These variable neutral density filters allow convenient adjustment of beam attenuation by simply rotating the filter. Optical density varies linearly with rotation angle across a 270° range from 0 up to the chosen maximum of OD1, OD2, or OD4. An arbitrary transmitted beam power may then be obtained easily using the angular markings to rotating the variable ND filter to the specific corresponding angle. Due to this linearity in density, the rotation may even be motorized to produce a precise logarithmic sweep in the transmitted beam power.

Fused silica substrate for these ND filters allows the transparency from 250-2500 nm range.

These filters consist of a thin metallic coating of variable thickness. Because attenuation is primarily caused by reflection with only a small amount of absorption, these filters may optionally be used as variable beamsplitters.

To prevent unwanted interference from etalon effects, filters should be angled slightly with respect to the incident beam. To minimize back reflections, the filter should be oriented with the coated metallic surface facing the incident beam. Any light reflected from the uncoated second surface will pass through the metallic coating first, which will greatly attenuate unwanted back reflections.

We offer a variety of rotary mounts for the variable neutral density filter. Please check out the accessories section below for recommendations. Shown is model compact circular variable ND filter mount.