BHS 120.2- Optics II
Notetaker: Niloufar Masheli
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Date: 01/29/2013, 1st hour
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As you know, the mediasite is down. Since we have an optics exam on Friday, I wanted
to get these notes to you ASAP. So, they are basically my own notes typed up. If anyone
finds an error, please let me know.
Dr. Saeed went over the answers to the 4 cases. These cases can be found under
Resources  Practice Problems  Magnification worksheet w/ answers
Dr. Saeed also went over 2 sample questions (not in our lecture packet) related to TS and
patients with uncorrected refractive errors. Those questions (w/ answers) have also been
posted under Resources  Supplementary Materials  Magnification III
The clicker questions are also on the Magnification III handout
Use of Telescope for near telemicroscope (Pg.10):
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L2’= L2 + P2 = +22.5 – 30= -7.48 D
With the TS, the vergence is -7.48 D (this is the
amplitude of vergence). The telescope adds to
the incoming divergence from the real object and
thus makes it difficult to see near objects.
Pg. 11:
- The lens cap is the reading cap. The reading cap is put in FRONT of the telescope.
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** Clinical application/importance of the reading cap: the Low Vision lanes at the IEI are
shorter than the standard 20 feet examination lanes. Therefore, the ideal ‘optical infinity’
is not achieved and we would have diverging light (from the eye chart) entering the
patient’s eyes (instead of the ideal parallel rays). In order to neutralize this divergence,
we could ‘dip’ a +ve lens in FRONT of the patient’s telescope (which would be mounted
on patient’s glasses) to take away from the divergence and to allow ‘parallel’ to exit from
the telescope. This +ve lens that is dipped in front of the telescope is called the reading
cap. The dioptric power of the reading cap depends on the incoming vergence from the
eye chart, which in turn depends on the eye chart’s distance from the patient. For
example, if the eye chart is 100 cm from the patient’s eyes, then its vergence would be 1.00 D. Thus, we’d need a +1.00 D reading cap to allow parallel rays to exit from the
telescope and hit the patient’s eyes.
Take home points, Pg. 11:
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M angular = - Pe ocular/ Pe objective  In both Keplerian and Galilean TS, the Pe ocular
is always stronger that the Pe objective. This goes back to the basic set-up of the two
telescopes  the ocular lens in the Keplerian TS is always the stronger convergent lens
BHS 120.2- Optics II
Notetaker: Niloufar Masheli
Date: 01/29/2013, 1st hour
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compared to its less-convergent objective lens. The ocular lens in the Galilean TS is
always the stronger divergent lens compared to its less-convergent objective lens.
**Thus, the M ang is always a ratio greater than 1 because the numerator
(compared to the denominator) is always the bigger number.
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An uncorrected myope will shorten the tube length d to create negative power in a TS
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An uncorrected hyperope will increase the tube length d to create +ve power in a TS.
Discard Information on pages 12-15 (inclusive)
Telescope in Afocal Setting, Pg. 16:
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In an afocal setting, parallel rays must enter and exit the telescope. We are going to
start with:
P objective = +8.00 D
L= 0.00 D
L’ = L +P = 0.00 + 8.00 = +8.00 D
f’ obj = 1/ +8.00= + 12.5 cm (f’ object is measured from the objective lens)
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Now, based on P ocular= -40.00 D, we know:
L ocular = +40.00 D
L’= L ocular + P ocular = +40.00 – 40.00= 0.00 D
f ocular= - (1/-40.00 D) = +2.50 cm
d= 10 cm
Use of telescope by an uncorrected 5.09 D myope changing the tube length to d’, Pg. 16:
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A myope has too much focusing power (i.e. an emmetrope has +60.00 D of focusing
power and the myope in this example has +65.09 D of focusing power  image is
formed in front of retina. Therefore, we need the rays that exit the P ocular to provide us
with -5.09 D of divergence. Since the P ocular= - 40.00 D, then the rays that enter the P
ocular must have relatively decreased convergence to allow diverging rays to exit the P
ocular. Therefore:
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L ocular= +34.91 D
L’ ocular= L+ P= +34.91 – 40.00= -5.09 D
l ocular = 1/L ocular = 1/ +34.91 D= +2.86 cm
f’ obj= 1/+8.00 = +12.5 cm
d’= 9.64 cm
g= d’- d = 9.64 – 10= -0.36 cm (the –ve ‘g’ value tells us that the tube length has been
decreased)  (Note: the fact that we see d’ (as opposed to d) hints to the fact that the
patient is adjusting the tube length to account for their refractive error.)
BHS 120.2- Optics II
Notetaker: Niloufar Masheli
Date: 01/29/2013, 1st hour
Page3
Use of telescope by an uncorrected 5.78 D hyperope changing the tube length to d’, Pg. 19:
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Hyperopes’s focusing power is relatively weak (i.e. an emmetrope has +60.00 D of
focusing power, whereas the hyperope in this example has +54.22 D of focusing power).
Thus, we need convergent rays to exit from the P ocular and strike the patient’s eyes.
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Since P ocular is set to -40.00 D, then in order to get more convergence exiting the P
ocular, we need more convergent to enter it. Therefore:
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L ocular= +45.78 D
L’ocular= L +P = +45.78 – 40.00 = +5.78 D
l ocular= 1/ L ocular = 1/ +45.78 = +2.18 cm
f’ obj= 1/+8.00 = +12.5 cm
d’= 10.32 cm
g= +0.32 cm (the +ve ‘g’ value tells us that the tube length has increased)