The first question to ask oneself when you are looking to purchase a quality lens for film making purposes is what exactly are you shooting? Will your film be primarily of large open landscapes, close ups of people’s faces, action scenes or a combination of them all? Some lenses will allow you to frame many different scenarios with just one lens… but others, say close ups of extremely small objects … such as if you were doing a documentary on a certain breed of insect… might require a special lens to accommodate smaller subject matters in such intimate detail. The second question to ask is what is the mood of your film? In other words, what kind of film and lighting will you be using. A film dedicated to the dark realms of say, film noir will require lenses that can open up and capture what you are looking for in extremely low light settings. Or will you be shooting primarily outdoors in the day time where light is in much abundance. Will the lighting be artificial or natural, is the film color or black and white? All of these answers will point you in the direction of finding the correct lens or combination thereof to meet all of your film making needs.