VISUAL OPTICS MIDTERM PRACTICE QUESTIONS - January 2009

This is a compilation of test questions from several old tests and some new questions. The question distribution is not meant to be representative of the weighting of the actual test.

All questions are four-choice, multiple-choice questions. For each question select the letter on the answer sheet that corresponds to the most appropriate answer. Only one choice is correct for each question.

Q1.Low contrast fringes are produced in a Young’s double slit experimental setup. In which of the following cases will ALL of the listed modifications help to improve fringe contrast?

(A)reduce source bandwidth, increase (mean) source wavelength, move the double slit away from the source slit

(B)reduce source coherence time, increase (mean) source wavelength, move the slits in the double slit closer together

(C)increase source coherence length, decrease (mean) source wavelength, narrow the source slit

(D)increase source bandwidth, move the double slit away from the source slit, narrow the source slit

Q2.Monochromatic light waves ( = 500 nm) from a distant point source are incident on a 0.6 mm (diameter) circular aperture. Determine angular size of the resulting Airy Disc:

(A)0.058

(B)0.117

(D)0.233

Q3.The Rayleigh Criterion would most accurately predict the ability of a real, healthy, unoperated, eye to resolve two closely adjacent point sources for a pupil diameter of:

(A)1 mm

(B)2 mm

(D)8 mm

Q4.For light of wavelength 505 nm shone through a single slit, the first dark region on the screen image is located 2 cm from the center of the central maximum. If the screen is 10 meters away from the slit, what is the slit width?

(A)0.125 mm

(B)0.250 mm

(D)0.500 mm.

Q5.If longitudinal spherical aberration is 600 m in a particular optical system for an 8 mm aperture, then for a 2 mm aperture, it will be:

(A)9.4 m

(B)37.5 m

(D)125 m

Q6.

The three circles on the above figure (not drawn to scale) correspond to the largest comatic circle produced by a lens for an aperture diameter of 3 mm (smallest circle), 6 mm (medium circle) and 9 mm (largest circle). The same off-axis object point was imaged in each case. If the sagittal coma for the 3 mm aperture was 200 m, the sagittal coma for the 9 mm aperture would be:

(A)600 m

(B)1,800 m

(D)16,200 m.

Q7.For a +8.0 D spectacle lens, off-axis (oblique) astigmatism for central refraction and a 15 angle of obliquity would be:

(A)0.15 D

(B)0.57 D

(D)2.14 D.

Q8.The optimum thickness for an antireflection film is:

(A)Half the (vacuum) wavelength of incident light

(B)Half the wavelength of incident light as it travels through the film

(C)One quarter the (vacuum) wavelength of incident light

(D)One quarter the wavelength of incident light as it travels through the film.

Q9.Corneal asphericity in human eyes:

(A)is the cause of ocular spherical aberration

(B)varies from person to person, explaining why some people suffer greater visual acuity loss due to coma than others

(C)helps to reduce the amount of distortion in the retinal image of spectacle-wearing patients

(D)varies from person to person, explaining why some people suffer greater visual acuity loss due to spherical aberration than others.

Q10.Oblique astigmatism and curvature of field are the two most important aberrations to correct in ophthalmic lenses because:

(A)these are the only two aberrations over which we have any control in spectacle lens design

(B)of all the intrinsic ocular aberrations, these two are the most detrimental to retinal image quality

(C)these are the only two aberrations that cannot be corrected by wavefront-guided refractive surgery

(D)these two aberrations reduce retinal image quality as the eye rotates to look through more peripheral parts of the spectacle lens.

Q11.Loss of retinal image quality due to curvature of field is eliminated in a spectacle lens when:

(A)the Petzval surface matches the far point sphere

(B)the patient’s spectacle lens design is based producing a Petzval surface that matches retinal curvature

(C)the image surface of a plane object produced by the spectacle lens is place

(D)the image surface produced by the spectacle lens meets the Petzval condition.

Q12.

Young’s double slit experiment produces the above screen intensity profile (center of image indicated by arrow). There is a totally dark region about two thirds of the way from the center of the screen to each edge (arrows) What is the approximate relationship between slit width (each slit in the double slit) and slit separation?

(A)slit separation ~ twice slit width

(B)slit separation ~ five times slit width

(C)slit separation ~ ten times slit width

(D)slit separation ~ twenty times slit width.

