Round, Step-Variable, Metallic Neutral Density Filters
Thorlabs' circular, step neutral density filters are available in two different sizes with 8 or 10 steps in optical density.
If you wish to mount one of these filters onto a TR series post, that can be accomplished using the NDC-PM Post Mount Assembly shown below.
The mounted versions of our step neutral density filters come with angular graduations and on 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.
The post, post holder, and base shown to the left are not included.
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" TR Series 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 use, unscrew the thumbscrew on the side with three washers, remove two of the washers, insert the filter wheel, place the two washers back on the thumbscrew threading, and re-thread the thumbscrew (see photo to the right). Two of the included washers are used to hold the wheel on the axle while the other two (one on each side) are used to ensure smooth turning motion. The two thumbscrews thread into a special 0.75" long ER rod whose position can be translated using the included 0.050" allen key. If a longer distance is needed between the post and the filter wheel, you could simply swap out the included 0.75" long ER rod for any other standard length.