rating the iso or opening up on the lens

[darryl walthall]

a cinematographer can over or under- expose a film stock in at least two different ways , correct ? He can over expose a particular film stock if he changes the asa/iso from say 800 to 400 or He can simply open up one stop on the lens from, lets say, a t4 to a t2.8 .

So whats the difference in the two techniques ? Will the film stock respond in the same manner, even though the process of over-exposing the film one stop is different ?

On the surface it appears that the easier way to over-expose a film stock would be to simply open up on the lens . That way you don't have to "calculate" while on the set and you could leave your mind free to focus on other things like compostion, lighting, movement or whatever.

Maybe there is no difference in the two techniques and I am just over thinking the situation . Can anyone clarify ?

[Phil Rhodes]

Hi,

 

Yes, you're overthinking the situation - you can overexpose by opening up a stop on what your meter is telling you, or you can tell the meter that the stock is half the speed that it is, and the meter will tell you to open up a stop!

 

Phil

[David Mullen ASC]

Makes no difference. Setting your meter to a lower ASA value in order to overexpose the film just takes the burden off from remembering to do it on every shot.