Photography - A brief look at the naming convention for Neutral Density filters

A brief look at the naming convention for Neutral Density filters

May 05, 2018,14:26 PM

The two main reasons to use a ND filter are when you want to reduce the depth of field and/or blur motion. This is done by reducing the amount of light that reaches the film or sensor so that the photographer can adjust the shutter speed and/or f-stop to achieve the desired results. As the name implies, we want to reduce the amount of light in such a way that all colors, all wavelengths remain 'true'... a neutral density filter.

The notation for Neutral Density filters is a way to indicate the relative amount of light that passes through any given ND filter. In simple terms, one step (or stop) in photography is halving or doubling the amount of light that falls on the film or sensor... thus starting from an unfiltered state the ratios for incremental reduction in steps goes something like this: 1, 1/2, 1/4, 1/8, /16, etc. Thus a "0 step" ND filter would allow all light to pass, a one step ND filter would allow 1/2 of the light to pass, 2 steps when 1/4 of the light gets through, etc.

A word about optical density... spoiler alert, photography loves logarithms. As expected the density is related to the ratio of the amount of light striking the filter and the amount of light that passes through the filter... and for fun we take the base 10 logarithm of that ratio. Thus by definition:

Optical Density=Log₁₀(incident light ÷ passed light)

For example, with a three step ND filter the amount of light striking the film or sensor is 1/8 the amount of the source light (1/2, 1/4, 1/8...) and Log₁₀(1 ÷ ¹/₈)=0.9. A three step ND filter has an optical density of 0.9 (there are no units associated with this value).

When using Lee brand filters the "Little Stopper" is a neutral density filter that reduces the light entering your lens by six stops and Lee calls that a ND 1.8. The "Big Stopper" is a ND 3.0 or ND 110 or ND1000. Side note: some ND filters are reported to have a slight color cast so choose with consideration.

Thanks for reading,
Casey

Comments: view entire thread

Or use your Noc wide open at noon 😉 [nt]

By: 5980 : May 5th, 2018-17:56

\(ツ)/ ... I have been testing the ND 3.0

By: cshimokita : May 5th, 2018-19:09

Should have some results in a couple of days. I was reading last night about how many photographers like the morning or evening light, but a "select few" love to shoot at high noon ; ). It was in her book "Annie Leibovitz at Work"... normally I give a mis...