Last time: Built a telescope (1 each!)

Last time: Built a telescope (1 each!) 1. Got parts: TWO lenses, cardboard tubes, two red caps, foam, little tube, white paper disk. 2. Assembled the parts into a useful optical instrument, a telescope! 3. You will need this telescope for HW12! Come and get your set if needed!! 1

Physics 1230: Light and Color Chuck Rogers, Charles.Rogers@colorado.edu Ryan Henley, Valyria McFarland, Peter Siegfried physicscourses.colorado.edu/phys1230 Lecture 27: More microscopes and telescopes and binocular vision Project Progress Report feedback still coming. Online and Written HW12 next week. 2

Physics 1230: Light and Color Chuck Rogers, Charles.Rogers@colorado.edu Ryan Henley, Valyria McFarland, Peter Siegfried physicscourses.colorado.edu/phys1230 Lecture 27: Plan to pause early today for folks to check in about supplies, telescopes, and for FCQs! 3

Last Time: Two-lens optical instruments Flea (Robert Hooke) Microscopes Telescopes Yerkes

Last Time: Hooke s two-lens microscope A magnifying glass (the eyepiece) magnifies the first image further. lens 2 image lens 1 image object lens 2 eyepiece lens 1 Nosepiece or Objective The first lens, the nosepiece, is used as a projection lens. 6

Last Time: Hooke s discoveries The cell Detailed structure of creatures. Example: The flea (plague). 7

Last Time: Galileo s telescope (~1600) Negative lens for eyepiece gives right-side-up image. BUT really terrible for the observer, must move eye around to see the full image. Poor field of view 8

Last time: Kepler s telescope (~1600) lens 1 image lens 2 image lens 2 eyepiece lens 1 Objective Positive lens for eyepiece gives upside down image. It s upside down, but brighter and is easier to see, great field of view. All telescopes are like this now. 9

Yerkes observatory, Largest refractor 40 inch lens 1897 Larger lenses sag too much under their own weight. The lens is achromatic (two kinds of glass). 12

Yerkes Today Still available for observations in the original observatory. Lake Geneva Wisc. COLD winters yield great seeing. Constant pressure from developers for the lakeshore. 40 inch main lens 13

Newton s telescope: Like Kepler s but with a mirror for the objective! Advantages: no chromatic aberration Advantages: Easy mirror support! All large telescopes use mirror objectives 14

Newton s reflector telescope 4 inch. 15

Palomar reflector - 5 meter mirror 16

Largest single mirrors are 8 m now Prof. Roger Angel s group. University of Arizona 17

Finished mirror (don t sneeze) 18

Keck Telescope 36 mirrors 10 m dia. 19

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 20

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 21

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 22

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 23

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 24

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 25

Magellan Telescope (yr. 2022) 24.5 m dia. segmented mirror 26

European Extremely Large Telescope (42 m dia.) would use many smaller mirrors 27

A telescope is used to look at distant objects. The objective lens produces an image of the object that is: A) Right-side up and virtual B) Right-side up and real C)Inverted and virtual D)Inverted and real E) Depends upon the object. 29

A telescope is used to look at distant objects. The objective lens produces an image of the object that is: A) Twice the focal length, f, from the objective B) Exactly f from the objective C) Slightly more than f from the objective D) Slightly less than f from the objective E) Cannot be predicted. HINT: 1/do + 1/di = 1/f and do is large, but not infinite! 30

Kepler s telescope, the objective Focal point Lens 1 image First image has the same Angular Size as the original object lens 1 Objective 31

Last time: Kepler s telescope (~1600) lens 1 image lens 2 image lens 2 eyepiece lens 1 Objective Eyepiece is a magnification glass, Let s you get closer and still be focused on retina SO image is larger on retina. Larger angular size. 32

Magnification of a telescope (refractor or reflector) Magnification = - focal length of objective lens or mirror focal length of eyepiece Example: Objective focal length = 1 m = 100 cm Eyepiece focal length = 1 cm Magnification = -100 33

Your parts go together to make a Keplerian telescope Do you recall the approximate focal lengths of the thin lens and fat lens? A) Thin: 3.5 cm Fat: 35 cm B) Thin: 1 meter Fat: 35 cm C) Thin: 35 cm Fat: 3.5 cm D) Something else. The magnification should be about: A) -1x B) -10x C) -100x D) -0.1x 34

Open for questions! 35

The remaining lectures: Ch. 5 (the eye), Ch. 6 (optical instruments), We are here Ch. 7 (Retina and visual perception), Ch. 9 & 10 (color & color perception). 36

Next topic: Depth perception Depth Perception: How do we see a 3D world with a 2D image? Parallax and binocular vision (We have two eyes!)

Parallax To gauge depth, you rely on the fact that the view is different from different positions of your head - parallax. This effect cannot be mimicked on a flat painting - as you move your head, objects that are behind other objects do not move by different amounts. e.g. the finger in the poster always points toward you, no matter where you head is. An actual finger would not. Try it: Look at your pencil (with one eye) straight on then move your eye and/or the pencil to the side Alfred Leete s 1914 recruiting poster of Lord Kitchener

Binocular disparity Human (predator) eyes are in front of our heads: 130 degrees of overlap. Good depth perception! But field of view just 208 degrees. Dog: overlap is 100 degrees. Rabbit (prey) field of view = 360 degrees! Only 24 degrees of overlap.

Binocular disparity Try it: First try out your field of view: close one eye then the other, what part of the scene overlaps? Focus on your thumb about 12 inches in front of you Then focus on a distant object (Light bulb) What do you see as you sequentially close one eye then the other? Close each eye sequentially how does what you see compare?

Visual Cues - Binocular Disparity Because the two eyes are separated by 6.5cm, we do not have to move our heads to get a perception of depth. The difference between the views of Your eye/brain system is the two eyes is called binocular disparity. constantly computing to get a full view of the world around However, we see a 3-dimensional you! world, not two 2-dimensional images! As before, binocular disparity also works best for close objects, because the eyes see almost the same for faraway objects. http://www.yorku.ca/eye/toc-sub.htm

Binocular Vision Now try looking at your thumb and the distant object again but now with both eyes open When you see two thumbs the image is falling on non-corresponding points on the left and right retina http://lifesci.rutgers.edu/~auerbach/bmlec10/sld024.htm

The brain How does our brain combine images from both eyes? Brain damage on the left side hurts vision on the right side!

Binocular disparity Try it: Focus on your thumb about 12 inches in front of you Then focus on distant object What do you see in each case? Close each eye sequentially how does what you see compare? Hold up two thumbs how far apart do you need to place them to always block the lightbulb as you close your eyes sequentially? Now open both eyes what do you see?

Binocular Vision the Frankfurter Illusion http://www.michaelbach.de/ot/sze_frankfurter/index.htm

Other unambiguous depth perception cues: Accommodation Depth perception: More cues

Other depth perception cues Shadows (Ambiguous cues) Shading on the left edges make these images look 3D

What do you see? A) Craters B) Mounds

We expect a 3D world, lit from ABOVE: Craters? light Mounds? light 50

Stop here for the FCQs colorado.campuslabs.com/courseeval using a phone, tablet or computer. Please give us your feedback. It is very helpful! 51

Good place for a break Enjoy your day! Project Progress Report feedback coming. Online and Written HW12 due next week. 52