Who Invented the first microscope?

Credit for the first microscope is usually given to Zacharias Jansen, in Middleburg, Holland, around the year 1595. Since Zacharias was very young at that time, it's possible that his father Hans made the first one, but young Zach took over the production. Details about these first Jansen microscopes are not clear, but there is some evidence which allows us to make some good guesses about them. The above early microscope found in Middleburg, Holland, corresponds to our expectations of the Jansen microscopes.

Microscope

Structure: Made of two lenses, Objective and eyepiece Objective: The object being viewed is

placed just outsidejust outside the focal length of the objective lens. the image thus formed is real, inverted, and enlarged. We will call this image the intermediate intermediate imageimage since it is not the final image viewed in the eyepiece.

An example

Suppose the focal length of the objective is 12mm, and the object is placed at 13cm. The image is then 156cm away from the lens and the magnification is

156/13 = 12 times!

Eyepiece: Work as a magnifying glass, used to view the real intermediate image formed by the objective lens.

To view the image with a relaxed eye (so the light rays entering the eye is parallel), the image must be located at the focal point of the eyepiece.

Shorter the focal length, larger the magnification.

The example continued

Now suppose the eyepiece has a focal length of 50mm. Then it has a magnification power of 25cm / 5cm = 5 times

The total magnification is

12 x 5 = 60 The distance between two lens S =

(156+50)mm = 20.6 cm

Cat flea

Fruit flyneuron

Black ant

Telescope

The incoming rays are parallel and the outgoing rays are also parallel.

Again need two lenses: the objective and eyepiece.

The intermediate image is on the focal plane of the objective. It must be also on the focal plane of the eyepiece.

The total length of the telescope is fo +fe.

Telescope Magnification

To get a large image, fO must be large.

To see the image up close, fE must be small.

The telescope magnification is

Negative because the image is inverted. A large intermediate image means that it is

dimmer. One needs a larger aperture. Thus telescopes are usually specified by their sizes.

eo ff /

Images from Hubble Telescope

How to make the image erect?

Method I: Add another lens

Method II: Galilean telescope:

the eye piece is a diverging lens. fe is negative.

The magnification can be calculated the same way!

eo ff /

Galilean Telescope

A Galilean telescope is defined as having one convex lens and one concave lens. The concave lens serves as the ocular lens, or the eyepiece, while the convex lens serves as the objective. The focal point of the ocular lens is the same as the focal point for the objective lens.

Magnification = fo/fe

Length of the telescope = fo-fe

Small field of viewSmall field of view. A Galilean telescope typically has a field of view of about 15-18 arc minutes. The moon has a diameter of about 30 arc minutes, so the Galilean telescope only reveals approximately one-fourth of the moon's surface at one time.