LAB FOR SHADOW AND PROJECTION MOIRE -- 2/26/97

Figure 1. Shadow moire of bottle with coarse grid. Pitch = 0.227 cm. Angle between viewing direction and illumination direction is 20 degrees. Maximum physical diameter of bottle is 7.25 cm

Figure 2. Shadow moire of bottle with fine grid. Pitch is 0.111 cm. Off-axis illumination angle is 20 degrees.

Figure 3. Projection moire of bottle with reference plane pitch of 0.181 cm. Offset angle of illumination is 20 degrees.

Figure 4. Projection moire of vase with reference plane pitch of 0.181 cm. Off-axis angle of illumination is 20 degrees. The maximum physical diameter of the vase body is 4.46 cm.

1. Assuming the cross-section of the bottle is circular, what is the diameter of the upper part of the bottle as measured from the moire in Figure 1. What is the diameter of the necked region? Does this agree with the directly measured diameters? How do you take care of scaling?
   
2. Make the same measurements using Figure 2. What is the difference between the two images?
   
3. Make the same measurements using Figure 3. Do you get the same answers for the two methods?
   
4. How accurate do you think your measurements are for Figure 1 and Figure 2 ?
   
5. How deep is the neck built into the lower part of the bottle ? Does this agree with your direct measurement after scaling is taken into account?
   
6. Plot a horizontal line profile of depth variation across the middle or widest part of the vase in Figure 4.. How accurate are your results? How would you improve your accuracy? What is the limit on the accuracy you can hope to obtain?
   
7. Draw sketches and explain why the scaling factor for shadow moire is tan a, while for projection moire it is sin a.
   
8. Would increasing or decreasing the angle between viewing direction and light direction change the sensitivity of the reading? If so, which way for which method? No effect on either method?