This lens goes to up to f/1.8. There's a better version of it that goes to f/1.4. Every lens has it's set limits on how high or low you can set the f-number. My kit lens is f/4.0-5.6, depending if I zoom in or out, which I think is pretty average, 'cause my 2 telephoto lenses are the same. Look at the details written on the lens, it'll tell you what aperture it can achieve, as well as some other simple things, like the minimum distance it'll work best at.