Take a look at figure 1. What is it? A work of art? Maybe. To paraphrase Picasso: ‘Art is the lie which reveals the truth.’ More prosaically it is simply a three-dimensional diagram depicting ray paths in astigmatic refraction.
Understanding the nature of astigmatic refraction can be a challenge to those new to ophthalmic optics. My motivation to produce a model was to help demonstrate the salient features and to share the construction details should anyone wish to replicate it.
Two-dimensional limitation
Most of us involved with ophthalmic optics will be familiar with two dimensional diagrams similar to the one shown in figure 2. Here we see the location of the principal ‘landmarks’ of an astigmatic beam: the two focal lines and the circle of least confusion. In optical terms the region between the two focal lines is known as the interval of Sturm. In geometrical terms the space bounded by the rays within the interval of Sturm is known as the conoid of Sturm, named after the Swiss-born mathematician Jacques-Charles-François Sturm (1803-55).
Register now to continue reading
Thank you for visiting Optician Online. Register now to access up to 10 news and opinion articles a month.
Register
Already have an account? Sign in here