Thin Metal Films

Neutral Density Filters

Neutral Density or check filters have many applications but are generally used in the attenuation of energy covering the NUV-VIS-NIR band. Because the attenuation is achieved by a combination of absorption and reflection, the filter can be used as beamsplitters in some applications.

TMF manufactures a range of ND filters covering ND 0.1. to ND 3. and can be optimised at any wavelength from 350 to 1100nm.

The relationship between neutral density ND and transmission T is ND = log 1/T 

To achieve neutrality of attenuation with wavelength, nickel chrome alloy is used in their construction. This material is extremely durable when applied to quartz and glass, less so on plastic substrates.

ND Configurations

TMF offer three configurations:

Plate

The required density applied uniformly to the entire surface.

ND Range: 0.1 to 3
Wavelength: 400-1100 (Glass)
300-2000 (Quartz)
Tolerance on ND: +/- 5%
NEUTRAL DENSITY FILTERS - Plate

Zonal

This is a graded circular ‘spot’ being most dense at the centre and normally decaying to zero at the outside of the substrate. 
This is a very valuable filter in CCT cameras to increased the dynamic operating range.

ND Range: 0.5-3
NEUTRAL DENSITY FILTERS - Zonal

Step

ND Filters can be applied in discrete steps across the substrate
in both linear or radial manner.

Reflectivity: >95% 360-410nm
Transmission average 70% Visible
NEUTRAL DENSITY FILTERS - Step

Please call or email us to discuss any variations in standard coatings that you may require.

Download Specification in PDF format