19.3 Optical Instruments

Think about this… Picture in your head the stars at night. Then, picture what a galaxy looks like. How do you know what a galaxy looks like? Due to optical instruments, like the telescope, you can see more details than just with your unaided eye.

Our Goals… To understand different optical instruments and how they help us see more details. We are going to focus on: The telescope The camera The microscope

Telescopes The universe is so vast that the light coming from the farthest stars has traveled billions of years before it reaches Earth. A telescope helps us see the light from distant objects. In Greek, the word teleskopos means “seeing from a distance.” There are two main types of telescopes, reflecting and refracting.

Reflecting Telescopes Reflecting telescopes use mirrors and convex lenses to collect and focus light. Light first strikes the large concave mirror and is brought to a focus.

Reflecting Telescopes Then, this focused light is reflected again by an angled mirror and forms a real image. The convex lens of the eyepiece then enlarges the image.

Refracting Telescopes Refracting telescopes use convex lenses to collect and focus light. Light from a distant object enters the telescope by passing through the first convex lens, called the “objective lens.”

Refracting Telescopes This forms a real image inside the telescope. Another convex lens in the eyepiece then magnifies this real image.

Refracting Telescopes There are many different problems with lenses that make refracting telescopes less powerful than reflecting telescopes. For instance, all lenses have some sort of defect that can cause aberrations - distortions in an image.

Defects of Lenses Spherical aberration: when light passed through the edges of a lens focuses at slightly different places. You can correct this by blocking the edges.

Defects of Lenses Chromatic Aberration: Different colors of light focus at different places.

Cameras A camera is an optical instrument that records an image of an object. These days, cameras are everywhere and are found in different devices. However, no matter what type of camera, it uses the same basic principles. All cameras focus light with an opening or lens and form an image that is recorded on film or by a sensor.

Pinhole Cameras You can make a camera that has just a pin-hole. Light from a scene passes through this single point and projects an inverted image on the opposite side of the box.

Film Cameras The modern film camera is a little more complex than a pinhole camera. The lens focuses the incoming light rays.

Film Cameras Then, a mirror that is in front of the film reflects that light to another mirror or prism that reflects the light again to the viewfinder (so you can see what you are taking a picture of).

Film Cameras Then, when you take the picture, the shutter button is pressed and the mirror that was in front of the film flips up. The shutter briefly opens to let the focused light strike the film.

Film Cameras The focused light reacts with a light-sensitive chemical coating on the film. This chemical coating records the real image.

Digital Cameras Just like a conventional camera, it has a series of lenses that focus light to create an image of a scene.

Digital Cameras But instead of focusing this light onto a piece of film, it focuses it onto a semiconductor device that records light electronically. A computer then breaks this electronic information down into digital data.

Microscopes A microscope is an optical instrument that uses lenses to provide enlarged images of very small, near objects. One common type of microscope is called the compound microscope. Compound microscopes is “compound” because it uses two lenses.

Microscopes The first lens is a convex lens called the objective. This lens produces and enlarged, upside-down, real image.

Microscopes This image then become the “object” for the second convex lens called the eyepiece. The eyepiece is positioned so that you will see an enlarged, virtual image of the object.