Last article I mentioned what is a good brand to look for when thinking of purchasing an ND filter. ND filters are sold in different strengths, and different scales are used to measure this. Some use an NDxx number, others refer to optical density, and some refer to the light reduction in EV or ‘stops’. This article I found really helps to figure it out what density to use and when. Four of the best tips for choosing the best ND filter for your DSLR. Hope this article helps as it has helped me and there is a Cheat sheet you can download and take with you. Click here to read.