Conic frusta1


Conic frusta 1

Heat forming tool Learned from Dr. E. Kelley at NIST Boulder in 2008 winter

Configuration factor calculation

Specular reflection cut design and desired field of view

Shape: apex angle 90 degrees cone, largest dia 75mm,
apertures :25/30mm material:black PVC (0.5t)

material:black PVC (0.5t)

  • Minimum reflecting surface area parallel to apertures
  • Visual filed restriction
  • Stray light elimination: 95%
  • Eliminate specularly reflected light from scattered light

Conic frusta1 is a pair of black PVC cones made by heat forming, glued afterwards.

The conic frusta is used for visual field restriction of the camera, where it is supposed that the light is incident substantially normal to the apertures. Because of its minimum reflecting surface area parallel to the apertures, minimum back reflection to the object and to the imager are expected.

Stray light incident on an aperture on the cones at oblique angle is subject to multiple reflection on the inner wall of the cones and can not come out from another aperture. Therefore, stray light elimination is approximated by aperture to aperture “configuration factor” shown in the right.

When we put a reflector after the exit aperture, we can rotate it somehow so that its specular reflection can not come out from the entrance aperture. This fact is applied in our speckle contrast measurement, where specular reflection on the screen must be totally avoided from the scattered light which interferes with each other to generate speckle.

Oxide Corporation

Speckle contrast Measurement System