These filters possess level spectral transmittance characteristics in the visible region and attenuate light by absorption with minimal reflection comparing with reflective ND filters. Typically, neutrality and density of absorptive filters are a function of the material and the thickness. They are useful in light control applications for measuring instruments and exposure control in imaging. Spectral variations occur as optical density increases. Optical Density exhibits an additive relationship; for example, stacking filters with OD values of 0.6 and 0.9 yields a resultant density of 1.5.
| Material：Neutral grey glass | Thickness：±0.5mm |
| Flatness：λ/4@633nm | Application Range：400~700nm |
| Parallelism：<1' | *OD Tolerance：±5% @633nm |
| Surface Quality：60/40 | Clear Aperture：>90% |
| Dimension Tolerance：+0.0/-0.2mm | *Optical Density(OD)：OD= -log(T/100) |
