Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 75,270   Posts: 1,660,709   Online: 1079
      
Page 7 of 9 FirstFirst 123456789 LastLast
Results 61 to 70 of 81
  1. #61
    kintatsu's Avatar
    Join Date
    May 2012
    Location
    Bavaria, Germany
    Shooter
    4x5 Format
    Posts
    368
    Images
    2
    Quote Originally Posted by Alan Klein View Post
    Kintatsu: I believe you're correct. I recall reading about the 12% vs the 18%. But of course, that begs the question. If the meters are set for 12% standard, of what value is using an 18% gray card? Shouldn't we be using a 12% gray card so our reflective and incident readings will match? Does anyone make such a thing?
    I'm not sure if anyone makes one, but it would make sense.

    I remember reading. though, and forgot to mention, that not only is there a K factor, but also a C factor and what value the manufacturer uses seems to be up to them. I believe the 18% gray came from old print/publishing. If I recall correctly, the reason Ansel Adams and others pushed for 18% had to do with being able to print their negatives and have them published at the correct levels.

    You may want to check a printing house for a 12% card. I just test using my meter and go with that. I've found with my Starlite 2, I get box speed for FP4+. The difference between 12% and 18% is about 2/3 stop, I think. I'm sure your meter can be checked by shooting 2 shots of the same gray card 2/3 stop apart and printing it out. I never tried it, so it's just a theory.

  2. #62
    benjiboy's Avatar
    Join Date
    Apr 2005
    Location
    U.K.
    Shooter
    Multi Format
    Posts
    7,884
    To interpret light yes, to judge light intensity no, because the human eye reacts to quickly to changing light intensity for the brain to register it accurately , that's why light meters were invented, you take the meter reading first then interpret it with your knowledge and experience before setting the exposure .
    Ben

  3. #63
    Vaughn's Avatar
    Join Date
    Dec 2006
    Location
    Humboldt Co.
    Shooter
    8x10 Format
    Posts
    4,925
    Images
    40
    Quote Originally Posted by benjiboy View Post
    To interpret light yes, to judge light intensity no, because the human eye reacts too quickly to changing light intensity for the brain to register it accurately....
    This is why I recommend to our students not to look at their prints just as they walk out of the darkroom, and instead wait several seconds for their eyes to adjust to the light. If a student looks at his/her print as they exit the darkroom, their pupils are still dialated and that first impression is made. They then tend to add a little more time as the prints will seem a little light -- even though their eyes adjust and they continue to look at the print. Sort of a psychological dry-down effect.
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  4. #64

    Join Date
    Nov 2005
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    5,837
    Quote Originally Posted by kintatsu View Post
    ... not only is there a K factor, but also a C factor and what value the manufacturer uses seems to be up to them. ...
    K factor is for reflected light.

    C factor is for incident light.

  5. #65
    kintatsu's Avatar
    Join Date
    May 2012
    Location
    Bavaria, Germany
    Shooter
    4x5 Format
    Posts
    368
    Images
    2
    Quote Originally Posted by BrianShaw View Post
    K factor is for reflected light.

    C factor is for incident light.
    But they are calibrated to produce the same 12-18% depending on manufacturer, which leads to different readings on the meter, and between manufacturers.

    Gossen uses K=11.37, so if C=250 for a flat diffusor, we end up with a reflected gray value of about 14.3%. Other values for C exist for hemisphere diffusor, 320 is common. So using C=320, k=11.37, gray= 11.36%. The reflected percentage formaula is % reflectance for grey= pi(3.1416) x k/c. It would seem to me, that both numbers are factored to get the final reflectance value, and are dependant on each other and other mathematical gymnastics.

  6. #66

    Join Date
    Nov 2005
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    5,837
    Quote Originally Posted by kintatsu View Post
    But they are calibrated to produce the same 12-18% depending on manufacturer, which leads to different readings on the meter, and between manufacturers.

    Gossen uses K=11.37, so if C=250 for a flat diffusor, we end up with a reflected gray value of about 14.3%. Other values for C exist for hemisphere diffusor, 320 is common. So using C=320, k=11.37, gray= 11.36%. The reflected percentage formaula is % reflectance for grey= pi(3.1416) x k/c.
    That is my understanding too. I wish I understood more about the designer INTENT of the engineering values they use in their design models.

    No matter, I really believe that Bill Burk's bottom line (post #57) is correct. The design intent was for a photographer to be able to meter, use the provided exposure recommendation, and have a reasonably successful exposure MOST OF THE TIME. Knowing when that will and won't work is the difference between a good photographer and a photographer who is risking failure.

  7. #67
    kintatsu's Avatar
    Join Date
    May 2012
    Location
    Bavaria, Germany
    Shooter
    4x5 Format
    Posts
    368
    Images
    2
    Quote Originally Posted by BrianShaw View Post
    That is my understanding too. I wish I understood more about the designer INTENT of the engineering values they use in their design models.

    No matter, I really believe that Bill Burk's bottom line (post #57) is correct. The design intent was for a photographer to be able to meter, use the provided exposure recommendation, and have a reasonably successful exposure MOST OF THE TIME. Knowing when that will and won't work is the difference between a good photographer and a photographer who is risking failure.
    That about sums it all up. I would add that that's precisely why we do testing with our gear and our film. It gives us the knowledge to get repeatable results without the randomness of these factors.

  8. #68
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    4,088
    Images
    51
    Quote Originally Posted by Alan Klein View Post
    The answer can't be read the palm of your hand. What if you're black?
    What if the most reasonable answer IS to read the palm of your hand? I'm not a person of color, but I believe human palms are universally Zone VI.

    Same can't be said of the 18% gray card. It's not necessarily Zone V, and if you treat it like that, then you have discrepancies to frustrate you. People who calibrate their Zone System to camera tests with gray card as Zone V rate their EI differently than box speed. Certainly it will not agree with the incident meter at that point.

    These frustrations can interfere with your desire to "accurately interpret light intensity". You'll ask yourself "Why don't I get the same results when incident reading compared to when I meter the gray card?" Haa, I think you did ask that.

    I have a graycard from Sekonic that has several patches of gray. Trying to remember which one of those patches reads same as incident reading in same light has distracted me before. It's somewhere near the 12.7% patch. But remembering to pick the right patch - or using White paper and remembering how many stops that is from gray, is beyond my ability when taking pictures.

    Placing my palm on Zone VI is not that hard. And on top of that... I find it pretty well matches my incident readings.

  9. #69
    Alan Klein's Avatar
    Join Date
    Feb 2011
    Location
    New Jersey .........formerly NYC.
    Shooter
    Multi Format
    Posts
    590
    Well, I honestly have to say I don't use a gray card even though I have one. If I can read the light I need with a gray card, then I can use the incidence meter which is easier.

    Of mcourse, people shooting cameras with built in meters don't have that luxury. How are they calibrated by the factories?

  10. #70

    Join Date
    Nov 2005
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    5,837
    Quote Originally Posted by Alan Klein View Post
    ... people shooting cameras with built in meters don't have that luxury. How are they calibrated by the factories?
    Posts 57, 67, and 68.

    Plus a few additional tricks to improve the likelihood of good exposure such as center-weighting and matrix metering.
    Last edited by BrianShaw; 12-30-2013 at 10:49 PM. Click to view previous post history.



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin