A Quick Guide To Understanding ND Filters

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If learning to expose correctly wasn't hard enough, getting around ND filters could be a nightmare if you don't have the correct guidance.
There are several brands and styles of ND filters, and here quality matters because they become the front element of your beloved lenses. Therefore, if you use poor quality ND filters, the light passing through your amazing expensive lenses will be degraded.
I still regret spending some money in my first years of photography on inadequate filters. All I wanted to achieve was that beautiful eerie look of silky clouds and skies, but I only knew that they were achieved via long exposures and some filter screwed in front of the lens.
I bought a circular polarizer, which is intended to be used in other circumstances; they are designed to reduce brightness on highly reflective surfaces not to reduce a substantial amount of light. The filters that are engineered for that are ND filters, and it took me a lot of time to discover that.

Photo by Shaun Mills on Unsplash
Something that you need to remember is that light is measured in stops of light, and ND filters are designed to reduce a certain amount of them.
The problem is that manufacturers haven't got their stuff together and present them in different units. I've created the following conversion table for you to understand better what each grading means:

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ND Conversion Table
Back to my story, after some struggles I got some ND filters in my hands, the problem was that the strongest grading I could find only allowed me to reduce light entering my camera by 3 stops of light and the results weren't as flattering as I wished them to be.
Finally, a friend of my mine loaned me an ND filter that allowed me to reduce up to 10 stops of light. The big problem was that I was rushing, and framing (from composition to focusing) isn't that easy to do if you can't see a thing.

Photo by Paul Morris on Unsplash
Long exposure photography should be considered an art by itself because thinking about grabbing a slice of time in the form of an image is really poetic.
My only advice for all you curious and passionate photographers reading us today is to go out there and practice a lot, every day, if you want to master what long exposure photography is all about.
There are plenty of resources out there, but I think this short yet deep guide is really comprehensive and right to the point, consider checking it out if you wish to know more about what long exposure is all about.

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About the author

Federico Alegria

Federico has a decade of experience in documentary photography, contributes some free images to the community and is a University Professor in photography. You can get to know him better here

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