Menu Contents

NeutralDensityFilter

ND.png

[ND filter]

An ND filter has a constant transmittance over a specific wavelength range. Optical elements, especially those that correspond to the visible wavelength range are transmissive The color tone of the light does not change. It is used widely. Its optical performance is expressed as OD (Optical Density). Calculated from the transmittance T using the following formula.

OD = log10 (1 / T)  * T = Transmittance (≦ 1)

Example) OD = log10 (1 / 0.05) ≒ 1.3 when transmittance T = 0.05 (5%)

ND filters may be used in combination of multiple sheets, The total OD is the sum of the OD of each filter.

Reflective and transmissive

ND filters are roughly classified into two types: “reflective ND filters” that reflect light that does not pass through and “absorptive ND filters” that absorb light.
A reflective multilayer ND filter uses a dielectric multilayer film or a metal film, but unwanted light is reflected, which causes the problem of stray light (ghost).
May occur. On the other hand, the absorption type ND filter absorbs almost no unnecessary light, so the reflection on the film surface is extremely low and stray light
The biggest feature is that it is less likely to cause problems. However, it is an extremely complex film design that combines a dielectric film and a metal film.

Features of our absorption type ND filter

General absorption ND filters tend to change their transmission characteristics gradually because the composition of the constituent films is likely to change depending on the environment. Bugs are often a problem. As a result of our verification of commercially available ND filters, the characteristics fluctuate significantly depending on the environment. It was confirmed that We have established a method to solve this problem, and there is almost no change in characteristics even in a harsh environment of 200 ° C × 200H. We have achieved both environmental resistance and optical performance at a high level.

Absorption-type ND filter Example of optical characteristics

ND Filter