Question

What is the tolerance on flatness for Type-A optical flats of sizes up to 100 mm?

(a) 0.05 cm

(b) 0.05 µm

(c) 0.05 mm

(d) 0.05 m

This question was addressed to me during an internship interview.

This interesting question is from Optical Flats in section Measurement by Light-Wave Interference of Engineering Metrology

Answer 1

The correct answer is (b) 0.05 µm

For explanation: Tolerance on flatness for Type-A opticals flats is 0.05 µm for grade optical flats of size upto 100 mm only. But for the size between 101 mm to 200 mm the tolerance should be 0.10 µm. For grade II, it is 0.01 µm for size upto 100 mm and 0.20 for 101-200 mm.