• Notes & Hazards
• Corrections
• Helpful Links

Random helpful notes for your experiment:

1. Notes on the Theory part:
   • Go to The Physics Classroom for EXCELLENT notes on the eye, lenses, and all the associated mathematics. The following images are from there:
     
     
     
   • In the lens equation (1/f = 1/d_o + 1/d_i), remember that both f and d_i can be negative.
   • For a converging lens, image formation is as follows:
     
     
     Please note that the image is below the axis; hence, h_i is negative (see table below) but since the image is on the opposite side to the incoming light, d_i is positive.
   • For a diverging lens, image formation is as follows:
     
     
     Please note that the image is above the axis; hence, h_i is positive (see table below) but since the image is on the same side as the incoming light, d_i is negative.
     Note: A virtual image can't be measured directly (need a real image for that) and that's why we'll be using the combination lens method in Section 4.3.
   • Sign Conventions:
     

     Variable	Lenses		Mirrors
     	Positive	Negative	Positive	Negative
     Focal length f	converging (positive lens)	diverging (negative lens)	concave -->)	convex -->(
     Object distance d o	light side	opposite side	reflecting side	opposite side
     Image distance d i	opposite light (real image)	light side (virtual image)	reflecting side	opposite side
     Object and image heights h o , h i	above axis	below axis	above axis	below axis
     Magnification	upright	inverted	upright	inverted

     
     
   • Remember that magnification is m = h_i/h_o = -d_i/d_o. Please note the negative sign in the equation. A negative magnification means the image is inverted. This can happen because either h_i OR d_i can be negative.
   • The diopter is simply defined as the inverse of the focal length (in meters): 1 diopter = 1/f. Also, remember that the thicker the lens, the shorter the focal length and the higher the diopter rating.
   • Visual defects and their corrections:
     
     

     Defect	Cause	Correction
     Hyperopia/Hypermetropia (Far-sightedness)	f > retinal distance	Converging Lens (Fig. 1, below)
     Myopia (Near-sightedness)	f < retinal distance	Diverging Lens (Fig. 2, below)
     Astigmatism	non-spherical lens; deformed cornea	Cylindrical lens

     
     Note about astigmatism: Astigmatism is defined as when the off-axis points are blurred in the radial or tangential direciton, and focusing on can reduce one at the expense of the other, but cannot bring both into focus at the same time. But as far as the lab is concerned, just remember that astigmatism is when one pair of lines in Figure 6 is clear and the others are blurry.
     Figure 1.
     Figure 2.
     
     
2. Notes on the Procedure part:
   • First and foremost: make sure you get the equipment for Lab 8 and NOT lab 9 (the other section will be doing Lab 9 this week).
   • Section 4.1, p. 93, Step 1: fix the lamp at the zero position but leave the screen and lens mounts free to move and adjust.
   • Section 4.1, p. 93, Step 5: remember that the standard deviation is
     square root { [S_i(x_i - <x>)² ]/n-1 } where n-1 is used when you have a sample and n is used (instead of n-1) if you have the entire population (see HyperStat Online for more on standard deviationsand samples, populations, and biased estimates).
   • Section 4.2, p. 94: the screen should be placed much less than 1 meter for the thicker lens (the one with the shorter focal length).
   • Section 4.3, p. 95: Tape the 2 lenses together. Also, an alternative derivation of (EQ 6) is:

     
     	             fcf1
     	      f2 = ---------
     	            f1 - fc
     	      

   • Section 4.5, on p. 97: for Q. 4.5.3, you might need to swap the values of the circle and the plus sign for the other eye (alternatively, you can just flip the book over to do the other eye).
   • Miscellaneous notes: For the Cenco Eye part, the lens' powers (and polarity) are written on the handle. The handle does not indicate the axis of symmetry for the cylindrical lens!
3. Some good links:
   • Some really nice pictures of (and more info about) the eye are available at Psych 2E03 Study Guide.
   • Also, here's an interesting link that explains why the sky is blue and the clouds are white.
   • A link with nice pictures of the eye defects we'll be seeing today and explanations of the corrective surgery for each. Also, you might want to check out the Lens Tutorial for a great explanation of how the diaphragm (or pupil) helps reduce diffraction effects.

1. Section 4.1, on p. 93, please ignore steps 3 & 4 where it tells you to place the light shield in front of the lens. It's too hard to mount and essentially unnecessary.

Required Materials:

1. Laboratory Manual (SGM 407)
2. Laboratory Answer Book
3. Calculator with statistical functions

1. This lab is going to be long so make sure you read it through before coming in. The Cenco Eye part takes about an hour so if you can get the other stuff done in less than an hour, you'll be in good shape to get outta there by a decent hour.
2. I'll be doing 8th week updates this week, too.
3. Feedback on if you're finding these pages helpful (or not) is definitely good. So if you have any strong opinions, or, dare I say it, ideas on how to make this better, drop me a line! Also, if you have any thoughts on the midterm review, please feel free to drop me a line (it'll only help improve the final review).