Your test is flawed from the start. An 18% gray card is middle gray that reflects 18% of the light that illuminates it (18% reflectance). A styrene ball, being porous, will have a much lower reflectance value that 18%. So, using a reflective light meter, I owuld never expect to get the same exposure value when comparing an 18% gray card and a styrene ball (even assuming your styprene ball is really middle gray).
The Kodak Neutral Test Card tells you to hold the card in front of the subject so that it faces half way between the camera and the main light.
Importantly, it also states (this quote is actually taken from "Kodak Professional Black-and-White Films" but the card instructions say the same): "If you make a reflected-light reading from a gray card with incandescent illumination in the studio, use the exposure indicated by the meter. If you use the gray card to determine exposure outdoors in sunlight, increase the exposure indicated by the meter by 1/2 stop."
In dimly lit scenes, you can use the 90% white reflectance side, keeping in mind that there is a difference of five stops between your neutral gray and white (18% and 90% reflectance).
Bruce Barlow
author of "Finely Focused" and "Exercises in Photographic Composition"
www.brucewbarlow.com
However not everyones palm should be placed on ZI as pigmentation varies. Just saying as mine never reads one stop brighter than middle grey. But do I meter off it and place it on ZI in a pinch? You bet. Always gets me in the ballpark. In changing light with rapidly moving clouds etc. It gets me a quick relatively accurate exposure right off. Then for the next exposure I can take more time.
Thanks,
Kirk
at age 73:
"The woods are lovely, dark and deep,
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep"
Haaa, yes I keep forgetting people differ, and this is just what works for ME.
swmcl, if reading YOUR palm and placing on ZVI matches the reading from incident mode... Then, like me, you'll have a confidence-building quick check.
At least you will catch BIG mistakes like incident metering the light falling on your ear when you think you are spotmetering.
I went through the same doubt when my meter was new, and I was about to remove the K factor from the meter (because you CAN).
Until I found this much better plan... By USING the Zone System meter-and-place technique to confirm the Incident Mode.
I gave up the confidence-shaking result of working with a Gray Card and trying to remember the exact relationship.
Sorry, Bill.
Incident metering is significantly more accurate in all cases than using the ZS.
Of course this assumes that you haven't mucked with the meter's calibration.
The ZS relies on your perception of tonality, which is imperfect even in a highly experienced practitioner.
The perceived reflectance (tonality or "zone") of a surface varies due to many factors.
Human perception of reflectance can be influenced by color, angle of incident light, angle of surface to line of sight, and reflectance of adjacent areas.
It's easy to demonstrate this fact by simply spotmetering a gray card at different angles.
That's why the instructions tell you to position it quite specifically relative to incident and lens axis.
- Leigh
If you believe you can, or you believe you can't... you're right.
Gray cards fade with time and with exposure to UV.
Sounds like apples and oranges in technique. Either paint another flat card and then match the styles of reading, or recognize that you need to do an incident reading rather than a reflective reading from the ball because the shapes between flat and curved, no matter how small an area, change how the light reflects from the curve surface.
"One of the greatest necessities in America is to discover creative solitude." Carl Sandburg
Disagree. This maximizes the (unwanted) specular reflection. Use your gray card with sun incident at 45°, and meter staring along perpendicular. Please try and report back.The card should be oriented such that a line perpendicular to its surface bisects the angle between the light source and the camera.
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