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  1. #61
    Alan Klein's Avatar
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    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?

    E. von Hough: Have you actually tried 18% gray card measurement and incident readings with the Luna Pro in the same light? Do you get the same readings? If so, it appears then that your meter is calibrated to the 18% reading not the industry standard 12%.

  2. #62

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    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?

    E. von Hough: Have you actually tried 18% gray card measurement and incident readings with the Luna Pro in the same light? Do you get the same readings? If so, it appears then that your meter is calibrated to the 18% reading not the industry standard 12%.
    I was commenting on the Lunapro's low light capabilities, rather than it's calibration.

  3. #63
    kintatsu's Avatar
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    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.

  4. #64
    benjiboy's Avatar
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    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

  5. #65
    Vaughn's Avatar
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    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.

  6. #66

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    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.

  7. #67
    kintatsu's Avatar
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    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.

  8. #68

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    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.

  9. #69
    kintatsu's Avatar
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    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.

  10. #70
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    Quote Originally Posted by E. von Hoegh View Post
    Or you can just use a LunaPro.
    Luna Pro SBC, Nikon built in, Hasselblad 45° PME
    Warning!! Handling a Hasselblad can be harmful to your financial well being!

    Nothing beats a great piece of glass!

    I leave the digital work for the urologists and proctologists.



 

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