human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Brand, Product Name, Focal Length, 35mm EFL and equivalent aperture, Max. aperture
###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?
gpt
SELECT Brand FROM table WHERE Max. aperture = f /2.8 AND Focal Length = 30mm AND Product Name = sigma 30mm f2.8 dn