Filter Cassette System

When research-grade filters get fairly large, a filter slide is often a better choice than a filter wheel.  DFM offers a Filter Cassette Changer System utilizing an 8-position filter cassette.  These filters, when integrated with 3 or more telescopes on the same site, allows for seeing in color as well as full-frame Space Object Identification (SOI), and essential feature for Space Situational Awareness (SSA).

Each filter is mounted within its individual cell. The desired filter is selected and the body of the filter cell is placed into the loading dock. The push-pull rod is then used to push the filter into the camera focal area. The filter and its cell are magnetically latched into position. The magnet is located within the camera instrument housing.

The filter cells roll on wheels along "V" groove tracks from the outside of the OTA into position on the center line of the optical system. The "V" wheels are machined from Delrin (a relatively hard and low friction plastic). The tracks have matching "V" grooves and are made of black anodized aluminum.

To remove the filter, the push-pull rod is pulled overcoming the magnetic latch and then the filter and its cell are rolled out into the loading dock. The filter, its cell, and the push-pull rod is then removed from the loading dock as an assembly.

The filters fit into a recess in the cell and are retained by 2 elastomeric clamps. The elastomere is a short piece of silicon rubber tubing. There is a button head screw running through the hole in the tubing. When the screw is tightened, the rubber attempts to expand radially and extrudes out of its hole against the edge of the filter. We have used this technique on may filter wheels and filter slides to safely retain filters. 

  • 8-position filter cassette
  • The filters are 125-mm X 125-mm X 9-mm thick research-grade filters
  • Cells are thicker than the filters to protect the surfaces of the filters.
  • The filter and its cell are magnetically latched into position