Originally Posted by
lensgrinder
In 1804 Dr. William Wollaston published a study that stated that curved meniscus lenses have slightly better imagery than bi-convex.
In 1898 Dr. Franz Ostwalt calculated each power within a range of, about -22.00 D to +7.00 D, to show that a lens with a certain base curve for each power could be made without oblique astigmatism.
Ostwalt’s calculations were done using thin lens equation, therefore, Dr Marius Tscherning re-calculated Ostwalt’s work using thick lens equations. Since an ellipse has two solutions each branch was named Wallaston(steep) and Ostwalt(flat).
The Wallaston and Ostwalt branches show that a lens power(within a certain range) can be made free from oblique astigmatism using two possible curves.
For example a -4.43 made in CR-39 with a 2.0 CT, can be made on a 16.97 BC or a 4.97 BC.
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