Round, Step-Variable, Metallic Neutral Density Filters
- Coated for Various Optical Density Step Sizes:
0.04 - 1.0, 0.04 - 3.0, and 0.04 - 4.0
- UV Fused Silica Substrate
- Spectral Range: 240 - 1200 nm
- Mounted and Unmounted Versions
Ø100 mm ND Filter
OD: 0.04 - 4.0
Ø50 mm ND Filter
OD: 0.04 - 1.0
Mounted Ø100 mm ND Filter
OD: 0.04 - 4.0
NDC-50S-3 Variable ND Filter
Mounted on Ø1/2" Post
Using an NDC-PM Mount
|Variable ND Selection Guide|
|Variable Absorptive ND Filter|
- Circular, Step Variable, Reflective Neutral Density Filter
- Optical Density (OD) 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.
Optical density (OD) indicates the attenuation factor provided by an optical filter, i.e. how much it reduces the optical power of an incident beam. OD is related to the transmission, T, by the equation
where T is a value between 0 and 1. Choosing an ND filter with a higher optical density will translate to lower transmission and greater reflection of the incident light. For higher transmission and less reflection, a lower optical density would be appropriate. As an example, if a filter with an OD of 2 results in a transmission value of 0.01, this means the filter attenuates the beam to 1% of the incident power.
Inconel is a metallic alloy that ensures flat spectral response from the UV to the near IR. Unprotected metal coatings like this should only be cleaned by blown air, never touched, as contact may cause scratching to the unprotected surface. Although these are reflective ND filters, the Inconel coating does absorb some of the incident light, which limits the use of these filters to low-power applications. Inconel is resistant to aging under normal conditions; however, it will oxidize at elevated temperatures. To prevent oxidation, Thorlabs recommends using these ND filters at temperatures below 100°C. To achieve the best performance light should be incident on the side with the Inconel coating.
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.
|Substrate Material||UV Fused Silicaa|
(A & B)
|Outer Diameter: +0.00/-0.25 mm
Inner Diameter:+0.25/- 0.00 mm
|Coating Radial Angle (E)||±1o|
|Spectral Range||240 - 1200 nm|
|Coating||Front: Inconel (NiCrFe)
|Irregularity||<λ (per cm2)|
|Surface Quality||60-40 Scratch-Dig|
|±5% (At Both Extremes)|
|Unmounted, Round Step Metallic ND Filters|
|Item #||Optical Densitya||A||B||C||D||E||F|
|NDC-50S-1||0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1.0||Ø50 mm||Ø7.5 mm||Ø8 mm||Ø48 mm||45°||2 mm|
|NDC-50S-3||0.04 (uncoated), 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0||Ø50 mm||Ø7.5 mm||Ø8 mm||Ø48 mm||45°||2 mm|
|NDC-100S-4||0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 2.0, 3.0, 4.0||Ø100 mm||Ø7.5 mm||Ø8 mm||Ø98 mm||36°||2 mm|
|Mounted, Round Step Metallic ND Filters|
|Item #||Optical Densitya||Mount
|Unmounted Optic Specifications|
|NDC-50S-1M||0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 1.0||63.5 mm||5.0 mm||Ø50 mm||Ø7.5 mm||Ø8 mm||Ø48 mm||45°||2 mm|
|NDC-50S-3M||0.04 (uncoated), 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0||63.5 mm||5.0 mm||Ø50 mm||Ø7.5 mm||Ø8 mm||Ø48 mm||45°||2 mm|
|NDC-100S-4M||0.04 (uncoated), 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 2.0, 3.0, 4.0||114.3 mm||5.1 mm||Ø100 mm||Ø7.5 mm||Ø8 mm||Ø98 mm||36°||2 mm|
Andreas Singldinger  (posted 2021-02-15 10:54:10.883)
It would be great, if there would be a motorized option of these ND filter wheels. Unfortunately, the FW102C and the ELL9K are both too large for our setup. Therefore I would definitely buy a remote controllable ND filter wheel of exactly this size. Maybe achievable with a small DC motor as a driving force and suspension point for the ND filter wheel.
