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Code Number: 6A65.34
Demo Title: Astigmatism
Condition: Good
Principle: Lens Distortion and Correction
Area of Study: Optics
Equipment:
Optics Table, Slide Projector (Distant Light), Astigmatism Plate (Cork Mounted in Optics Table), and Cylindrical Lens.
Procedure:
NOTE: Placement is critical here!!
Place the astigmatism plate that is in the round holder at 15 cm distance from the camera. Place the eye chart at a distance of 24 cm from the camera. Put the cylindrical lens right up against the side of the astigmatism plate that is farthest from the camera and focus the camera on the eye chart. Remove the lens and observe the eye chart with the astigmatism. Correct the astigmatism by putting the cylindrical lens back up against the astigmatism plate as shown.
The Pasco model will show astigmatism and astigmatism correction quite well using the two lenses in the kit that are just for that purpose. You will need to project a very bright picture onto a screen with the slide projector. Look at this image using the eye model with the astigmatism lens in place. The image on the "retina" viewing screen will be distorted. Place the correcting lens in the unit and rotate this lens until the image is sharp and clear on the "retina". The image on the retina viewing screen will need to be projected to the class using a video camera.
References:
- Mark Riegel and Brian Holmes, "Model of Astigmatism", TPT, Vol. 26, #2, Feb. 1988, p. 96.
- "Optical Astigmatism Model", TPT, Vol. 10, #4, Apr. 1972, p. 201, also A Potpourri of Physics Teaching Ideas- Optics and Waves, p. 221.
- Daniel Nahshol, "Optical Aberrations - Demonstration and Measuring", AJP, 33, #11, Nov. 1965, p. 970.
- O-370: "Stops - Apertures & Obstacles", DICK and RAE Physics Demo Notebook.
- L-51: Richard Manliffe Sutton, Demonstration Experiments in Physics.
- John H. Moore, Christopher C. Davis, and Michael A. Coplan, "Cylindrical Lenses", Building Scientific Apparatus 2nd Edition, p. 148 - 149.
- John H. Moore, Christopher C. Davis, Michael A. Coplan, "Astigmatism and Field Curvature", Building Scientific Apparatus 2nd Edition, p. 146 - 147.
- C. Harvey Palmer, "Experiment A13: The Off-Axis Aberrations of Lenses", Optics - Experiments and Demonstrations, John Hopkins Press, 1962.
- The Queen Catalogues Vol. I, Catalogue of Ophthalmological Instruments, Astigmatism, p. 15.
- The Queen Catalogues Vol. I, Catalogue of Ophthalmological Instruments, No. O-249, p. 99.