There are many ways to build a Dobsonian telescope, with many design decisions to be made. Our goal here is to guide you through building a basic Dobsonian that will function well, and our choices reflect that. Other plans may make other perfectly valid choices, or may have different design goals.
We break the project into two major pieces: theOTA and the Mount, and each piece is to some extent a separate project. The Newtonian OTA will be built in the classic Dobsonian-style cardboard concrete form tube, and while we plan to mate it to our Dobsonian Mount, it could certainly be attached to other types of mounts if desired by making a suitable set of tube rings or a tube cradle. Similarly, the Dobsonian mount we describe could be sized to fit an existing OTA, so if you have a telescope tube and want to mount it as a Dobsonian, you can just start at our mount project.
The Dobsonian Telescope Book Pdf
Optics: The mirror we will use in our sample scope was made at the Stellafane Mirror Class by the author, and we certainly encourage people to make their own telescope optics. However this project can use any suitable mirror you have, be it made by you, picked up on eBay or our at swap tables, or bought from a commercial supplier. Whatever source that works for you will work in this telescope.
Order of Construction: We have arranged the the steps in a logical progression below, and that is how we will proceed to built this telescope. There are dependencies: for instance you need to know the diameter and focal length of your mirror before you can size the tube, and you need to know the size and balance point of your tube before you can size your mount. To avoid rework and scrap, please proceed in the order we present the plans.
The Dobsonian Telescope, A Practical Manual for Building Large Aperture Telescopes tells how you can build a state-of-the-art Dobsonian telescope using readily available materials and supplies. Every step of construction is detailed in photographs and diagrams, and the underlying ideas are carefully explained. As a result of this three-year collaboration between authors David Kriege and Richard Berry, experienced and well-known telescope makers, you now have the opportunity to build a high-performance telescope from 14 inches to 40 inches aperture based on the thoroughly tested designs described in this book.
The Dobsonian telescope takes its name from the astronomer/philosopher John Dobson, who introduced the concept of inexpensive, large-aperture telescopes to astronomy. Amateur astronomers at the time were so amazed that a telescope built from simple, inexpensive materials performed so well that they could hardly believe their eyes. As home-built Dobsonians started showing up at star parties across the nation and people saw what Dobsonians could do, the word spread. In just a few years, the Dobsonian revolution swept the world.
Since those early telescopes, Dobsonians have improved dramatically. An entire generation of amateur telescope makers contributed their best insights and refinements to Dobson's original design. Today's Dobsonians are larger, lighter, and more precise than ever before. For example, it is possible to build a telescope of 20 inches aperture that is compact enough to transport in a hatchback automobile, yet takes only ten minutes to set up at a remote, dark-sky observing site.
Deep-sky observers especially appreciate Dobsonian telescopes. With the 20-inch (50 centimeter) aperture that the authors recommend for first-time Dobsonian builders, hundreds of globular clusters, thousands of nebulae, and tens of thousands of galaxies are visible through the eyepiece. Planetary observers have discovered that from good observing sites, Dobsonians deliver breathtaking performance on the moon and planets. For the casual stargazer, familiar objects like the Hercules Cluster, the Great Nebula in Orion, the Lagoon Nebula, and the galaxies of the Virgo Cluster are an entirely new experience.
Whether you have never observed before or whether you have been an amateur astronomer all your life, you will benefit from the hands-on familiarity and experience in amateur astronomy and telescope making that the authors bring to this book.
