Geometric method to measure astigmatism aberration at astronomical telescopes

Area of Science:

• Optical astronomy
• Telescope aberration analysis

Background:

• Accurate measurement of wavefront aberrations is crucial for optimal telescope performance.
• Astigmatism is a common aberration affecting image quality in optical systems.

Purpose of the Study:

• To present a simple geometrical method for measuring astigmatism in telescope wavefronts.
• To validate the method's accuracy and compare it with existing wavefront tests.

Main Methods:

• Analysis of the external contour of a slightly defocused star image.
• Derivation of an elliptical edge expression linking root-mean-square (rms) Z22 values to geometric ellipse parameters.
• Testing the method with introduced defocus and astigmatism in observatory telescopes.

Main Results:

• The geometrical method provides comparable results to established wavefront tests.
• The technique can measure astigmatism values as low as approximately 60 nanometers.
• The method does not necessitate the use of auxiliary optical components.

Conclusions:

• The presented geometrical method offers a straightforward and effective way to measure telescope astigmatism.
• This technique enhances the ability to diagnose and correct wavefront aberrations, improving astronomical observations.
• The method's simplicity and lack of need for extra optics make it a practical tool for optical testing.