One of the troublesome aspects of taking long exposures is the possibility for light to reflect off surfaces during the long exposure and cause artifacts that are difficult to correct. This is termed ‘light leak’ and can occur from several sources. Here is how I address minimising the cause of light leak from each of these sources.
- Light leak through the optical viewfinder. The best way to prevent leakage through this source is to cover up the viewfinder prior to the long exposure. With certain camera brands such as canon and Nikon, the camera strap has a piece of rubber that slots into the viewfinder. If you do not have this option, you can use a piece of blue-tac or cover the entire camera with a dark cloth. I have used all three methods effectively.
- Leak through the side of the filter holder. Fortunately, the current iterations of NiSi filter holders block out most light entering in this manner. I have seen some photographers stick duct tape to the sides of the filter holder, however I find that using a dark cloth draped over the top of the filter (taking care that the cloth is not visible in your final image) works quite well and is more convenient.
- Any light that does get through will be accentuated by scratches, dirty filters and water droplets. Make sure that before you commence your long exposure, both the inner and outer surface of the filter is clean and dry as it can be.
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