Chapter 1 Large Aperture Dobsonians 1.1 Why Dobsonians Are Newtonians 1.2 How Dobsonians Work 1.3 The History of the Dobsonian Telescope 1.3.1 John Dobson Invents the Dobsonian 1.3.2 The Dobsonian Revolution 1.3.4 The Second Dobsonian Revolution 1.4 The Dobsonian in Your Future Chapter 2 Planning Your Telescope 2.1 Non-Telescopic Telescope Considerations 2.2 Tough Telescopic Considerations 2.2.1 Telescope Aperture Considerations 2.2.2 Are You Obsessed? 2.3 How To Get Started Chapter 3 Engineering the Dobsonian 3.1 Engineering for Performance 3.2 Statics: How to Make a Stiff Telescope 3.2.1 Engineering Terms 3.2.2 The Moment of Inertia 3.2.3 Elastic Deformation 3.2.4 The Strength of Materials 3.2.5 Stiffness of a Truss Pole 3.2.5.1 Flexure in the Rocker Box 3.2.5.2 Flexure of a Telescope Mirror 3.2.5.3 Why Simple Scaling Doesn't Work 3.2.6 Dobsonian Dynamics: How Dobsonians Move 3.2.6.1 Balancing a Dobsonian 3.2.7 Friction in a Dobsonian 3.2.7.1 Friction Defined 3.2.7.2 Dobsonian Friction 3.2.7.3 Curing Stiction 3.3 Materials for Telescopes 3.3.1 Wood 3.3.1.1 Wood Is a Natural, Organic Composite 3.3.1.2 Wood Is Orthotropic 3.3.1.3 Selecting Wood 3.3.2 Aluminum 3.3.3 Teflon 3.3.4 Plastic Laminates 3.3.4.1 "Ebony Star" and "Stardust" Laminates 3.3.4.2 Glassboard 3.3.4.3 Put Car Wax on Laminates 3.4 Protective Coatings Chapter 4 Optics for Dobsonians 4.1 Basic Newtonian Optics 4.2 Choosing the Mirror 4.2.1 Choice 1: What Aperture? 4.2.2 Choice 2: What Focal Ratio? 4.2.3 Choice 3: Make or Buy? 4.2.4 Choice 4: What Glass? 4.2.5 Choice 5: Cut Sheet or Molded Blanks? 4.2.6 Choice 6: Fine or Precision Annealed? 4.2.7 Choice 7: How Thick? 4.2.8 Choice 8: Blanchard Ground? 4.2.9 Choice 9: What Coatings? 4.2.10 Choice 10: Optical Quality 4.3 Thinking About Eyepieces 4.4 Thinking About the Focuser 4.5 Sizing the Secondary Mirror 4.6 To Offset or Not to Offset? 4.7 Testing Telescope Optics 4.8 What To Do If You Don't Like a Mirror Chapter 5 The Primary Mirror Cell 5.1 The Flotation System and the Sling 5.1.1 Flotation in Theory 5.1.2 Flotation in Practice 5.2 Building the Flotation System 5.2.1 Flotation System Design 5.2.1.1 Material for Bars and Triangles 5.2.1.2 Flotation System Pads 5.2.1.3 Build the Cell Subassemblies 5.3 The Tailgate 5.3.1 Evolution of the Tailgate 5.3.2 The Open-Frame Tailgate 5.3.3 Tailgate Layouts 5.3.4 Cutting Tailgate Materials 5.3.5 Drill Holes Before Welding 5.3.6 Weld Using a Jig 5.4 Mount the Tailgate in the Mirror Box 5.4.1 Collimation Bolts 5.4.2 Flotation System Hardware 5.4.3 The Sling and Split Bolts 5.4.4 Side Pins Chapter 6 The Secondary Cage 6.1 Dimensioning the Secondary Cage 6.1.1 The Truss-Tube Advantage 6.1.2 The Inside Diameter of the Secondary Cage 6.2 Constructing the Secondary Cage 6.2.1 Order the Spider and Secondary Holder, and Focuser 6.2.2 Cut the Rings 6.2.3 Make Three Rings for "The Big Ones" 6.2.4 Drill the Strut Seats 6.2.5 Make the Struts 6.2.6 Attach the Struts to the Rings 6.2.7 The Focuser Board 6.2.8 Install the Kydex Light Baffle 6.3 Connecting Ring for "The Big Ones" 6.4 Install the Hardware 6.4.1 Install the Focuser Chapter 7 Building the Mirror Box 7.1 Holding It All Together 7.1.1 Why the Mirror Box is Stubby 7.2 Mirror Box Materials 7.3 Designing the Mirror Box 7.3.1 Height and Width of the Mirror Box 7.3.2 How Balance Affects the Mirror Box 7.3.3 Calculating the Balance Point 7.3.4 The Depth of the Mirror Box 7.4 Balancing the Telescope 7.5 Split Blocks for the Mirror Box 7.6 The Side Bearings 7.6.1 Making the Mirror Box 7.6.2 Cutting the Sides 7.6.3 The Light Baffle 7.6.4 Assembling the Mirror Box 7.6.5 Side Bearing Dimensions 7.6.6 Bonding Flat Panels of Plywood 7.6.7 Constructing the Side Bearings 7.6.8 Placing the Side Bearings 7.6.9 Mounting the Side Bearings 7.7 To Shortcut or Not To Shortcut? 