Zeiss Optical Internal Measuring Device for Universal Measuring Microscope UMM
For this method of measuring a crossed slit projector is used which produces the image of a crossed slit in the measuring plane, where it is observed with the instrument microscope. The slits are adjusted to lie exactly on the optical axis of the microscope. The test piece lies between the projector and microscope and the projected cross-slits are reflected from the measuring surface. Only if the measuring face lies in the optical axis of the microscope will the projected slits appear as one set (otherwise the double prism produces counter moving double slit crosses in complementary colors). In this position the value on the cross and longitudinal scales is read. When measuring holes one of the slit appears curved. In this case the complementary images are set for symmetry. With this method it is possible to measure unusually deep and small holes, as well as tapered parts, with great accuracy. The equipment is used particularly for evaluating snap and ring gauges. Note that this accessory can only be used with an 8x objective.