Michael Althaus Posted January 10, 2006 Share Posted January 10, 2006 Hi, How do you usually calculate the sensitivity to set if a filter cuts 1/x of a stop. I mean, if I have a 400 ASA film and a filter I use takes 1/3 of a stop then I know that I have to set the filmspeed to 320. The math for this would be: 200 x 2^(2/3), right? Isn't there an easier way to do calculate it? I hope you understand what I mean, sorry for my lack of English.... Regards, Michael Link to comment Share on other sites More sharing options...
Premium Member Stephen Williams Posted January 10, 2006 Premium Member Share Posted January 10, 2006 Hi,How do you usually calculate the sensitivity to set if a filter cuts 1/x of a stop. I mean, if I have a 400 ASA film and a filter I use takes 1/3 of a stop then I know that I have to set the filmspeed to 320. The math for this would be: 200 x 2^(2/3), right? Isn't there an easier way to do calculate it? I hope you understand what I mean, sorry for my lack of English.... Regards, Michael Hi, Keep things simple, take a reading then open by 1/3 stop! Stephen Link to comment Share on other sites More sharing options...
Premium Member Laurent Andrieux Posted January 10, 2006 Premium Member Share Posted January 10, 2006 I have a 400 ASA film and a filter I use takes 1/3 of a stop then I know that I have to set the filmspeed to 320. The math for this would be: 200 x 2^(2/3), right? Since your starting point is "what value is 1/3 of a stop under 400 ?", the logical way to calculate this would have been 400/2^(1/3) But it is also true to say that the correct result is 2/3 of stop over 200 ASA and therefore your calculus is good. Since you know that 2^(1/3) = 1.25, you can just remember the series : 100, 125, 160, 200 etc. and multiply these figures by whatever factor you like to get the values you're looking for. For instance : 200, 250, 320, 400 are also the values by 1/3 of a stop steps... Look at your light meter you will see the sensitivity values are in that order Link to comment Share on other sites More sharing options...
Danish Puthan Valiyandi Posted January 10, 2006 Share Posted January 10, 2006 Michael, look here http://en.wikipedia.org/wiki/Film_speed to get a list of the most common film speeds. Each step equals a 1/3 stop. Just learn the common steps as Laurent says and forget about calculating on set :-) Greets, Dan Link to comment Share on other sites More sharing options...
Premium Member Chris Keth Posted January 11, 2006 Premium Member Share Posted January 11, 2006 Michael, look here http://en.wikipedia.org/wiki/Film_speed to get a list of the most common film speeds. Each step equals a 1/3 stop. Just learn the common steps as Laurent says and forget about calculating on set :-) Greets, Dan It's easiest to just remember the sequence of film speeds (or apply the compensation in your meter as such, as many meters can do that) rather than calculating anything on set. Link to comment Share on other sites More sharing options...
JA Tadena Posted January 12, 2006 Share Posted January 12, 2006 Yes. I dont really think there is a need to calculate since you will never be on a set without a light meter. :) Link to comment Share on other sites More sharing options...
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