Cuesta College, San Luis Obispo, CA
Students have a bi-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.
"Ray tracings are accurate models of how light passes through a lens to create an altered image of the object. The way that the three rays interact with the lens and the focal points determine if the image of the object is: upright or inverted and magnified or diminished."
"The refractive power of contact lens is expressed as the inverse of the focal length. To correct shortsightedness, a diverging lens is prescribed, and for hyperopia, a converging lens is used. The angular magnification measures the angular enlargement or reduction of an object through a lens."
"So basically the two-lens method consists of just getting an image from one lens and then using that image as the next object and thus get another image through the second lens. Which happens with any corrections to your eyesight such as contacts or glasses. I just learned why prescriptions have either the ± sign in front, I can describe how happy I am that I know this now."
"That glasses or contacts over eyes means the light is going through two lenses, the eyes and the contacts. I understood that angular size is not the actual size but the size it relates to the eye from your viewpoint."
"Magnifying glasses do not actually magnify, instead they 'bring' the object closer to the eye. Magnifying glasses allow the eyes to focus on an object when it is closer than 25 cm, the normal point of vision."
"I feel like angular magnification is more intuitive than linear magnification. The angular size of an object is not it's actual size, but it is how large the object appears to be on the retina. This size is given by the angle at which light from the object enters the lens. This is why huge object appear small if they are far away. The far distance creates a small angle."
"The best way to approach optics is to take them one lens at a time. An object goes through one lens to produce an image and then that image is the new object for the second lens. Angular magnification is the way magnifiers work, which allow you to see the object at a greater angular size. This image appears closer and is able to keep the clarity."
"I promise I will read about it this weekend."
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.
"I still have trouble applying ray tracings to examples. I think I just have to keep practicing and applying it to things to understand as time goes on."
"I found how optometrists make prescriptions confusing as well as how contacts/glasses actually work when you look at the numbers."
"How the two-lens setup corrects for myopia and hyperopia. I know that the contacts take the object and create an image that the eye is able to see, but I do not understand how the parameters change (focal points and image distance)."
"I don't understand how diopters work, and how the concept of refractive power factors in. I am also a little confused on converging and diverging lenses."
"I am still confused by magnifiers and how they actually work with a relaxed human eye closer or further away from the near focal point of +25 cm. how does this concept compare or relate to the ray tracings?"
"I found everything from the two-lens systems confusing. I don't even know enough to explain what I do or don't know."
"I'm sure you'll go over it in lecture but I could use a bit more explanation on the angular magnification equation."
"Utilizing the equations in problems like homework has also been confusing."
"It would be really helpful if you go over how magnifiers work and what it means when it says focused at infinity."
In general, a converging lens will produce virtual, upright images located __________ the original object.
closer than. **** [4] at the same distance as. ** [2] farther than. ********************** [22] (Unsure/lost/guessing/help!) ***** [5]
In general, a diverging lens will produce virtual, upright images located __________ the original object.
closer than. ************************** [26] at the same distance as. * [1] farther than. * [1] (Unsure/lost/guessing/help!) ***** [5]
Identify the type of lens used for these optics. (Only correct responses shown.)
Glasses/contacts to correct for myopia: diverging [58%]
Glasses/contacts to correct for hyperopia: converging [64%]
Glasses/contacts to correct for presbyopia: converging [33%]
Magnifying lenses: converging [61%]
State the units of refractive power for lenses, and briefly describe the relationship between refractive power P and focal length f.
"m–1. Refractive power is used to tell the focal length of contact lenses and is the inverse of focal length."
"Diopters. P = 1/f."
"I really don't know...I need help."
Explain the difference between the two types of magnification, m and M.
"Magnification (m) is the ratio of image height to object height and magnification (M) denotes how much larger the angular size of something appears as seen through a magnifier."
"Lower case m is the linear magnification which is the ratio of image length to object length. Capital M magnification is the angular magnification and denotes how much larger the angular size of something appears through a magnifier vs the naked eye."
A nominal, relaxed eye is set to focus on objects located at:
+∞. ****** [6] +25 cm (at your near point). ************** [14] +f (at the focal point of the lens). ******* [7] (Unsure/lost/guessing/help!) ****** [6]
If an object is brought closer to your eye, its angular size will:
increase. ******************* [24] decrease. * [1] remain unchanged. *** [3] (Unsure/lost/guessing/help!) ***** [5]
When a converging lens is used as a simple magnifier, the object is placed at a distance do = __________ in front of (to the left of) the lens.
+∞. ***** [5] +25 cm (at your near point). ***** [5] +f (at the focal point of the lens). ************** [14] (Unsure/lost/guessing/help!) ********* [9]
The ray tracing that best matches when a converging lens is used as a simple magnifier is:
#3. ******** [8] #4. ************** [14] (Unsure/lost/guessing/help!) *********** [11]
Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"I think more ray tracing in lecture would be helpful. I'm starting to get it, but there's still some doubt."
"This material is harder to understand so hopefully class will clarify my confusion."
"I'm sorry! I have a calculus test and a chemistry test and I need to study really bad :/ "
"Favorite anime?" (Recent favorites? Kill la Kill, Arpeggio of Blue Steel, FLCL (the original series). If you want to get old school, then The Super Dimension Fortress Macross, Space Battleship Yamato, Space Pirate Captain Harlock.) "
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