Newton's Reflecting Telescope

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Experimental History
Research Topic: Newton’s Reflecting Telescope

Patrick Doan
Kevin Le
Kevin Tumang

Principle Aim: To construct a recreation of the Galilean refracting telescope and a Newtonian reflecting telescope

Aim: To recreate Newton’s experiment in building a reflecting telescope, aiming to further the field of optics. We hope to use the theory studied in this experiment and produce a working Newtonian telescope (that Newton designed). He wanted to create a telescope that was not affected by chromatic aberration and thus further the field of optics. We also aim to try to remove the problem of spherical aberration that Newton had trouble with in building his telescope.


We are building a Newtonian reflecting telescope that doesn’t suffer from chromatic aberration. It was Newton who built the first reflecting telescope that didn’t suffer from chromatic aberration. It was also Newton who devised the idea of building a telescope that consisted of mirrors rather than just lenses. The problem that had stuck with astronomers at the time was chromatic aberration and spherical aberration. A note for the record is that Newton did not invent the reflecting telescope but it was Scottish mathematician James Gregory who made the apparatus in around the 1660s. It is good to note that Newton did not build the telescope to observe the sky and planets like Galileo but did it to further study the field of optics. Our reflecting telescope is similar to Newton’s that he made in 1668. Both ours and Newton’s consisted of a flat mirror, a spherical mirror and a convex lens. Our telescope also suffered from the repercussions of spherical aberration. Below is a drawing of the concept of our telescope and Newton's telescope:

Drawing 1

Isaac Newton (1642-1727)

Isaac Newton, often referred to as Sir Isaac Newton, was born at Woolsthorpe, near Grantham in Lincolnshire. He was a mathematician and physicist and was one of the foremost scientific intellects of all time. He attended school at Woolsthorpe and entered Cambridge University in 1661 to lecture as a professor in mathematics. He remained at the university, lecturing for a majority of the time, until 1696. Throughout two to three years of his time, Isaac put intense mental effort into preparing Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) which is often referred to as the Principia, although he created this around 1670 this was not published until 1687. Isaac Newton is also well known for his work on light and the spectrum. He also used those topics to form a major part of his book Optiks which was published in 1704. one of the main repercussions of this book was Newton’s development on the reflecting telescope. Isaac Newton’s works were known to be one of the greatest contributions to science ever made by an individual.

The scientific theory behind our experiment is that light coming into a tube is reflected from the primary spherical concave mirror into a secondary flat plain mirror at an incline of 45°. The light on the flat mirror is then reflected to a convex eyepiece lens which forms an image.


• Large cardboard tube (diameter of 154mm)
• Large concave mirror
• Small flat plain mirror
• Cardboard tubes (3 and 4 cm in diameter)
• Power drill
• Epoxy putty
• Convex lens (biconvex 5cm FL)
• Tape measure (construction and fashion)
• Tri-square
• Masking tape
• Black spray-paint
• Felt fabric
• PVA glue
• Saw
• Chisel and mallet
• Skewers
• 2B pencil
• Blu-tack


Testing the Focal Length of the Mirror (the sun test)

1. The mirror was held up facing towards the sun.
2. A piece of card was held in front of the mirror as to form a screen for the converging light. 3. The card was moved gradually back away from the mirror and towards the sun so as the...
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