1. Optical Instruments
Or Seeing is Believing

2. Review of Converging Lens Images
Object Distance from Lens
Real or Virtual
Magnified or Reduced
Erect or Inverted
Less than 1 focal length
Virtual
Magnified
Erect
Between 1 and 2 focal lengths
Real
Magnified slightly
Inverted
Greater than 2 focal lengths
Reduced
Questions: make a chart that shows the three types of images a converging lens can form.

3. The Camera Final image is reduced, inverted and real
Uses one converging lens
Focusing is accomplished by changing the distance between the lens and sensor
Small distance for far away shots
Large distances for close-ups
Spherical aberration of lens reduced by using diaphragm (f stop)
Chromatic aberration fixed by achromatic lens
Questions: What type of lens is used in a camera? What type of image is produced? When focusing on a far away object do you want the maximum or minimum distance between the lens and sensor? How does a camera control spherical and chromatic aberration?

4. Microscopes and Telescopes
Both devices use two converging lenses called the eyepiece and objective.
Telescopes objective lens is largest
Microscopes eyepiece is larger
Image from objective is real, reduced and inverted and is located within 1 focal length of the eyepiece
Image from eyepiece is virtual, magnified and still inverted when compared to the original object.
Variations for photography
Questions: Draw the lens arrangement of a telescope. Where is the image from the objective located relative to the eyepiece lens? Describe the final image from the telescope. How is a microscopes lens arrangement different? What changes must be made for photography for these instruments?

5. The Human Eye
Cornea, vitreous humor, and crystalline lens both act as converging lens producing image that is real, reduced and inverted.
Iris regulates light coming into eye
Muscles squeeze and stretch lens and cornea to focus.
Brain learns to turn inverted image 1-2 weeks.
Retina consists of rods (black and white) and cones (colors).
Questions: What structures form a lens in the human eye? What type of lens does it form? How does the eye focus? Describe the image the eye forms. Why don’t we see everything upside down? What causes color blindness?

6. Eye Defects Near Sightedness Can see near but not far
Parallel rays from far objects focus in front of retina (eye is too darn long)
Need diverging lens in center and no lens on outside
Gets worse with age
Far sightedness
Can see far but not near
Divergent rays from close objects are focusing behind retina (eyes too darn short)
Need converging lens on outside and no lens for inside rays
Gets better with age
Questions: What can a near sighted person see and not see? Are their eyes too darn long or short? Draw the type of lens they need. What is an astigmatism? What shape is the lens that is needed to correct this defect?
Astigmatism: different curvatures in different directions, need barrel shaped lens to correct