Q13.Optical coherence tomography is a procedure that works because of low temporal coherence in the system. This low temporal coherence is produced by:

(A)Using very narrow “pinhole” apertures throughout the system

(B)Using a light source with very long coherence length

(C)Using a very wide source slit in front of the system light source

(D)Using a broad bandwidth light source.

Q14.Light of wavelength 525 nm is shone through a single slit of width 0.2 mm. The angle subtended by the first order diffraction minimum (measured from the center of the screen image is):

(A)0.150

(B)0.183

(D)0.367

Q15.For this question, assume that the eye is diffraction-limited Two closely adjacent point sources of wavelength 525 nm will just be resolved through a 1 mm pupil if they are separated by an angle of:

(A)0.030

(B)0.037

(D)0.074

Q16.The resolution of real eyes departs from the Rayleigh criterion at larger pupil diameters because:

(A)Airy discs become progressively wider with increasing pupil diameter and therefore spread over more photoreceptors

(B)Airy discs become progressively narrower with increasing pupil diameter and are therefore no longer separated by an unstimulated photoreceptor

(C)Aberrations become the limiting factor for resolution between a 1.3 mm and 3 mm pupil diameter. After 3 mm, resolution is limited by a combination of diffraction and aberration effects

(D)Aberrations degrade the retinal image more and more as pupil diameter increases beyond 1.3 mm up to the largest pupil diameter.

Q17.Scanning laser ophthalmoscopes and wavefront-correcting refractive surgery systems use a deformable mirror. The purpose of this deformable mirror is to:

(A)Measure and then neutralize the intrinsic wavefront aberration of the instrument’s optical system

(B)Determine the optimum pupil diameter for the patient to allow optimal resolution of the fundus (SLO) or optimum pupil diameter for post-surgical visual acuity

(C)Measure the wavefront aberration of the patient’s eye

(D)Neutralize the wavefront aberration of the patient’s eye to allow optimal resolution of the fundus (SLO) or optimum post-surgical visual acuity

Q18.A spherical lens is found to have +200 M longitudinal spherical aberration when the aperture in front of the lens is set to 3 mm. If the aperture is now opened up to 4 mm, longitudinal spherical aberration will be:

(A)250 M

(B)356 M

(D)600 M

Q19.

The above figure shows the image pattern produced by an off-axis object point that is imaged through a spherical lens. Each of the labeled dots (1-5) corresponds to the bottom of one of the five circles seen in the pattern. What do these five indicated locations signify?

(A)They correspond to the image points produced by light incident at five different aperture heights in the tangential plane

(B)They correspond to the image points produced by light incident at the margin of the lens in five different meridians (tangential, sagittal, and three oblique meridians)

(C)They correspond to the amount of transverse spherical aberration produced for five different aperture diameters

(D)They correspond to the image points produced by light incident at five different aperture heights in the sagittal plane

Q20.Real eyes do NOT typically have spherical corneas. The cornea flattens progressively from center to periphery in the average eye. As a result:

(A)The average eye has less longitudinal spherical aberration than would be predicted for an eye with spherical cornea but transverse spherical aberration matches the prediction for an eye with spherical cornea

(B)The average eye has the same longitudinal spherical aberration as would be predicted for an eye with spherical cornea, but less transverse spherical aberration

(C)The average eye has longitudinal and transverse spherical aberration that nicely matches what would be predicted for an eye with spherical cornea

(D)The average eye has less longitudinal and transverse spherical aberration than would be predicted for an eye with spherical cornea

Q21.For Young’s double slit experiment, interference fringes superimposed on a diffraction profile with visible minima and maxima are clearly seen on the image screen. The slit separation is now halved. How will the screen intensity profile change:

(A)The first order diffraction minimum on each side of the central diffraction maximum moves closer to the center of the screen

(B)The first order diffraction minimum on each side of the central diffraction maximum moves further away from the center of the screen

(C)The separation of adjacent interference maxima decreases across the screen and more interference maxima are visible per unit distance on the screen

(D)The separation of adjacent interference maxima increases across the screen and less interference maxima are visible per unit distance on the screen

Q22.Assume an eye is diffraction-limited. If two green point sources of light (550 nm) can just be resolved when they are separated by 1.15 arc (0.019) for a given pupil diameter, under what conditions will two red light sources (650 nm) separated by 1.15 arc be resolved by this eye:

(A)Only if the pupil is dilated sufficiently

(B)For the same pupil diameter, but no smaller

(C)For the same and some smaller pupil diameters

(D)Only if the pupil is constricted sufficiently

Q23.Assume that the eye is diffraction-limited for this question. Two monochromatic point sources separated by a very small distance are just resolvable by the eye with 4 mm pupil diameter. The pupil now constricts to 2 mm. Are the two points still resolvable, and why?

