Autocollimators 3: Optical Design

In this episode of the Machine Tech Video Blog, I break down the optical system in an autocollimator piece-by-piece - from the light source to the eyepiece.

Here's the list:
Light Source (almost any will do; LED is preferable)
Target Reticle (crosshair markings are conventional)
Objective Lens (achromatic doublet with long focal length and wide aperture; irregularity precision 1/4 wave or better; anti-reflection coating is preferable)
Target Mirror (first surface mirror approximately same size as objective lens; flatness precision 1/10 wave or better)
Beamsplitter (50T/50R non-polarizing cube-type; precision flatness 1/4 wave or better; anti-reflection coating is preferable)
Scale Reticle (finer graduations = higher autocollimator resolution)
Eyepiece (should be well-corrected for aberration and must be able to focus on external reticle; higher magnification = higher autocollimator resolution)

I discuss the selection and arrangement of each one of these components, as well as many relevant concepts in optics which were not covered in the preceding two videos in the series. By the end of this video, you'll have all the knowledge you need to go out and build your own working autocollimator. In fact, that's exactly what I'm going to do in the next video. Stay tuned!

To purchase the optics kit I used in the video, do an eBay search for "Optical Concave Convex Lens Prism Set Physical Optical Kit Laboratory Equipment".

For further reading on this topic, check out "Metrology with Autocollimators" by K. J. Hume. It's a fantastic book, albeit hard to find.

Juicy jams by Sun Hop Fat - "Yègellé Tezeta": http://www.sunhopfat.com/


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