Roger Ceragioli 's Refractor Construction Page

How to grind and polish a refractor lens and have it work well.

How to really make a decent Refractor
Written by several individuals including Roger
Introduction Introduction to the Article.
Preliminary Notes Basics of what a refractor is.
Planing on the Design The Fraunhofer design and some others are mentioned.
Buying the Glass How to buy the Glass and some places to buy it from.
Starting the Grinding Initial things to do for the grinding.
Figuring out what you want What Focal Length and type lens do you want to build.
Grinding start Initial hogging of the glass and making grinding tools.
Correcting for center and wedge What Focal Length and type lens do you want to build.
Polishing the Lens Polishing out the lenses and notes on milling rouge.
Figuring the Lens Figuring and initial testing of the lens.
Color Error Correction Working on the Color Correction and Spherochomatism.
Mounting Mounting the Lenses and cell notes.
Finishing the Testing Final alignment of the Lenses for Color and Astigmatism.
Appendix 1 Alternative designs for a refractor.
Appendix 2 Making and using testplates.
Appendix 3 Using undocumented glasses.



Introduction:
After making one or two paraboloidal mirrors for Newtonian telescopes, many amateur telescope makers turn their thoughts toward more advanced projects. Often they are attracted to making a refractor lens, but lack the information needed to do the job. Refractors, both achromatic and apochromatic, can provide stunning views of the moon, planets, and double stars, often exceeding even good Newtonians in the amount and sharpness of detail they will show. This webpage is designed to give advancing ATMs a guide to making their own refractor lenses.

I will assume that you have made mirrors before, and thus won't describe the basic processes of grinding and polishing glass, or testing an optical figure by means of a knife edge or Ronchi tester. Many books exist which detail these processes [my personal favorite is Jean Texereau's "How to Make a Telescope" (Willmann-Bell, 1984)]. Nor will I describe how to make an apochromatic lens, because the glasses for such a lens are quite expensive and the lens curves are a bit more difficult to make well than those of an achromatic lens. People who complete several successful achromats will be well prepared to tackle these more difficult lenses on their own. Instead, I will concentrate on the making of achromats because this type of color-corrected lens is not too costly nor difficult for a dedicated ATM, and can give superb results. The guidance given here will also help you to fabricate other transmission type optics such as the corrector lenses for Maksutov and Houghton systems.

Please note that when grit sizes are mentioned, they are generally not all that rigid in size as you may use 25 micron grit in place of 20 micron if that's what you have. If you are used to using 5 micron grit or even smaller, you may proceed to those sizes, remembering that refractor glass is softer than Pyrex so you will be cutting the glass faster than what Pyrex cuts and wets will be shorter.

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