7.8 The Dust Cover Chapter 8 The Truss Tube 8.1 How to Build a Serious Truss Tube 8.1.1 Flexure in Truss Poles 8.1.2 The Diameter of the Truss Poles 8.1.3 The Length of the Truss Poles 8.2 Attaching Truss Poles to the Mirror Box 8.2.1 Overview of Pole Sockets 8.2.2 Wooden Split-Block Sockets 8.2.2.1 How to Make Split-Block Sockets 8.2.2.2 Simplified Split Block Sockets 8.2.2.3 Fancy Cam-Action Pole Sockets 8.2.2.4 Strap and Channel Sockets 8.3 How to Align Truss Pole Sockets 8.4 Attaching Truss Poles to the Secondary Cage 8.4.1 The Crushed Tube Method 8.4.2 The Threaded-Insert Method 8.4.3 The Offset-Bracket Method 8.4.4 The Seats and Wedges Method 8.4.4.1 Making Pole Seats 8.4.4.2 Making Pole Wedges Chapter 9 Bearings 9.1 How Dobsonian Bearings Work 9.1.1 What is Friction? 9.1.2 Friction in the Altitude Bearings 9.1.3 Friction in the Azimuth Bearings Chapter 10 The Rocker and Ground Board 10.1 Sizing the Rocker 10.2 Rocker Construction 10.2.1 Ground Board 10.2.2 Ground Boards for "The Big Ones" 10.3 Constructing the Ground Board 10.3.1 The Azimuth Pivot 10.3.2 How to Make the Pivot Bolt 10.3.3 Installing the Pivot Bolt 10.3.4 Installing Teflon Bearing Pads 10.3.4.1 Calculating the Size of the Altitude Bearing Pads 10.3.4.2 Calculating the Size of the Azimuth Bearing Pads 10.4 A Handy Option: Bearing Locks 10.5 Handles for Portability 10.5.1 "It Rolls On Air" 10.5.2 Attaching Handles to the Rocker 10.6 Handling the Big Ones Chapter 11 Assembly and Troubleshooting 11.1 Last-Minute Preparations 11.2 Installing the Optics 11.2.1 Center-Dot the Primary 11.2.2 Center Dot the Secondary Mirror 11.2.3 Install the Primary Mirror 11.2.4 Install the Secondary Mirror 11.2.5 Adjust the Sling 11.2.6 Collimate the Optics 11.3 Set-Up, Use, and Take-Down 11.3.1 Set Up 11.3.2 Using the Telescope 11.3.2.1 Balance 11.3.2.2 Bearing Surfaces 11.3.2.3 Dew 11.3.2.4 Ventilation 11.3.2.5 Safety Precautions 11.3.3 Take-Down 11.4 Cleaning the Optics 11.5 Troubleshooting 11.5.1 Too Little Focus In-Travel 11.5.2 Sticking Poles and Blocks 11.5.3 Telescopes and Moisture Chapter 12 Using Big Dobsonians 12.1 Eyepieces 12.2 Filters 12.3 Finders 12.3.1 The Telrad Finder 12.3.2 Finder Telescopes 12.3.3 Get Two Finders 12.3.4 Jumbo Finders 12.3.5 Digital Setting Circles 12.4 Electrical Accessories 12.4.1 Dew Zappers 12.4.2 Heat Ropes 12.4.3 Portable 12-Volt Power 12.4.4 Marine Batteries 12.4.5 Power on the Secondary Cage 12.5 Keeping Warm and Dry 12.5.1 Warm Clothing 12.5.2 Keep Warm with Heat Packs 12.6 Eliminating Stray Light 12.6.1 The Light Shroud 12.6.1.1 Sewing a Shroud 12.6.1.2 Installing the Shroud 12.6.2 Focuser Baffling 12.6.3 The External Light Baffle 12.6.4 The Tailgate Cover 12.7 Telescope Covers 12.7.1 Mirror Box Dust Cover 12.7.2 Hat Box for the Secondary Cage 12.7.3 Secondary Mirror Cover 12.7.4 The Telescope Cover 12.8 Dark Observing Sites 12.8.1 Why You Need a Dark Site 12.8.2 Site Selection 12.8.3 Human Factors Chapter 13 Epilog: Making a Small Telescope 13.1 Materials You Need 13.2 Overview of Construction 13.3 Begin with the Tube 13.3.1 The Primary Mirror Cell 13.3.2 Locate the Mirror Cell 13.3.3 Finish the Tube 13.3.4 Add End Rings 13.3.5 Assemble the Tube 13.4 The Mounting 13.4.1 Build the Tube Cradle 13.4.2 Side Bearings 13.4.3 Locate the Tube Balance Point 13.4.4 Construct the Rocker 13.4.5 Make the Ground Board Appendix A Wood as a Structural Material A.1 The Properties of Plywood A.1.1 Types of Plywood A.1.2 The Stiffness of Plywood A.2 