Neutral density filters
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Neutral density filters attenuate light by a constant amount that is, to first order, independent of the wavelength neutral density filters are designed to equally reduce the transmission over a specified spectrum, either by absorption or reflection. Knight Optical stock several ranges for your specific application.
Gelatin neutral density filters: Gelatin ND filters are the cheapest but tend to have more fluctuation with wavelength and a narrower wavelength range than glass ND filters and metallic types. Gelatine neutral density filters work by absorption so care must be taken to avoid overheating which can lead to damage to the filter. Gelatine ND filters can also be cut easily to bespoke custom sizes in your own laboratory which can be extremely useful.
Absorption neutral density filters: Glass neutral density filters are the most common ND filter and attenuate light by absorption just like the gelatine neutral density filters. Glass ND Filters are more robust and tend to have more uniform absorption characteristics. As schott glass ND filters attenuate by absorption care must be taken to avoid overheating. Attenuation is achieved by polishing standard schott NG glasses to a given thickness.
Metallic neutral density filters: Metallic neutral density filters comprise a thin metallic layer on a borosilicate or UV grade fused silica polished windows. Metallic ND filters attenuate the light by reflection and thus avoid the possible heating issues with glass and gelatine neutral density filter types. However care must be taken to ensure the reflected light does not cause problems. Our stock range of visible/NIR range of metallic neutral density filters are coated on low-expansion borosilicate glass substrates and cover the range from 350-2500nm. Our UV range of metallic neutral density filters are coated on UV grade fused silica and therefore cover the useful UV region down to 170nm. All metallic ND filters are supplied with a copy of the spectral transmittance scan taken on a filter at the time of the production coating. We stock uncoated borosilicate and UV fused silica substrates so custom metallic filters can be supplied to your specific request, please enquire.
Individual filters and sets can be supplied to the customer’s specification.
Knight Optical supply high quality neutral density filters from stock or made to our exact specification. Every component is individually tested on our Agilent Cary 5000 spectrometers fitted with a UMA device for testing transmission and reflection at any given angle. Our Agilent 660 FTIR spectrometer is used for coatings between 3.5µm and 45µm. All tested by our highly skilled technicians in our state of art metrology lab to ensure all components meet our high quality standards. We can provide transmission and reflection curves at given wavelengths from 175nm up to 3200nm in TXT or CSV format, or other formatted options.
- Gelatine neutral density filters
- Absorptive glass neutral density filters
- Mounted absorptive glass neutral density filters
- Metallic neutral density filters
- Mounted metallic neutral density filters
- Neutral density filter sets