一九四零年，美國哲學家莫蒂默‧傑爾姆‧阿德勒 Mortimer Jerome Adler 寫了一本《如何閱讀一本書》的書。其後於一九七二年，美國哥倫比亞大學的教授查爾斯‧范多倫 Charles Van Doren 重新修訂。這本書主要論述如何『通過閱讀』增進『理解力』。《如何閱讀一本書》將閱讀分做四個層次『基礎閱讀』、『檢視閱讀』、『分析閱讀』和『主題閱讀』。並在書後推薦了一系列的『經典名著』。『 目的』是強調閱讀是一種『自主活動』。

───  摘自《如何閱讀□○？？》

 

閱讀最重要的事就是學會閱讀的方法。如是方能自主學習有興趣的知識，得到讀書的樂趣。因此在讀過一系列文本後，相信讀者已能輕輕鬆鬆瀏覽維基百科詞條︰

Refracting telescope

A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long focus camera lenses. Although large refracting telescopes were very popular in the second half of the 19th century, for most research purposes the refracting telescope has been superseded by the reflecting telescope which allows larger apertures. A refractor’s magnification is calculated by dividing the focal length of the objective lens by that of the eyepiece.^[1]

Refracting telescope designs

All refracting telescopes use the same principles. The combination of an objective lens 1 and some type of eyepiece 2 is used to gather more light than the human eye is able to collect on its own, focus it 5, and present the viewer with a brighter, clearer, and magnified virtual image 6.

The objective in a refracting telescope refracts or bends light. This refraction causes parallel light rays to converge at a focal point; while those not parallel converge upon a focal plane. The telescope converts a bundle of parallel rays to make an angle α, with the optical axis to a second parallel bundle with angle β. The ratio β/α is called the angular magnification. It equals the ratio between the retinal image sizes obtained with and without the telescope.^[4]

Refracting telescopes can come in many different configurations to correct for image orientation and types of aberration. Because the image was formed by the bending of light, or refraction, these telescopes are called refracting telescopes or refractors.

Galileo’s telescope

The design Galileo Galilei used in 1609 is commonly called a Galilean telescope. It used a convergent (plano-convex) objective lens and a divergent (plano-concave) eyepiece lens (Galileo, 1610).^[6] A Galilean telescope, because the design has no intermediary focus, results in a non-inverted and upright image.

Galileo’s best telescope magnified objects about 30 times. Because of flaws in its design, such as the shape of the lens and the narrow field of view, the images were blurry and distorted. Despite these flaws, the telescope was still good enough for Galileo to explore the sky. The Galilean telescope could view the phases of Venus, and was able to see craters on the Moon and four moons orbiting Jupiter.

Parallel rays of light from a distant object (y) would be brought to a focus in the focal plane of the objective lens (F′ L1 / y′). The (diverging) eyepiece (L2) lens intercepts these rays and renders them parallel once more. Non-parallel rays of light from the object traveling at an angle α1 to the optical axis travel at a larger angle (α2 > α1) after they passed through the eyepiece. This leads to an increase in the apparent angular size and is responsible for the perceived magnification.

The final image (y″) is a virtual image, located at infinity and is the same way up as the object.

Optical diagram of Galilean telescope y – Distant object ; y′ – Real image from objective ; y″ – Magnified virtual image from eyepiece ; D – Entrance pupil diameter ; d – Virtual exit pupil diameter ; L1 – Objective lens ; L2 – Eyepiece lens e – Virtual exit pupil – Telescope equals ^[5]

 

解釋折射式望遠鏡成像原理的吧☆

遠物→do = do’ – f1→F1面→望遠鏡→F2面→z=z’-f2→眼→e→成像

pi@raspberrypi:~ M = \frac{f_1}{f_2} \frac{1}{e} = \frac{1}{f} - \frac{1}{\frac{d_o' - f_1}{M^2} + (z' -f_2)} }$ 。