/My Tester

My Tester

Some Ideas That Work for Me

My present tester is shown in the pictures here. It is the "rocker" type that uses a rocking motion of the carriage to cut the knife edge in and out of the focus area. It is probably not suitable for the caustic test. The linear slide is kinematically stable, and is based on that of a lathe tailstock.
Some of the features of my tester are:

Safety: the knife edge is protected from damage by contact with your cornea.
The convertible light tower: you can change from pinhole to slitless to ronchi quickly and easily.
Special attention to the need for uniform illumination of the pinhole
The inverted vee track for the carriage, same scheme as a lathe tailstock.
Lapped hardware store threaded rod provides very accurate positioning and precise motion for the carriage. The screw provides enough travel to test a 200" f/3.33 mirror.
A large knob with fifty divisions. How to make a GREAT knob for a tester or other precision machine
Use of rubber bands to eliminate all backlash.

Slitless Test

Ronchi Test. The rulings in the grating are actually vertical.

Tester Internals, showing undercarriage and ample rubber bands to avoid backlash. Interference fringes from a part of very large reference flat are shown in the background.The flat was accidentally smashed by my wife.

Future Goals for My Next Tester

Ability to carry a null lens in the light cone.
Ability to separate the light source from the knife edge to provide null testing of elliptical mirrors, tilted mirrors, astigmatic mirrors, and near-null testing of deeper hyperbolic mirrors.
Beam splitter to provide precise concentricity of outgoing and incoming light.

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