(A)No, because the Airy discs corresponding to the images are no longer separated by the radius of an Airy disc

(B)Yes, because the Airy discs corresponding to the images are now separated by a distance greater than the radius of an Airy disc

(C)No, because interference fringes in the image are further apart with the smaller pupil diameter

(D)Yes, because of the pinhole effect

Q24.For this question, assume that the eye is subject to all the real image-degrading effects that occur at various pupil diameters. For which of the following pupil diameters does the eye’s resolving ability show the greatest departure from the Rayleigh criterion?

(A)1.3 mm

(B)2 mm

(D)4 mm

Q25.For Young’s double slit experiment and light of wavelength 656 nm, two slits of width 0.2mm are separated by a distance of 0.5 mm. Determine the angle between the central interference maximum and the third order interference maximum:

(A)0.113

(B)0.226

(D)0.563

Q26.The purpose of the deformable mirror used in the scanning laser ophthalmoscope is to:

(A)measure the wavefront aberration of the patient’s eye

(B)measure the wavefront aberration of both the patient’s and practitioner’s eye

(C)compensate for the wavefront aberration of the patient’s eye

(D)compensate for the wavefront aberration of the instrument’s optical system

Q27.An optical system consists exclusively of spherical lenses and spherical surfaces. With the primary aperture in the system (aperture stop) set to 3 mm, transverse spherical aberration is measured to be 60 m. The aperture is now re-set to 6 mm. Determine the new value for transverse spherical aberration:

(A)120 m

(B)240 m

(D)960 m

Q28.For most real eyes, longitudinal and transverse spherical aberration (LSA and TSA) do not increase as rapidly with pupil diameter as would be predicted by the standard LSA and TSA equations. The primary reason is that:

(A)the eye is a physiological spherical system, not a series of lenses, so spherical aberration equations tend to give inaccurate measures of image degradation

(B)the reduced surface, while appropriately spherical, is steeper than the cornea of the eye it represents

(C)the LSA and TSA equations are not very accurate and tend to overestimate spherical aberration for spherical surfaces

(D)the cornea is not spherical, but actually aspheric in shape, curvature decreasing progressively from center to periphery

Q29.In Young’s double slit experiment, all of the following changes would increase spatial coherence, except:

(A)decreasing source slit width

(B)increasing separation of the slits in the double slit

(C)increasing mean source wavelength

(D)increasing distance between source slit and double slit

Q30.Longitudinal spherical aberration (LSA) through a positive spherical lens is found to be +100M for an 8 mm aperture diameter. The aperture diameter is now changed and the new value for LSA is measured as 12.5 M. What is the new aperture diameter?

(A)1.0 mm

(B)2.0 mm

(D)4.0 mm

Q31.A graph showing the experimentally determined resolution of the human eye as a function of pupil diameter demonstrates that:

(A)Aberrations exert their maximum image-degrading effect for a 1.3 mm pupil diameter

(B)Aberrations exert their maximum image-degrading effect for a 3 mm pupil diameter

(C)Aberrations exert their maximum image-degrading effect for the largest tested pupil diameter

(D)Aberrations exert a relatively constant effect across all measured pupil diameters because the Rayleigh criterion is responsible for the variation in resolution

Q32.Coma and oblique astigmatism exert the greatest image-degrading effect in the tangential plane because:

(A)this plane is defined by the direction of the off-axis object point

(B)lens surface curvature is greater in the tangential plane than in the sagittal plane

(C)the tangential plane is vertical and these aberrations exert their effects predominantly in the vertical direction

(D)this is perpendicular to the horizontal direction of incident light, thereby producing the greatest transverse image spread

Q33.The type of distortion that a 20 D spectacle-corrected hyperope would experience is:

(A)zero to negligible distortion

(B)barrel distortion

(C)pincushion distortion

(D)sagittal distortion

ANSWER KEY

1A21D

2B22A

3A23A

4B24D

5B25B

6B26C

7B27C

8D28D

9D29B

10D30C

11A31C

12C32A

13D33C

14A

15B

16D

17D

18B

19A

20D