Round, Continuously Variable, Neutral Density Filter Wheel for Cage Systems
- Circular, Continuously Variable, Reflective Neutral Density Filter
- Optical Density Range: 0 - 2.0 or 0 - 4.0
- Ø50 mm Filter Wheel
- Designed for Use with SM1 Lens Tubes and 30 mm Cage Systems
Thorlabs' Round, Continuously Variable, Metallic (i.e., reflective) Neutral Density Filters for Cage Systems are specifically designed for compatibility with our SM1 (1.035"-40) Lens Tubes and 30 mm Cage Systems. 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 to 2.0 or 0 to 4.0. For the variation of optical density with angle, please refer to the Specs tab.
The circular filter wheel measures 50 mm in diameter and is attached to a rotating lever arm so that it can be moved out of the beam path. The rotating axle comes with angular graduations that improve repeatability. In addition, an 8-32 (M4) tapped hole is provided in the base to allow for mounting to Ø1/2" TR Series Posts and accessories. The plates on either side of the filter wheel contain an internally threaded SM1 port and have four through holes that allow mounting to our ER cage system assembly rods.
The optical density, OD, is defined by the 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.
|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)||±1o|
|Spectral Range||240 - 1200 nm|
|Coating||Front: Inconel (NiCrFe)|
|Irregularity (per cm2)||<λ|
|Surface Quality||60-40 Scratch-Dig|
|Optical Density Tolerance||±5% (At Both Extremes)|
|Chamfer||0.2 mm x 0.2 mm|
| Round Continuously Variable Metallic ND Filters (Unmounted Dimensions)|
|Item #||Optical Density (OD)||A||B||C||D||E||F|
|NDM2||0 - 2.0||50 mm||7.5 mm||8 mm||48 mm||270o||2 mm|
|NDM4||0 - 4.0||50 mm||7.5 mm||8 mm||48 mm||270o||2 mm|
Optical Density as a Function of Angle
The optical density is a linear function of the angle:
OD = mθ
where OD is the optical density and θ is the angle in degrees. The value of m depends upon the optical density range of the particular ND filter:
- For filters with an OD range of 0 - 2.0, m = 0.00741.
- For filters with an OD range of 0 - 4.0, m = 0.0148.
This formula assumes 0° at the point where the coating begins and 270º at the end of the coating (i.e., the point of highest optical density).
An example of the standard cage
plate measurements determining
cage system compatibility.
Cage System Overview
The Cage Assembly System provides a convenient way to construct large optomechanical systems with an established line of precision-machined building blocks designed for high flexibility and accurate alignment.
16 mm, 30 mm, and 60 mm Cage System Standards
Thorlabs offers three standards defined by the center-to-center spacing of the cage assembly rods (see image to right). The 16 mm cage, 30 mm cage, and 60 mm cage standards are designed to accomodate Ø1/2", Ø1", and Ø2" optics, respectively. Specialized cage plates that allow smaller optics to be directly inserted into our larger cage systems are also available. All locking setscrews used in these cage plates are standard 4-40 setscrews, which use a 0.05" hex key.
The flexibility of our Cage Assembly System stems from well-defined mounting and thread standards designed to directly interface with a wide range of specialized products. The three most prevalent thread standards are our SM05 Series (0.535"-40 thread), SM1 Series (1.035"-40 thread), and SM2 Series (2.035"-40 thread), all of which were defined to house the industry's most common optic sizes. Essential building blocks, such as our popular lens tubes, directly interface to these standards.
|Standard Cage System Measurements|
|Cage System||16 mm||30 mm||60 mm|
|Rod to Rod Spacing||16 mm (0.63")||30 mm (1.18")||60 mm (2.36")|
|Total Length||25 mm (0.98")||41 mm (1.60")||71.1 mm (2.8")|
|Cage Rods||16 mm||These rods are used to connect cage plates, optic mounts, and other components in the cage system. The SR Series Cage Rods are compatible with our 16 mm cage systems, while the 30 mm and 60 mm cage systems use ER Series Cage Rods.|
|Cage Plates||16 mm||These serve as the basic building blocks for a cage system. They may have SM-threaded central bores, smooth bores sized for industry standard optics or to accommodate the outer profile of our SM Series Lens Tubes, or specialized bores for other components such as our FiberPorts.|
|Optic Mounts||16 mm||Thorlabs offers fixed, kinematic, rotation, and translation mounts specifically designed for our Cage Systems.|
|Cage Cubes||16 mm||These cubes are useful for housing larger optical components, such as prisms or mirrors, or optics that need to sit at an angle to the beam path, such as beamsplitters. Our cage cubes are available empty or with pre-mounted optics.|
|Post and Breadboard Mounts and Adapters||Mounting options for cage systems can be found on our Cage System Construction pages. Cage Systems can be mounted either parallel or perpendicular to the table surface.|
|Size Adapters||Cage System Size Adapters can be used to integrate components from different cage system and threading standards.|
|Specialized Components||Thorlabs also produces specialized cage components, such as Filter Wheels, a HeNe Laser Mount, and a FiberPort Cage Plate Adapter, allowing a wide range of our products to be integrated into cage-mounted optical systems. Explore our Cage Systems Visual Navigation Guide to see the full range of Thorlabs' cage components.|