Kirk Sade Posted March 3, 2008 Share Posted March 3, 2008 Hello, I'm shooting outside during the day with a 500asa Tung stock, I have a 85b correction and want to shoot it with a 45 degree angle...so to set my lightmeter's ISO, is this calculations correct? -2 stops comp for shutter, brings me down from 500 to 125 -2/3 stop (which I'm going to put as 1 full stop) for 85b which brings me down from 125 to 64 ISO Is 64 asa correct? thanks a bunch in advance... Link to comment Share on other sites More sharing options...
Saul Rodgar Posted March 4, 2008 Share Posted March 4, 2008 Hello,I'm shooting outside during the day with a 500asa Tung stock, I have a 85b correction and want to shoot it with a 45 degree angle...so to set my lightmeter's ISO, is this calculations correct? -2 stops comp for shutter, brings me down from 500 to 125 -2/3 stop (which I'm going to put as 1 full stop) for 85b which brings me down from 125 to 64 ISO Is 64 asa correct? thanks a bunch in advance... That sounds right . . . Link to comment Share on other sites More sharing options...
Premium Member Michael Nash Posted March 4, 2008 Premium Member Share Posted March 4, 2008 That sounds right . . . Yes. Link to comment Share on other sites More sharing options...
Premium Member Chris Keth Posted March 4, 2008 Premium Member Share Posted March 4, 2008 Absolutely correct. Why are you using a full stop as your 85B correction? Just to build in some healthy overexposure? Link to comment Share on other sites More sharing options...
Premium Member Michael Nash Posted March 4, 2008 Premium Member Share Posted March 4, 2008 85 "B" has bit more density than a straight 85, so one full stop compensation rounds up for safety. Link to comment Share on other sites More sharing options...
Ken Minehan Posted March 4, 2008 Share Posted March 4, 2008 i have never shot at any other shutter angle other than 180 deg, so i am interested in finding out the compensation when shooting at different shutter angles. when you shoot at: 90 deg is it 1 stop of compensation? 45 deg is 2 stops of compensation? is this right? regards ken minehan Link to comment Share on other sites More sharing options...
rohtash chandel Posted March 4, 2008 Share Posted March 4, 2008 i have never shot at any other shutter angle other than 180 deg, so i am interested in finding out the compensation when shooting at different shutter angles. when you shoot at: 90 deg is it 1 stop of compensation? 45 deg is 2 stops of compensation? is this right? regards ken minehan the best way to understand this is to understand exposure time exposure time can be calculated by dividing shutter opening with the product of 360 and fps you are shooting at thus exposure time= shutter opening/ 360 x1/ fps thus when you shoot with 180 shutter opening at 24fps you get exposure time = 180/360X1/24 =1/2x1/24 =1/48 so now when you close your shutter to have 90 degree opening you get exposure time = 90/360x1/24 = 1/4x1/24 = 1/96 which is half the time a frame gets at 180 degree so in oder to make it normal exposure, film would require double amount of light thn it requires with 180 degree opening 2x1/96=1/48 thus you need to give one stop compensation; as it doubles the amount of light reaching the film hope it helps Link to comment Share on other sites More sharing options...
Kirk Sade Posted March 4, 2008 Author Share Posted March 4, 2008 Absolutely correct. Why are you using a full stop as your 85B correction? Just to build in some healthy overexposure? That's correct. Link to comment Share on other sites More sharing options...
DJ Kast Posted March 12, 2008 Share Posted March 12, 2008 (edited) What is the corellation between Stop Compensation and ASA. By that I mean, you started with and ASA of 500 and knew that you needed to compensate 3 stops, how did you get to 64? Is it just 500 to 200 to 125 to 64? Thanks for the clarification. Edited March 12, 2008 by DJ Kast Link to comment Share on other sites More sharing options...
Premium Member Chris Keth Posted March 12, 2008 Premium Member Share Posted March 12, 2008 What is the corellation between Stop Compensation and ASA. By that I mean, you started with and ASA of 500 and knew that you needed to compensate 3 stops, how did you get to 64? Is it just 500 to 200 to 125 to 64? Thanks for the clarification. ASA (ISO; Exposure index - all the same numbers) go on a scale by one-third stops. Halving or doubling the ISO numbers is a change of one stop. So, to go 3 stops from 500 is 64. 500 -1 stop change> 250 -1 stop change-> 125 -1 stop change-> 64. Link to comment Share on other sites More sharing options...
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