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Re: [Phys-l] Feynman's messenger lectures now available



Philip!

Evidently, they must do this (your below) before they can usefully use the matrix method. Its beauty is one may specify any (with in the paraxial approx. for the non-exact method) input vector and obtain the out put vector. The vector being the angle and height of incidence WRT the optical axis of the pencil. Not incidentally, students are now rather computer lit., so good exercise there.

--------------------
[Part I: Light Rays and Imaging:
Obtain an image using an object (use the old lamp housing with the crossed arrows), lens and
screen.
Use a card to block the object. In particular, slowly slide the opaque card across the face of the object. Watch the image. It should do exactly what you expect.
Now use the card to block the lens. Keeping the card very close to the face of the lens, slowly slide the card around while watching the image. Questions 1: Is this what you expected? What happened to the image as the card blocked the lens? How much of the lens had to be unblocked for an image to form? Did it matter what part of the lens was unblocked?
Next, take just a few minutes to explore the effect of the size of the opening. Set the opening of the iris so that it is a few millimeters across at most. Repeat what you just did with the card, that is, move the small opening around in front of the object and up close to the lens while watching the image. Try a few different sizes for the opening of the iris.]

Questions 1: Is this what you expected? What happened to the image as the card blocked the lens? How much of the lens had to be unblocked for an image to form? Did it matter what part of the lens was unblocked?
Next, take just a few minutes to explore the effect of the size of the opening. Set the opening of the iris so that it is a few millimeters across at most. Repeat what you just did with the card, that is, move the small opening around in front of the object and up close to the lens while watching the image. Try a few different sizes for the opening of the iris.

© 2009, John E. Sohl Page 1 of 4 PHYS 3190, Multiple Lenses

Think about question 2 before you do the next experimental step. Question 2: What do you think will happen if you take a broken piece of lens and try to image an object?
You have a lens that has been cut in pieces with a diamond saw. (The cut edges have been painted black to reduce light scatter from the rough glass.) Question 3: The results you just obtained with the card, iris and lens shard were probably surprising. Using the concept of rays (a drawing or two might help) explain how this works. Especially, explain how an image is formed with most of the lens blocked or even missing.


Question 3: The results you just obtained with the card, iris and lens shard were probably surprising. Using the concept of rays (a drawing or two might help) explain how this works. Especially, explain how an image is formed with most of the lens blocked or even missing.



http://planet.weber.edu/Optics/Handouts/Lab4-MultipleLenses.pdf


Note that John's lab. address all the questions and comments on this part of the thread.

bc forever a Googler.

On 2010, May 25, , at 14:04, Philip Keller wrote:

Yes, the books cover ray tracing. But often, students focus so much on what happens to the three or four rays that they have rules for that they think that those are the only rays there are! I like to have them draw those rays in one color, but then as an exercise, add in a bunch of other rays that you can draw after you know where the image is. This is a necessary trick if you are going to use ray tracing to locate the image formed by a "virtual object" in two lens systems.