YLohia  (posted 2021-02-16 11:57:05.0)
Hello, thank you for your feedback. We will consider adding such an item to our catalog in the future.
Jeroen Heuver  (posted 2019-09-02 06:08:29.137)
we are lookin for a optical density filter for a laser with the following specs: Wavelength 266 nm, 5 ns pulse width, beamdiameter 10 mm, 50 Hz pulsed laser of 5 watt (100 mJ/pulse). In future we need a filter for 50 Hz, 20 watt (400 mJ/pulse), 355 nm, 5 ns pulse width, diameter 10 mm. Will this optical density filter work for us? Will our laser create damage?
YLohia  (posted 2019-09-11 10:45:58.0)
Hello, thank you for contacting Thorlabs. Unfortunately, we do not have formal damage thresholds for these filters for your laser parameters. These filters are intended for low power use so damage is likely. I have reached out to you directly to discuss this.
felipe.hall  (posted 2016-08-15 13:21:13.543)
It would be great if there was a simple way to mount this on to the Compact Direct-Drive Rotation Mount (DDR05)for automated control. Perhaps some sort of adapter/mount? -Felipe Hall
apalmentieri  (posted 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.
motsnyi  (posted 2010-01-06 08:02:42.0)
What is damage trashhold at 350nm in terms of average and peak power?
TechnicalMarketing  (posted 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.
acable  (posted 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.
- Unmounted, Round, Step-Variable Neutral Density (ND) Filters
- OD Range
- 0.04 - 1.0 in 8 Steps (Item # NDC-50S-1)
- 0.04 - 3.0 in 8 Steps (Item # NDC-50S-3)
- 0.04 - 4.0 in 10 Steps (Item # NDC-100S-4)
- Filter Size
- Ø50 mm (8 Step Versions)
- Ø100 mm (10 Step Version)
- Thickness: 2.0 mm
Thorlabs offers unmounted, circular, step neutral density filters with angular graduations of increasing optical density. The filters have an optical density (OD) range of 0.04 - 1.0 (8 steps), 0.04 - 3.0 (8 steps), or 0.04 - 4.0 (10 steps) and are designed for use in the 240 - 1200 nm transmission range. Mounting of these filters onto a TR series post can be accomplished using the NDC-PM Post Mount Assembly shown below.
Click to Enlarge
NDC-100S-4M Neutral Density Filter Mounted on Ø1/2" Post
- Mounted, Round, Step-Variable Neutral Density (ND) Filters
- OD Range
- 0.04 - 1.0 in 8 Steps (Item # NDC-50S-1M)
- 0.04 - 3.0 in 8 Steps (Item # NDC-50S-3M)
- 0.04 - 4.0 in 10 Steps (Item # NDC-100S-4M)
- Filter Size
- Ø2.5" (8 Step Versions)
- Ø4.5" (10 Step Version)
Our unmounted step neutral density filters offered above are also available in mounted versions that have angular graduations and a rotating axle. The mount has been carefully designed to minimize the effect on the clear aperture of the optic and is an ideal, compact replacement for a filter wheel. Adapters for both 8-32 and M4 mounting holes are included with each filter, enabling compatibility with Thorlabs' Ø1/2" TR Series Posts.
Click to Enlarge
Step Filter Mounted on Post Using NDC-PM Assembly
The NDC-PM Post Mount Assembly allows you to mount any of our round, unmounted, step (or continuously variable) ND filters onto a rotating axle that can be threaded onto any Thorlabs Ø1/2" Post. The mount has a minimal effect on the clear aperture of the ND filter. Adapters for both 8-32 and M4 mounting holes are included with each mount.
To mount a filter, first tighten the setscrew on the side of the NDC-PM assembly using the included hex key to lock rotation. Using either a 5/64" or 2 mm hex driver, remove the silver screw, insert the filter between the two washers, and replace the wheel and screw assembly. Take care to replace the flat metal washer and spring washer in the original order (see video to the right), and tighten the bolt. The hex bolt threads into a 0.75" long Ø6 mm rod, the rotation of which may be locked using the included 0.050" hex key. If a longer distance is needed between the post and the filter wheel, the included 0.75" long rod can be swapped for a standard ER rod.