a standard or normal exposure for a scene is 1/15 second. A slightly long but not really long exposure is 1”. A really long exposure is something like 30 sec.
You are using a slightly longer shutter speed to capture a series of images and then combine them into a one single photo. In order words, you will get an average of all images.
One thing that you need to understand at this stage is that when you make a really long exposure, you are basically telling the camera to make an average of anything is happening over the period of the exposure.
That means as the water flows past or the wind makes the blades of grass flutter or sways the trees or blows the cloud in the background your camera is going to record everything and then make an average of the whole thing in the final image. This is the same as what image averaging technique doing.
The biggest benefit seems to be that you don’t have to spend any additional amount on buying expensive ND filters. Good quality 10-stop ND filters can cost you upwards of hundred dollars. Plus you will need several of them for the right effect in different lighting conditions. Instead of carrying several pieces of ND filters, filter adapters and holders you can use this easy to use technique.
The second benefit is invariably that the level of noise of the images is extremely low. Low exposure images have certain quantity of noise which are difficult to be removed using blur tool in Photoshop. Images tend to become softer as a result, something that is unacceptable. On the other hand with image stacking the result is significantly clean.