Lecture Notes: How to Make Your Own Telescope

Introduction

• Making a homemade telescope is possible with basic materials.
• Completed DIY project results in a personal telescope to observe stars and planets.
• Small refractor telescopes are light, portable, and require minimal adjustments, ideal for beginners.
• The project is suitable for school or home science projects.

Understanding Telescopes

• Building your own telescope helps understand the functionality of telescopes.
• Key component: Convex glass objective lens mounted near the front of the telescope tube.
  • Light rays are refracted towards the principal focus inside the tube.
  • The focal length is the distance from the lens center to the principal focus.

Selecting the Eyepiece

• At the far end of the tube, the eyepiece aligns with the principal focus of the objective lens.
• Eyepiece Suggestions: 1.25-inch Plössl eyepiece (~£25).
• The eyepiece refracts light rays into the eye, with a shorter focal length for magnification.
• Magnification calculation: Divide objective focal length by eyepiece focal length.
• Larger aperture of objective allows more light capture.

Selecting the Telescope's Lens

• Small 70mm refractor is useful for observing faint objects.
• Historical telescopes used single convex objective lenses.
• Modern achromatic objectives use doublet lenses to align color spectrums, reducing blurring/halo effects.
• Achromatic lenses are less expensive and more accessible than apochromatic lenses.
• Lenses are available for around £20 for a 60mm lens via surplus companies (e.g., Surplus Shed).

Building the Telescope

• Parts can be sourced from plastic pipes or salvaged from old binoculars.
• Measure lens focal length using a simple setup with a stand and a card.
• Adjust lens position until a focused image is projected.
• Temporary eyepiece stand can confirm optical arrangement.
• Follow PDF guide for tube lengths and assembly steps.

Usage and Mounting

• A tripod (e.g., standard camera tripod) is recommended for stable astronomical observation.
• Consider telescope mounts (altaz or equatorial) for precise guiding.

Tools & Materials Required

• Eyepiece: Medium focal length (e.g., 20mm) Plössl type.
• Tripod: Can use a camera tripod.
• Focuser: 43mm diameter plastic waste pipe.
• Telescope Tube: Larger diameter than objective lens; at least as long as focal length.
• Dew Shield: About 125mm of tube, similar to telescope tube.
• Objective Lens: 60-80mm objective lens from surplus store or salvaged equipment.
• Saw Tools: Handsaw or hacksaw for tubes, coping saw for wooden end.

Conclusion

• Building a telescope is an educational and rewarding project, providing practical insights into astronomy and optics.