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Knight Optical(UK) Ltd - - +44 (0)1622 859444

Absorptive glass neutral density filters

What are you looking for in Stock?

Glass Neutral Density filters 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. They also attenuate by absorption and so care must be taken to avoid overheating. Attenuation is achieved by polishing glass to the correct thickness.

Knight Optical offers stock absorptive ND filters in 12.5mm and 25mm diameters, and 50x50mm squares manufactured from high quality glass. Each filter is available with blocking between 0.1 and 4.0 OD and are available to purchase direct from this page.

In addition to our stock absorptive glass ND filters, Knight Optical also offers an extensive custom optic service thanks to our many years of experience in the industry. We are able to supply ND filters cut to sizes and shapes to fit individual application and mount filters where applicable. For more information on our custom glass ND filters, or for more information on our entire filter range, contact our technical sales team.


Material:   Colour Glass
Optical density :  ± 12.5% (@546nm)
Diameter:  +0.0 / -0.2 mm
Length / width:  ± 0.2 mm
Thickness:  Varies between batches to control the OD
Surface quality:  <60-40 scratch/dig
Flatness:  <2.5λ over 90% test area
Parallelism:  <3 arcmin


  • Mounting of diameters and squares.
  • Antireflective coatings can be applied to one or both faces for improved transmission.
  • Cutting down or edged to special shapes and sizes at short notice..
  • Available in sets, supplied in a wooden storage box for research and laboratory use.

Stock Optics

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Part No. Density @ 546nmTrans (%) @ 546nmThick
Equivilent materialMaterial Price
FNG0113 Download 0.1790.612.5NG11 £11.90
FNG0125 Download 0.1790.625NG11 £18.65
FNG0213 Download 0.2631.412.5NG11 £11.90
FNG0225 Download 0.2631.425NG11 £18.65
FNG0250 Download 0.2631.45050NG11 £38.25
FNG0313 Download 0.3502.312.5NG11 £11.90
FNG0325 Download 0.3502.325NG11 £18.65
FNG0350 Download 0.3502.35050NG11 £38.25
FNG0413 Download 0.4403.212.5NG11 £11.90
FNG0425 Download 0.4403.225NG11 £18.65
FNG0450 Download 0.4403.25050NG11 £38.25
FNG0513 Download 0.5324.112.5NG11 £11.90
FNG0525 Download 0.5324.125NG11 £18.65
FNG0550 Download 0.5322.35050NG11 £38.25
FNG0613 Download 0.6252.312.5NG5 £11.90
FNG0625 Download 0.6252.325NG5 £18.65
FNG0650 Download 0.6252.35050NG5 £38.25
FNG0813 Download 0.8163.112.5NG5 £11.90
FNG0825 Download 0.8163.125NG5 £18.65
FNG0850 Download 0.8163.15050NG5 £38.25
FNG1013 Download 1103.912.5NG5 £11.90
FNG1025 Download 1103.925NG5 £18.65
FNG1050 Download 1103.95050NG5 £38.25
FNG1513 Download £11.90
FNG1525 Download £18.65
FNG1550 Download £38.25
FNG2013 Download 213.812.5NG4 £11.90
FNG2025 Download 213.825NG4 £18.65
FNG2050 Download 213.85050NG4 £38.25
FNG2513 Download 2.50.322.412.5NG3 £11.90
FNG2525 Download 2.50.322.425NG3 £18.65
FNG2550 Download 2.50.322.45050NG3 £38.25
FNG3013 Download 30.12.912.5NG3 £11.90
FNG3025 Download 30.12.925NG3 £18.65
FNG3050 Download 30.12.45050NG3 £38.25
FNG4013 Download 40.013.912.5NG3 £11.90
FNG4025 Download 40.013.925NG3 £18.65
FNG4050 Download 40.013.95050NG3 £38.25
FNG2552 0.352125X £13.20
FNG2584 0.07684%@565nmX25X £13.20
FNG2588 0.05488.28%@565nm1.125X £13.20
FNG2572 0.1372.4-74.4%@565nm0.9525X £13.20
FNG2571 0.1571%@565nm1.225X £13.20
FNP2799 1.1x227.2 £18.65
FNG3020 Download £38.25
FNG2554 0.2654.6-56.6%@565nm2.1526X £13.20

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Get in touch

Our Multi-Lingual Sales Team are here to help with your requirments:

UK +44 (0)1622 859444
UK +44 (0)1622 850614
UK +44 (0)1622 851078
+1 401 583 7846

International Shipping

We are able to ship to most countries at good rates, please click here for more info.

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