Amateur Telescope Making Main Page

Amateur Telescope Making Main Page

Russell Porter
Grinding a Mirror

“For it is true that astronomy, from a popular standpoint, is handicapped by the inability of the average workman to
own an expensive astronomical telescope. It is also true that if an amateur starts out to build a telescope just for
fun he will find, before his labors are over, that he has become seriously interested in the wonderful mechanism of
our universe. And finally there is understandably the stimulus of being able to unlock the mysteries of the
heavens by a tool fashioned by one’s own hand.”

Russell W. Porter
Founder of Stellafane, March 1923

Introduction

A lot has changed since Russell Porter wrote those
words – today the “average workman” can afford to buy an already
made telescope and Dobsonian mountings are very popular.  Much
is also unchanged – mirror grinding techniques are very similar to
those written up by Porter and Ingalls in the 20´s and 30´s. Many
amateur astronomers still choose to fabricate their own instruments,
for the pride of accomplishment, the gaining of knowledge and the
insurance of quality. Telescope making is at the heart of the
Springfield Telescope Makers – after all it is two thirds of our
club’s name – and on these pages we hope to show you that you too
can make your own telescope – and it can be an excellent performer!

A note on ATM techniques: There are almost as many ways to
make mirrors and telescopes as there are telescope makers. On these
pages we present one or more ways that have worked for us, but that
doesn’t mean there aren’t many other valid approaches. In fact, many
of us enjoy ATMing because we can experiment with different
techniques and sometimes find better ways of making or building a
telescope. And even if our new technique isn’t better, we usually
learn something valuable in the process. On these pages, however, we
have tried to stick with simple and proven techniques that are most
appropriate for novice mirror and telescope makers, and are
generally what we teach beginners at the
Stellafane Mirror Class.

Amateur Telescope
Making Table of Contents

General Information

Selecting a
Telescope
Provides basic information about telescope for beginners, and
briefly discusses important factors that should be considered in
Selecting a First Telescope.

Are You Ready for
a Telescope?
Objective
Size is Important
Types of
Telescopes
Types of Mounts
Portability
Make or Buy?
Why Newtonian
Reflectors on Dobsonian Mounts are a Good First Scope
Selecting Mirror
Size and Focal Length

Mirror Making Myths
& Information for the Curious
There are a lot of misconceptions about making a mirror –
read this even if you don’t plan to make a mirror, but just want
to know how it is done – with your bare hands and a few
simple tools, you can grind and figure a fine mirror with a
surface accurate to a few millionths of an inch!

Telescope
Formulas and Design Comparator
This page has formulas for many telescope and mirror
parameters. It will calculate parameters for two different
telescope designs and compare the results for you. It provides
data to help in selecting a telescope, and also provides
information necessary for mirror making and testing.

Telescope Mirror Making

Overview
of Mirror Making

Pyrex Mirror Blanks

Materials and Tools

The Mirror Blank

The Tools: Grinding & Polishing

Grits & Pitch

Grinding Stand: Barrel, Stand or Turntable

Build an ASGH Wooden Barrel

Storage Containers: Mirror, Pitch Lap & Grit

Miscellaneous

Grinding

Making a
Tile Tool

Making a
Plaster Disk
Tile Tool
Problems – What to do

Selecting a
Surface to Grind

Beveling
the Edges

Rough
Grinding

What is a Wet?

Fine Grinding

When to
Switch Grits
About Scratches
The Pencil
Test – checking for “Good Contact”

Polishing in the McGregor Observatory

Measuring
Sagitta

Polishing

Pouring a
Pitch Lap

Making a Plaster
Disk

Removing an Old Lap

Lap Maintenance

Hot & Cold Pressing

Trimming Channels & Edges

A
Heated Electric Channel Cutter

Brushing a Glazed Lap

A Pitch Hardness Tester

How to Store Your Lap
Using Old
Pitch

Polishing

When is my
Mirror Polished Out?
Temperature
& Humidity Considerations
About
Turned Down Edge
About
Polishing Pads

Figuring

Introduction to Figuring

A Change of Pace – Figuring first to a
Sphere and then to a Parabola

Mirror
Coatings

Aluminizing, Silvering & Enhanced
Coatings

Mirror Making References & Calculators

Telescope Formulas and Design Comparator

Sagitta to Focal Length Calculator

Guide to
Grit, Polish & Pitch

Grit: Material,
Sizes

Grit Size Table

Polishing Compounds

How to Mix Cerium Oxide

Pitch
How much
Grit, Pitch & Polishing Compound will be Needed?

Safe Handling & Storage

Guide to Strokes
(includes many short videos)
How to Clean a Coated Mirror

Optical Testing

Cody Tests his Mirror

Testing
Overview
Why we advocate using both Ronchi &
Foucault Tests.

Video that reviews all
common amateur test techniques.

Basic Testing Knowledge

Reading Ronchigrams
Selecting a
Ronchi Grating

Understanding Foucault
Testing
Reading Shadowgrams
Measuring
Parabolas

Mirror
Quality
How good is Good Enough?

Polish Quality

Surface Quality

Figure Quality

Practical Testing

Setting up your Tester
Testing for a Sphere with a Good Edge
Testing for a Parabola

Auto-Collimation Testing
Telescope System Tests

The Star Test
The Ronchi Test

Building
Mirror Test Equipment

The Stellafane Tester

Complete plans for all the test equipment you need to
accurately test and figure your mirror.

Build a Foucault / Ronchi / Knife-Edge
Tester

Page 1: Base & Stage
Page 2: Head & Setup
Aids
Page 3: Electrical
Page 4: After Thoughts
Page 5: Parts
Reference

Build
an Adjustable Mirror Test Stand

Make a Couder
Mask and Everest Pin Stick

Calculate
Mirror Zones
to make a Mask or Pin Stick for your mirror.

Print a Ronchi Screen
on your Inkjet or Laser Printer

Foucault Data
Reduction Software

Our Dobsonian Telescope

Build a Dobsonian
Telescope

Plans for building a Newtonian Optical Tube and a Dobsonian

Mount for 4 to 12 inch telescopes.

Complete step-by-step instructions for both the optical tube

and Dobsonian mount.

ATM Resources & References

Books &
Periodicals
Information about the publications we use to develop or check
the information on these pages.

Internet Resources on our
Links Page

ATM Web
Pages
Hundreds of links to all aspects of telescope making on
the internet.

ATM Material Suppliers
US suppliers of Mirror Blanks, Grinding & Polishing
Supplies, and Telescope Making Supplies.

Astronomy Clubs
Many can offer help with your project.

Astronomy Conventions & Star Parties
A good place to look at various telescopes and chat with
their owners.

Mirror Making
Courses & Workshops
A world-wide list of Mirror Making Courses we know about,
part of our Mirror Class section.