Introduction to the types of astronomical telescope
eyepieces
1. Huygens eyepiece (H ??
Designed by Dutch scientist Huygens in 1703, it consists of two plano-convex lenses, the front is the field lens and the back is the eyepiece, their convex surfaces are all facing one end of the objective lens, and the focal length of the field lens is It is generally 2-3 times the eyepiece, and the lens spacing is half the sum of their focal lengths. The Huygens eyepiece has a field of view of about 25-40 degrees. In the past, the Huygens eyepiece was the first choice for small refractors, but with the increase of the optical power of the telescope, its shortcomings of small field of view, low contrast, chromatic aberration, and spherical aberration were gradually exposed. Used for microscope eyepieces.
2. Ramsden Eyepiece (R)
Designed in 1783, it is also two The two-group structure of the film consists of two plano-convex lenses with opposite convex surfaces and the same focal length. The spacing is 2/3-3/4 of the sum of the focal lengths of the two. The chromatic aberration is slightly larger, the field curvature is significantly reduced, and the field of view is about 30-45 degrees, which is rarely used at present.
3, Kellner eyepieces (K, RKE)
is the Ramsden eyepiece It was developed on the basis of , and appeared in 1849. The main improvement was to change the single-piece eyepiece to a double cemented achromatic lens, which greatly improved the improvement of chromatic aberration and edge image quality. The field of view reached 40-50 degrees, low It has a comfortable exit pupil distance at magnification, so it is widely used in some medium and low magnification telescopes, but it does not perform well at high magnification. In addition, the field lens of the Kellner eyepiece is close to the focal plane, so that the dust on the field lens is easy to image and affects the observation, so special attention should be paid to cleaning.
An American company further improved the Kellner eyepiece and developed the RKE eyepiece, whose edge image quality is better than the classical structure.
4. Abbe’s undistorted eyepiece (OR)
Founded by Zeiss, Germany in 1880 One of the people, Abbe’s design, is a four-piece two-group structure, in which the field lens is a triplet lens, and the eyepiece is a plano-convex lens. The eyepiece successfully controls chromatic aberration and spherical aberration, and reduces ghost images and field curvature to difficult levels. The degree of perception, it also has a flat field of view of 40-50 degrees and sufficient exit pupil distance, has good performance at various magnifications, and has been widely used.
5. Elephant wide-angle eyepiece (ER)
Developed in 1917, it is a special Designed for military telescopes that require a large field of view, it is the originator of all subsequent wide-angle eyepieces. It has a structure of 5 elements in three groups, and the field of view is as high as 60-75 degrees. It is very suitable for observing deep sky objects. Due to the astigmatism at the edge, it is not suitable for high-power design, and its performance at low power is very good.
6. Prussell eyepiece (PL)
Also known as symmetrical eyepiece. It is composed of exactly the same two sets of double cemented achromatic lenses. Its parameter performance is comparable to that of OL eyepieces, but it has a larger exit pupil distance and field of view, lower cost, and is suitable for all magnifications. It is currently the most widely used. A variety of improved eyepieces have been derived.
7. Nagler eyepiece
A high-end eyepiece designed by Americans in 1979, It has an amazing field of view of 82 degrees, excellent edge image quality and comfortable exit pupil distance, as well as complex structure and high price, and it weighs more than one kilogram.