Также было интересно узнать о том, что "Окуляры типа Наглер - единственные коммерчески имеющиеся в наличии на маркете, у которых конструкция пошла на дороговизну исправления астигматизма окуляра ( и они соответственно дороги). Вот почему дизайн Наглера так хорошо работает на светосильных ньютонах"(с)
Я постоянно в душе чувствовал, что не зря у всех виденных мною американских заядлых "добсонистов", 80% окулярного арсенала - окуляры Телевью. Пусть даже их у владельца всего два-три. У меня интуиция на железо и стекло.
A Note On Eyepiece Aberrations
In the above discussion it is assumed that eyepiece aberrations do not contribute significantly to the final image quality of the telescope/eyepiece system. In reality this is rarely the case. When examined independent of a telescope, the dominant aberrations in most eyepiece designs are field curvature and astigmatism. Usually, these eyepiece aberrations are larger than the telescope's comatic aberration and they are the aberrations most prominent in the image. In the eyepiece, the combination of astigmatism and coma give the star a squashed, V-shaped appearance. The effect of eyepiece field curvature is to cause stars at the edge of the fov to appear slightly defocused when stars at the center of the fov are in sharp focus.
To understand why eyepiece aberrations are so large, note that the eyepiece is actually a small refracting telescope being used in reverse. The eyepiece is designed to re-collimate 'point-like' star images produced by the telescope so that your eye can refocus them onto your retina. Now consider that most modern eyepiece designs have an apparent fov of between 60 and 80 degrees! Correcting astigmatism and field curvature over such a wide fov requires a complex and expensive eyepiece design. The Nagler eyepiece is the only commercially available design that goes to the expense of correcting eyepiece astigmatism (and they are priced accordingly). That is why the Nagler design works so well with fast Newtonians.
About the Author
James Mulherin is the president of Optical Mechanics and a master optician. James manages the optics shop at Optical Mechanics and is a leading expert in the design and fabrication of astronomical optics.
