About adjusting Null corrector lens to correct distance

I have discussed a method of inserting a mechanical iris in front of the Null lens in order to easily adjust it to its correct position.

Originally published 15.2.2013 by Jani Achrén. You can read the rest in here (blog) and here (pdf).


Low-cost interferometric testing for conical surfaces

A two-slit interferometric wavefront error measuring technique combines high sensitivity and low-cost components.

Testing of conical surfaces for mirrors or lenses most often require interferometry and with it, expensive devices to detect wavefront aberrations.

A two-slit Interferometric wavefront error measuring technique, first deviced by Yrjö Väisälä of Tuorla Observatory, combines high sensitivity (much higher than with traditional Foucault or Ronchi tests) with few layout components most probably already in posession of ATM mirror manufacturers. The principles of this test have been developed into an interferometric Hartmann test.

Originally published 14.2.2013. You can read more about it here.