Question: What is the maximum aperture of the lens(es) with a focal length of 20mm?
SQL: SELECT "Max. aperture" FROM "2-18729407-6" WHERE "Focal Length" = '20mm';

Question: What is the 35mm EFL and the equivalent aperture of the lens(es) with a maximum aperture of f /2.5?
SQL: SELECT "35mm EFL and equivalent aperture" FROM "2-18729407-6" WHERE "Max. aperture" = 'f /2.5';

Question: What is the brand of the Sigma 30mm f2.8 DN, which has a maximum aperture of f /2.8 and a focal length of 30mm?
SQL: SELECT "Brand" FROM "2-18729407-6" WHERE "Max. aperture" = 'f /2.8' AND "Focal Length" = '30mm' AND "Product Name" = 'Sigma 30mm f2.8 DN';