ND3.0 neutral density filter 1.25"

1.  Neutral Density Filters Introduction

Neutral Density (ND) filters are designed to reduce transmission evenly acorss a portion of a specific spectrum. ND filters are typically defined by their Optical Density (OD) which describes the amount of energy blocked by the filter. A high optical density value indicates very low transmission, and low optical density indicates high transmission (Equations 1-2). ND filters can be stacked to achieve a customs optical density. To calculate the final system OD, simply add the OD of each filter together.

Types of Neutral Density Filters

There are two types of ND filters: reflective and absorptive.

Reflective ND filters consist of thin film optical coating, typically metallic, that have been applied to a galls substrate. The coating can be optimized for specific wavelength ranges such as UV-VIS or NIR. Thin film coaitng primarily reflects light back toward the source. Special care should be taken to ensure the reflected light does not interfere with the system setup.

Absorptive ND filters utlize a glass substrate to absorb light by a specific percentage.

WARNING: The filters of Optolong are not designed for sun observation. DO NOT LOOK AT THE SUN WITH OPTOLONG FILTER. You would be BLIND if you fail to observe the warning.

2. ND3.0 Filter Characteristic
Sbustrate: optical galss
Thickness: 1.85mm
T=0.1%
Surface quality: 60/40
Transmitted Wavefront RMS: λ/4
 Parallelism: 30s

3. Coating Technology

·Multi-layers anti-reflection coating

·Non-cementing optical substrate coating

·Optolong filter adopts precision coating based on Ion-assisted deposition coating technology for durability and resistance to scratching, as well as stability on CWL(central wavelength) no deviation affected by temperature change.

·Planetary rotation system offers precision and homogeneity of coatings ensuring high value on transmission of pass-band and Optical density of off-band.