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Neutral Density Filter

Name: Neutral Density Filter
Brand: ECOPTIK INDUSTRIAL PTE.LTD.

This is a very unique and practical optical component, whose core function is to uniformly reduce the intensity of all wavelengths (colors) of light without changing the spectral composition and color balance of the light source.

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Features of Neutral Density Filter

ECOPTIK makes fixed OD value neutral density filter by depositing Inconel film on a clear cubstrate. The advantage of the optical density filter is in the broader band and lower ripple than that of absorptive density filter. The coated wavelengthcan be extended to 200nm to 1100nm or more. The disadvantage is that there is some reflective light on the optical filter glass. The OD value can vary from 0.1 to 0.5. The OD value is controlled by coating inconel thin film thickness. Regular thickn thickness of the NDF is 1.1mm or 0.55mm.
This kind of optical density filters can be used for video, waterfalls, ophthalmology and landscape photography.

Specification of Neutral Density Filter

Material	BK7
Diameter tolerance	+0.0/-0.1mm
Thickness tolerance	±0.1mm
Parallelism	<3 arc min
Flatness	λ~λ/10
Clear aperture	>90%
Density tolerance	±2%
Part No. Wanvelength Range(nm) Optical Density (OD)@550nm	ND01 400-1100 0.1 ND02 400-1100 0.2 ND03 400-1100 0.3 ND04 400-1100 0.4 ND05 400-1100 0.5 ND06 400-1100 0.6 ND07 400-1100 0.7 ND08 400-1100 0.8 ND09 400-1100 0.9 ND10 400-1100 1 ND20 400-1100 2 ND30 400-1100 3 ND40 400-1100 4 ND50 400-1100 5

Neutral Density Filter Types

1. Absorption type ND filter

Working principle: Made of glass or optical plastic containing uniformly suspended carbon particles or metal particles. These particles uniformly reduce light intensity by absorbing light energy and converting it into thermal energy.

Features:

Advantages: Low cost, insensitive to incident angle, and less prone to stray light.

Disadvantages: Under high-power laser, it may rupture or produce thermal lens effect due to heat absorption, and its neutrality may not be as good as that of reflective type.

2. Reflective ND filter

Working principle: Coat a metal film with neutral reflective properties (such as chromium, nickel chromium alloy, inconel) on a glass substrate. Reduce light by reflecting (rather than absorbing) a portion of the light.

Features:

Advantages: It usually has better neutrality, high temperature resistance, and high power.

Disadvantages: High cost, reflected light may form ghosting or stray light, affecting system performance.

3. Reflection/absorption hybrid type

Combining the advantages of both, it is commonly used in high-end photography ND mirrors to minimize ghosting caused by reflection while ensuring neutrality.

4. Variable ND filter

Working principle: Composed of two linear polarizing plates. When a polarizing film is rotated, the angle between its polarization direction and the other film changes, thereby continuously changing the transmittance.

Features:

Advantages: One filter covers multiple OD values, which is very convenient.

Disadvantage: It is not truly "neutral" and is sensitive to polarized light, which may result in uneven sky color or "cross shaped" dark corners. The imaging quality is usually inferior to fixed ND mirrors.