| 摘要 |
PROBLEM TO BE SOLVED: To provide a density filter having a gradation part which varies linearly in transmissivity. SOLUTION: The density filter is inserted into an aligner between its 1st lighting optical system and 2nd lighting optical system, which protect the illumination light emitted by a light source on an original plate, where a specific pattern is formed and the gradation part has repeated patterns of light shield patterns 402 and light transmission patterns 401 arrayed and formed with intervals P, which meets two conditions represented by P<=λ/(NA1+NA2) (NA1: density filter side numerical aperture of 1st lighting optical system, NA2: density filter side numerical aperture of 2nd lighting optical system,λ: wavelength of illumination light) andΔ/αP2=Si2-Si+12 (Δ: light intensity difference on original plate corresponding to arbitrary (i)-th (i: natural number) light transmission pattern and (i+1)-th light transmission pattern, Si: arbitrary (i)-th light transmission pattern area,α: constant).
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