Is the objective lens of an astronomical telescope a convex lens

That's right. For refracting astronomical telescopes, they can be divided into Galilean telescopes and Keplerian telescopes, both of which have convex lenses.

1.Galilean telescope.

In 1609, Galileo made a telescope with a caliber of centimeters and a length of about meters. He used plano-convex lenses as objective lenses and concave lenses as eyepieces, an optical system called a Galilean telescope. Galileo Galilei pointed the telescope to the sky and made a series of important discoveries, and astronomy entered the telescope age.

2.Keplerian telescopes.

In 1611, the German astronomer Kepler used two biconvex lenses as objective lenses and eyepieces respectively, which significantly improved the magnification, and later people called this optical system Keplerian telescope. There are still these two forms of refracting telescopes used by people, and astronomical telescopes are Kepler.

Not really. The lens structure of astronomical telescopes is very sophisticated, and even for common telescopes, the objective lens is composed of at least one convex lens and one concave lens, and the chromatic aberration is eliminated by precisely matching the surface shape and material (refractive index) of the two lenses; There are more lenses that make up the eyepiece, and the commonly used Proso eyepiece is made up of two convex lenses and two concave lenses.

In addition, the objective lens of a reflecting telescope is a concave mirror, and the eyepiece is a convex lens. The catadioptric telescope also has a meniscus corrector mirror (maca) or a complex curved mirror (schka) before the primary mirror.

Of course, in terms of the overall effect, it is right that the objective lens and eyepiece of an astronomical telescope are equivalent to a convex lens.

The telescope only has one objective, so you probably have to take it apart.

Achromatic objective assembly.

The achromatic objective of a refracting telescope has a variety of optical configurations, such as double cementing, double separation, triple separation, etc. It is estimated that you have taken apart a double split achromatic objective, and you did not look closely at the two lenses that make up the objective after disassembling it, and did not notice the logo on it.

Two lenses of a double-separate achromatic objective.

See image above. The purpose of these three supports is to separate the two optical surfaces of the two lenses close to each other, creating an air gap between them. The thickness of the air gap, or the distance between these two optical surfaces, is equal to the thickness of the support sheet.

At this point, you should understand: the surface with the support is one of the two surfaces where the two lenses are close to each other. The other lens on the curvature.

The side that is the same as this surface (which needs to be carefully observed or measured) is the side that is relatively assembled when the objective lens is assembled.

<> note that when combining two lenses, the coaxial light center of the lens must be considered, and it is not possible to measure the light center of the lens under general amateur conditions. At this time, it is necessary to observe whether there are any markings on the edge of the lens similar to those shown in the two pictures above, which were specially drawn by the optical factory after completing the optical center test. Try to align them when combining.

Finally, it is best not to disassemble the lens base of the telescope objective lens (especially the high-precision ED APO objective), and when it must be disassembled (for example, water ingress in the air gap of the lens needs to be removed), it is best to contact the original purchase channel or find a professional optical repair service provider to ensure that the lens coating will not be scratched and worn during the disassembly process, and the optical accuracy will be completely restored after reassembly.

Incorrect. The telescope introduced in the textbook is only one type of telescope, which uses two sets of convex lenses. And the objective lens is a convex lens. Whereas, large astronomical telescopes are usually reflective, and the objective lens is made of concave mirrors.

An objective lens is a lens group that combines several lenses. The purpose of the combination is to overcome the imaging defects of individual lenses and improve the optical quality of the objective lenses.

The lack of finger magnification of the microscope mainly depends on the objective lens, the quality of the objective lens directly affects the quality of the microscope image, it is the main component that determines the resolution of the microscope and the degree of imaging clarity, so the correction of the objective lens is very important.

Astronomical telescopes are generally made with two convex lenses (Kepler telescopes), and telescopes made of convex lenses and concave lenses (Galilean telescopes) are not suitable for astronomical telescopes because of their relatively small field of view.

Galilean telescope: The objective is a converging lens and the eyepiece is a telescope with a divergent lens. The real image formed by the refraction of light through the objective lens is on the focal point behind the eyepiece (near the back of the human eye), which is a virtual image of the eyepiece, so it is refracted into an amplified upright virtual image.

The magnification of the Galilean telescope is equal to the ratio of the focal length of the objective lens to the focal length of the eyepiece. The advantage is that the lens barrel is short and can be orthodox, but it has a relatively small field of view. The device that juxtaposes two Galilean telescopes with low magnification and uses a bolt button in the middle to adjust their clarity at the same time is called a "theater viewing mirror"; Because it is easy to carry, it is often used to perform and so on.

The telescope invented by Galileo occupies an important place in the history of human understanding of nature. It consists of a concave lens (eyepiece) and a convex lens (object). Its advantage is that it has a simple structure and can be directly formed into a positive image.

You can build a Galilean telescope for a very low cost. Buy a spectacle lens with a larger diameter and focal length from a stationery store as an objective lens and a lens with a smaller focal length and diameter as an eyepiece. By putting two lenses in a cardboard tube with glue and small slots, and making a simple pedestal, a telescope was made that could see the mountains of the moon, the stars of the Milky Way, and the moons of Jupiter.

Think about it, Galileo used this to discover. But remember, don't look directly at the sun through a telescope to avoid burning your eyes from the heat! One of the annoying drawbacks of Galileo's refracting telescopes was that they produced "false colors" around bright objects.

The crux of the "false color" is that what is commonly called "white light" is not white light at all, but a chain of light that mixes all the colors that make up the rainbow, from red to violet. When the beam enters the objective lens and is refracted, the various colors of light are refracted to different degrees, so the focal point of the imaging is also different, and blur is created.

Whether a telescope is composed of a convex lens or a concave lens depends on the situation.

A refracting telescope is made up of two convex lenses; The objective lens of the reflecting telescope is a concave lens, and the eyepiece is a convex lens; Catadioptric is made up of two convex lenses and two concave mirrors.

A telescope is an optical instrument that uses lenses or mirrors and other optical devices to observe distant objects. Light rays that are refracted through a lens or reflected by a concave mirror allow them to enter a small hole and converge for imagery, and then pass through a magnifying eyepiece to be seen.

The first purpose of a telescope is to magnify the opening angles of distant objects, so that the human eye can see details with smaller angular distances. The second function of the telescope is to feed the beam of light collected by the objective lens that is much thicker than the diameter of the pupil (up to 8 mm) into the human eye, allowing the observer to see faint objects that were previously invisible.