Cuesta College, San Luis Obispo, CA
Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
The following questions were asked on reading textbook chapters and previewing presentations on corrective optics and magnifiers.
Selected/edited responses are given below.
Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Based on the reading and the presentation I understood that depending on what type of vision defect a person may have, that will determine what type of lens will serve to correct their vision. People with myopia need diverging lenses to correct their vision whereas people with hyperopia need converging lenses."
"When you look through two lenses: If the first lens would have formed a real image past the second lens then the image becomes a virtual object for the second lends. If the first lens forms a real or virtual image before the second lens, then the image is a real object for the second lens. The image formed by the first lens serves as the object for the next lens. Angular magnification is a value of how much larger the angular size of something appears as seen through a magnifier."
"I best understand the process of accommodation. I know that it is when our eye changes to help focus on objects at different distances and that this ability can deteriorate with age."
Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"The ray tracings are still giving me a lot of trouble."
"The difference between optical power and focal length."
"I found the two-step model to be a bit confusing unless applied to the prescriptions. I would like to go over some other examples we may see using the two-step model."
In general, a converging lens will produce a virtual, upright image located __________ the original object.
closer than. ******* [7] at the same distance as. * [2] farther than. ****************** [18] (More than one the above choices.) *** [3] (Unsure/lost/guessing/help!) ***** [5]
In general, a diverging lens will produce a virtual, upright image located __________ the original object.
closer than. ******************** [20] at the same distance as. [0] farther than. ****** [6] (More than one the above choices.) ***** [5] (Unsure/lost/guessing/help!) **** [4]
Identify the type of lens used for these optics. (Only correct responses shown.)
Glasses/contacts to correct for myopia: diverging [77%]
Glasses/contacts to correct for hyperopia: converging [74%]
Glasses/contacts to correct for presbyopia: converging [40%]
Magnifying lenses: converging [69%]
State the units of optical power for lenses, and briefly describe the relationship between optical power and focal length.
"The units are called diopters and they are equal to the inverse of the focal length."
Explain the difference between the two types of magnification, m and M.
"M refers to the angular magnification, whereas m refers to the transverse magnification. The former is the ratio of the angular size using the instrument to the angular size with the unaided eye, while the latter is the ratio of the image size to the object size."
If an object is brought closer to your eye, its angular size will:
increase. ************************ [24] decrease. ***** [5] remain unchanged. ** [2] (Unsure/lost/guessing/help!) **** [4]
When a converging lens is used as a simple magnifier, the object is placed at a distance p = __________ in front of (to the left of) the lens.
+∞. **** [4] +25 cm (at your near point). *************** [15] +f (at the focal point of the lens). ************ [12] (Unsure/lost/guessing/help!) **** [4]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I was confused on this slide from the blog. The one where you can see through the glasses and then around it is blurry. Are the two lenses different but our eyes combine them to make one perfect image?" (The view through the two lenses are shifted probably because of perspective, but yes, there seems to be a slight difference in their optical power, to correct for slightly different vision defects in each eye. Ideally your brain should integrate them together into a single view, but failing that, it may just concentrate on the dominant and/or more corrected eye.)
"The dolls performing optometry tests creeped me out."
"I'LL BE HONEST, I HAVE TWO MIDTERMS TOMORROW AND THURSDAY. I SORRY. ANY POINTS ARE BETTER THAN GETTING A ZERO. :(" (Two midterms this early in the semester--what's up with that? Anyway, good luck with those. Seriously.)
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