Circular Variable Neutral Density (ND) Filters are continuously variable over 270° of the filter. These filters provide linear attenuation of incident light by rotating the filter. The filters are designed to be spectrally flat from 380 to 2000nm in H-K9L and 250-2500nm in Uv fusedsilica, they can provide excellent attenuation for spectrometers and other optical instruments.These filters have optical densities ranging from 0.04 to 4.0. The optical density increases linearly from the start ofthe coating. For more information, please refer to the specs tab below.
| Substrate Material：See details in the list | Surface Quality：60/40 |
| Outer Diameter tolerance：+0/-0.25mm | Surface flatness：1 wave/cm² @ 633nm |
| Inner Diameter tolerance：+0.25/-0.00mm | Optical Density Linearity：+/-5% |
| Thickness：2mm | Optical Density Tolerance：+/-5% |
| Thickness tolerance：±0.25mm | Spectral Range：See details in the list |
| Parallelism：≤ 3′ | |
