Variable ND Selection Guide
Image
ND Filter Type	Round Step	Round Continuous	Cage Compatible	Rectangular Step	Rectangular Continuous

Features

Circular, Step Variable, Reflective Neutral Density Filter
Optical Density Range: 0.04 - 1.0, 0.04 - 3.0, or 0.04-4.0
8 or 10 Steps in Optical Density
Ø50 mm and Ø100 mm Sizes
Transmissive in the 240 - 1200 nm Wavelength Range
Mounted and Unmounted Versions

Thorlabs' Round, Step-Variable, Reflective Neutral Density Filters provide 8 or 10 discrete optical density options, adjustable via rotation. They are composed of a UV fused silica glass substrate and a metallic Inconel coating through a full 270°, ensuring a flat spectral response from the ultraviolet to the mid-infrared. These filters have optical densities ranging from either 0.04 to 1.0, 0.04 to 3.0, or 0.04 to 4.0. Please refer to the Specs tab for more information.

The mounted versions of our step variable neutral density filters come with angular graduations and are mounted on a rotating axle. The mount has been carefully designed to minimize the effect on the clear aperture of the optic. Each mounted filter includes adapters for both 8-32 and M4 mounting holes, making the mounted filter compatible with Thorlabs' Ø1/2" TR Series Posts and accessories.

The optical density, OD, is defined by the equation:

Optical Density Equation

Hence, a higher OD corresponds to lower transmission and greater reflection of the incident light, while a lower OD corresponds to higher transmission and less reflection. For example, an OD = 2 filter will attenuate the transmitted beam to 1% of the incident intensity.

The Inconel coating on these filters is a very hard metallic alloy that is resistant to aging under normal conditions, but will oxidize at elevated temperatures. It is therefore recommended that the neutral density filters be used at temperatures below 100° C.

These filters are not intended to serve as laser safety equipment. For lab safety, Thorlabs offers an extensive line of safety and blackout products that significantly reduces exposure to stray or reflected light.

General Specifications
Substrate Material	UV Fused Silica
Diameter Tolerance (A & B)	Outer Diameter: +0.00/-0.25 mm Inner Diameter:+0.25/- 0.00 mm
Thickness Tolerance (C & D)	±0.25 mm
Coating Radial Angle (E)	±1^o
Spectral Range	240 - 1200 nm
Coating	Front: Inconel (NiCrFe) Back: Uncoated
Irregularity	<λ (per cm²)
Surface Quality	60-40 Scratch-Dig
Wedge	<3 arcmin
Optical Density Tolerance	±5% (At Both Extremes)
Chamfer	0.2 mm x 0.2 mm

Item Specifications

Unmounted, Round Step Metallic ND Filters
Item #	Optical Density*	A (mm)	B (mm)	C (mm)	D (mm)	E	F (mm)
NDC-50S-1	0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1.0	50	7.5	8	48	45^o	2
NDC-50S-3	0.04 (uncoated), 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0	50	7.5	8	48	45^o	2
NDC-100S-4	0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1.0, 2.0, 3.0, 4.0	100	7.5	8	98	36^o	2

Mounted, Round Step Metallic ND Filters
Item #	Optical Density*	Outer Diameter	A (mm)	B (mm)	C (mm)	D (mm)	E	F (mm)
NDC-50S-1M	0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1.0	2.5"	50	7.5	8	48	45^o	2
NDC-50S-3M	0.04 (uncoated), 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0	2.5"	50	7.5	8	48	45^o	2
NDC-100S-4M	0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 2.0, 3.0,4.0	4.5"	100	7.5	8	98	36^o	2

*The optical density is specified at 633 nm.

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Posted Comments:

Poster: apalmentieri

Posted Date: 2010-01-06 09:48:18.0

A response from Adam at Thorlabs to Motsnyi: I am sorry to inform you that we do not have accurate damage threshold information for the continuous and step ND filters for 350nm light. From past experience, these filters can typically handle an ~average power of 10kW/cm^2 and a peak power of ~1MW/cm^2 for 1064nm light.

Poster: motsnyi

Posted Date: 2010-01-06 08:02:42.0

What is damage trashhold at 350nm in terms of average and peak power?

Poster: TechnicalMarketing

Posted Date: 2007-12-27 12:16:53.0

Thank you for pointing out that the price box descriptions needed to be updated. This has been done.

Poster: acable

Posted Date: 2007-12-22 12:35:12.0

The price box descriptions need rewriting so the differences in each model show instead of all the characturistics that are the same. Perhaps just replacing Optical Density with OD would be enough.

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Round, Step-Variable, Metallic Neutral Density Filters

Features

Item Specifications