Accuracy in measuring the dimensions of components by the shadow projection method

Conclusions

• 1. The measurements of cylindrical and threaded articles by means of a microscope and a shadow-projection method depend not only on the diameter of the illuminator's aperture but also on the position of this aperture's center.

• 2. A decentering of the aperture produces errors with a positive sign. The physiological errors which are usually measured in reference books and operating instructions are small as compared with the decentering error.

• 3. The empirical formulas and tables suggested by several authors are only applicable to those microscopes which were used for these experiments. The application of these tables to all instruments may lead to considerable errrors.

• 4. When the aperture is correctly centered, the error due to the article's contour distortion can be determined from the simple formula

  $$x = - \frac{{rU^2 }}{6}$$

  . In this instance the shadow-projection method of measurement becomes more accurate than that with blade probes.

• 5. New microscopes should be designed in such a manner as to eliminate the undesirable effect of the light reflected from the article which has a curvature along the optical axis of the microscope.

• 6. The Committee's instructions for testing instrument and universal microscopes should include the requirement for centering the illuminator.