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#1
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Adam's Exposure Formula contracts with the Addative Photographic Exposure System (APEX)
in Adams's book 'Negative', page 66, he showed a Exposure Formula:
" to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root. This number is remembered as the key stop for that firm. for example, a film rated as ASA 125 has a key stop of f/11. at the key stop, the correct shutter speed in seconds to expose a given luminace on Zone V is the reciprocal of the luminace expressed in c/ft^2. thus for a sureface that measure 60c/ft^2, we would use a shutter speed of 1/60 second at the key stop." but if using the APEX ( any one heard that? ), since Av + Tv = Bv + Sv, where Sv ( 125 ASA ) = 5.4, Bv ( 60c/ft^2 ) = 3.3, Av ( f/11 ) = 7, so Tv = 5.4 + 3.3 - 7 = 1.7 which is about 1/4 second. what's the wrong? thanks. - woody |
#2
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Adam's Exposure Formula contracts with the Addative PhotographicExposure System (APEX)
Steven Woody wrote:
in Adams's book 'Negative', page 66, he showed a Exposure Formula: " to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root [... see post ...} It is more clear if you graph it out but it is still unnecessary to go to lengths to understand it. It is an approach and not the ultimate method. Adams still dodged, burned and bleached his way to happiness. Learn to expose for significant shadows, develop for highlights and be happy. |
#3
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Adam's Exposure Formula contracts with the Addative Photographic Exposure System (APEX)
In article , JJ
wrote: Steven Woody wrote: in Adams's book 'Negative', page 66, he showed a Exposure Formula: " to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root [... see post ...} It is more clear if you graph it out but it is still unnecessary to go to lengths to understand it. It is an approach and not the ultimate method. Adams still dodged, burned and bleached his way to happiness. Learn to expose for significant shadows, develop for highlights and be happy. & use a light meter. -- George W. Bush is the President Quayle we never had. |
#4
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Adam's Exposure Formula contracts with the Addative Photographic Exposure System (APEX)
Gregory Blank wrote: In article , JJ wrote: Steven Woody wrote: in Adams's book 'Negative', page 66, he showed a Exposure Formula: " to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root [... see post ...} It is more clear if you graph it out but it is still unnecessary to go to lengths to understand it. It is an approach and not the ultimate method. Adams still dodged, burned and bleached his way to happiness. Learn to expose for significant shadows, develop for highlights and be happy. i just wonder, in this exposure, which one is wrong, Adams or APEX ? - woody |
#5
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Adam's Exposure Formula contracts with the Addative Photographic Exposure System (APEX)
Steven Woody wrote:
in Adams's book 'Negative', page 66, he showed a Exposure Formula: " to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root. This number is remembered as the key stop for that firm. for example, a film rated as ASA 125 has a key stop of f/11. at the key stop, the correct shutter speed in seconds to expose a given luminace on Zone V is the reciprocal of the luminace expressed in c/ft^2. thus for a sureface that measure 60c/ft^2, we would use a shutter speed of 1/60 second at the key stop." but if using the APEX ( any one heard that? ), since Av + Tv = Bv + Sv, where Sv ( 125 ASA ) = 5.4, Bv ( 60c/ft^2 ) = 3.3, Av ( f/11 ) = 7, so Tv = 5.4 + 3.3 - 7 = 1.7 which is about 1/4 second. 60 candles per square foot is a brightness level of around 7.5 That brings your total to 5.9 or very nearly 1/60th of a second. I think you looked up an incorrect table for brighness. In the Focal enclclopedia a bv of 7 is 45 canles/ ft^2 and a Bv of 8 is 90 candles/ft^2. Peter. -- |
#6
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Adam's Exposure Formula contracts with the Addative PhotographicExposure System (APEX)
Gregory Blank wrote:
In article , JJ wrote: Steven Woody wrote: in Adams's book 'Negative', page 66, he showed a Exposure Formula: " to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root [... see post ...} It is more clear if you graph it out but it is still unnecessary to go to lengths to understand it. It is an approach and not the ultimate method. Adams still dodged, burned and bleached his way to happiness. Learn to expose for significant shadows, develop for highlights and be happy. & use a light meter. Uh, yeah, and a lightmeter. and World Peace! |
#7
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Adam's Exposure Formula contracts with the Addative Photographic Exposure System (APEX)
Peter Irwin wrote: Steven Woody wrote: in Adams's book 'Negative', page 66, he showed a Exposure Formula: " to use the exposure formula, take the film speed number ( on the ASA scale ) and determine its approximate square root. This number is remembered as the key stop for that firm. for example, a film rated as ASA 125 has a key stop of f/11. at the key stop, the correct shutter speed in seconds to expose a given luminace on Zone V is the reciprocal of the luminace expressed in c/ft^2. thus for a sureface that measure 60c/ft^2, we would use a shutter speed of 1/60 second at the key stop." but if using the APEX ( any one heard that? ), since Av + Tv = Bv + Sv, where Sv ( 125 ASA ) = 5.4, Bv ( 60c/ft^2 ) = 3.3, Av ( f/11 ) = 7, so Tv = 5.4 + 3.3 - 7 = 1.7 which is about 1/4 second. 60 candles per square foot is a brightness level of around 7.5 That brings your total to 5.9 or very nearly 1/60th of a second. I think you looked up an incorrect table for brighness. In the Focal enclclopedia a bv of 7 is 45 canles/ ft^2 and a Bv of 8 is 90 candles/ft^2. Peter. -- thank you. after read you post and did a research on the net, i can now draw a conclusion that, 1, what adam mentioned 60c/ft^2 is a brightness of the scene. 60c/ft^2 brightness equals to a Bv value of 7.56 ( you are right ). 2, what i previously methioned Bv=3.3 for 60/ft^2 is from a table that actually list incident light values, which should be Iv instead of Bv. thank you very much!. - woody |
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