Group Homework 1.9 (Answers)1. Which optical device is similar to the binoculars?

Optical devices that are similar to the binoculars, which magnifies distant objects include telescopes (used to view distant objects in space), glasses (specifically the one which allows the person to see distant objects clearly), and the camera (its lens provide the user the skills to zoom or magnify a distant object, however Polaroid cameras dont have zoom buttons so they are not included).

2. Which part/s of the binocular allows you to see the image in its correct orientation?

The two lenses, the objective and the eyepiece, enable the user of the device to see the magnified image; yet, the prisms let you see a correctly oriented image when you look through a pair of binoculars. There are two types of prisms in common use, Porro prisms and roof prisms. The prisms serve as the corrector for the image formed by the objective lens (without prisms, obj. lens will form an inverted and laterally reversed image), which will give a corrected version of the image to the eyepiece. Now, the eyepiece will magnify it, so the final image formed is upright and enlarged. For more information, refer to the diagram below:

Source: Birdwatching.com

3. What kind of lens is used as the objective lens of a binocular used for hunting and fishing?

Usually, hunting and fishing binoculars needed greater magnification and resolution for an image than the normal binoculars. The objective lens of these kinds of binoculars should be a large convex lens, specifically a large biconvex lens. This lens has a thin edge, which allows more light to pass through the lens. Moreover, the lens also consist of a thicker middle part since all the light rays that will pass through the lens will converge in the thick part of the lens, to form the image. (Microsoft Premium Encarta, 2009)

However, other combinations for the objective lens of a binocular are being used by other manufacturer of these optical devices. It uses a combined convex and concave lenses for the image to minimize color fringing, resulting in clearer images. Moreover, they have the properties of a biconvex lens, as stated in their composition. (Nikon.com)

(Combined lenses: Achromatic doublet lens: a combination of concave and convex lens with lesser chromatic aberrations)

4. What kind of lens is used in the eyepiece of a binocular used for hunting and fishing?

The usual assembly for the eyepiece that is used in binoculars is the Kellners lenses combination. It is composed of an achromatic doublet (combination of a convex and a concave lens which provide lesser chromatic aberrations; acts like a biconvex lens and a singlet field lens (plano-convex or commonly used as a biconvex lens). The diagram below shows an example of the lens:

Generally, the eyepiece is made up of convex lenses.

5. Using the same binocular, where should the image from the objective lens fall with respect to the eyepiece?

If the first image formed by the objective lens will be corrected by the prisms, then the second object will be the corrected first image (so the image will be upright, smaller, and real). The second object must be between F2 and V2, as stated in the diagram, so it will become upright, enlarged, and virtual:

(Let F be F2 and P be V2 because this is the second part of the real diagram.)

6. Using the same binocular in no. 4, where should the image from the eyepiece be so that the image is on the same side of the object?

Similarly, the image from the eyepiece is formed in a placed somewhere between (but not in between) the radius of curvature and F2 (showed in diagram in no. 4) so the image will be on the same side as the object (virtual).

7. What kind of image is formed by the objective lens by a far away object using the same binocular above?

The objective lens will form an inverted, real, and smaller image. As stated in the question, the object is very far from the binoculars, so if we are going to put it on graphical situation, the object can be at infinity or beyond 2F (radius of curvature). Look at the diagram below for more information:

8. What kind of image is formed by the eyepiece and what are the complete image characteristics?

The image corrected by the prisms (upright image) will be the object for the eyepiece. The purpose of the eyepiece is to magnify the object, so the final image will have an enlarged and upright characteristic. In addition to that, the image formed is virtual, since convex mirrors would always produce a virtual image.