Selecting Plywood for Telescopes A.2.1 Hardwood Veneer Hardwood Core Plywoods (HVHC) A.2.2 Hardwood Veneer Softwood Core Plywoods (HVSC) A.2.3 Softwood Veneer Softwood Core Plywoods (SVSC) A.2.4 Particle Board Appendix B Grinding, Polishing, and Figuring Large, Thin Mirrors B.1 Obtaining a Mirror Blank B.1.1 Porthole Glass: the Classic Choice B.1.2 Pyrex Sheet Glass B.1.3 Choose the Mirror Diameter B.1.4 Choose the Mirror Thickness B.1.5 Choose the Focal Ratio B.2 Grinding Tools B.2.1 Solid and Built-up Tools B.2.2 Segmented Tools B.3 Prepare a Suitable Work Area B.4 Preparing for Grinding B.4.1 Facing the Blank B.4.2 How to Prevent Astigmatism B.4.3 Bevel the Edge B.4.4 Grinding Strokes B.5 Rough Grinding B.6 Fine Grinding B.6.1 Fine Abrasives B.6.2 Getting a Sphere B.6.3 Going on to #220 B.6.4 The Fine Side of Fine Grinding B.7 Preparing to Polish B.7.1 Pitch B.7.2 Polishing Agents B.7.3 Pitch Base B.8 Making the Pitch Lap B.8.1 Grooving the Lap B.8.2 Pressing the Lap B.9 Polishing B.9.1 Judging the "Feel" of the Lap B.9.2 Holding the Lap B.9.3 Completing the Polish B.10 Testing B.10.1 Test Stand and Testing Tunnel B.10.2 Begin Testing Early B.10.3 Testing for Astigmatism B.11 Figuring B.11.1 Goals in Figuring B.11.2 Rating Telescope Mirrors B.11.3 Do the Best You Can B.12 Test Methods B.12.1 Testing the Sphere B.12.2 The Sphere and the Paraboloid B.12.3 Star Testing B.12.3.1 Doing a Star Test B.12.3.2 Interpreting the Star Test B.14.4 Applying a Null Test B.14.5 Reading a Ronchi Screen B.13 The Art of Figuring 24 B.13.1 High, Low, Long, Short B.13.2 Figuring Laps B.13.3 Figuring Strokes B.13.3.1 The Long, Straight, Central Stroke B.13.3.2 The W Stroke B.13.3.3 Tangential Strokes B.13.3.4 Strokes for Small Polishers B.13.4 Correcting a Low Edge B.13.5 Correcting a Turned-Down Edge B.13.6 Correcting High Zones B.13.7 Correcting Low Zones B.16 A Few Final Words Appendix C Digital Setting Circles C.1 A Bit of History C.2 How Digital Circles Work C.3 Accurate Circles Need an Accurate Telescope C.4 Installation C.4.1 Mounting the Azimuth Encoder C.4.2 Mounting the Altitude Encoder C.4.3 Mounting the Computer C.5 General Advice Appendix D Equatorial Platforms Appendix E Resources and Suppliers E.1 Aluminum tubing E.2 Foam tube insulation E.3 Double-sided tape E.4 Specialty tools, knobs and latches E.5 Threaded inserts E.6 Levelers (collimation knobs) E.7 Felt tabs and floor protector pads (mirror cell pads) E.8 HVHC plywood (Hardwood Veneer Hardwood Core) E.9 Sliders or cord locks and sling webbing E.10 Heat ropes E.11 Heat paks E.12 Black Ripstop Nylon (for the light shroud) E.13 Kydex plastic for the light baffle E.14 E.14 Etched virgin Teflon E.15 #1782 Stardust Quarry Finish Formica E.16 #4552-50 Ebony Star countertop laminate E.17 Glassboard (bead board or fiberglass reinforced panel) E.18 Self-tapping threaded wood inserts E.19 Cam levers E.20 12-Volt cooling fans E.21 Ladders (for big telescopes) E.22 Small parts E.23 Epoxy resins E.24 Loading ramps, pneumatic wheels for wheelbarrow handles, and marine trailer jacks E.25 Black aperture f/ratio labels E.26 Plastic grommets for light shroud E.27 Duct tape E.28 Collimation tools E.29 Commercial Components for Telescope Making E.29.1 Optics, focusers, digital setting circles, eyepieces, Telrads E.29.2 Spiders and secondary mirror holders E.29.3 Cast aluminum poles seat, clamping wedges, side bearings E.51 Mirror Making Supplies E.51.1 Pyrex glass E.51.2 Kerr dental plaster E.51.3 MicroGrit abrasives E.51.4 Optical pitch E.51.5 Ronchi screens for mirror testing Bibliography Afterword Index
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