Spot meter advice, No.2

[GPS]

Mark, I'm slightly afraid, your solution is rather a chimère... "When angled correctly..." - and how do you decide the "correct" angle?
...
You can get a whole plethora of readings while juggling with the gray card - how do you know (a priori) what is the correct angle?

Yes it does answer the question.
The answer is that testing using a gray card is the best option and you're going to have to live with the vagaries that comes from having a "plethora" of readings depending on the tilt of the card -...

Question:How do you(a priori) know what is the "correct" angle?
Answer: Testing using a gray card is the best option ... you have to live with ... a "plethora" of readings...

Yeah, Cyrus, - when it rains, some people use an umbrella and cheese is good as is to wash your hands...

[cyrus]

Question:How do you(a priori) know what is the "correct" angle?
Answer: Testing using a gray card is the best option ... you have to live with ... a "plethora" of readings......

the standard use of the card is to place it at 45 degrees. if it is 40 or 60, it may cause a 1 stop difference. If you put it at 20 or 90, then you're an idiot.

[GPS]

As the OP of this thread, I think it's about time I stepped in. I asked a question which seemed to have a multitude of answers, but thank you to Cyrus the answer was simply to do with the angle of the grey card. When angled correctly they readings of incident and reflected match, as I would have expected, and perfect exposure for the picture in question.

How do I know it was a perfect exposure? A black bag against a white wall, looked exactly as that, a black bag against a white wall. NO Zone system, NO find the true ASA of the film. NO under/over development.

the standard use of the card is to place it at 45 degrees. if it is 40 or 60, it may cause a 1 stop difference. If you put it at 20 or 90, then you're an idiot.

Nothing beats the "correct" 45° inclination of the gray card. Just put it at 45° (if you put it at 20 or 90 then you're an idiot) and the incident and reflected reading match - perfectly.
Or do they..?

[Stephen Benskin]

I'm in my office taking a picture of my camera bag, I take an incident reading, get exposure, it's bang on, then I put up grey card next to my bag and take spot reading, it says 1 stop less exposure needed. Does that mean something is wrong? I thought it should read the same.[/QUOTE]


Both meters are designed to obtain the same exposure, but to there's a few problems when you attempt to compare them. An 18% gray card is 1/2 stop brighter than the middle gray calibration value (12%). Also, the card needs to be held at a 41 degree angle from the light source and the camera. Finally, you have a potential spectral bias from the photo cell of any given meter. All of this can easily add up to the one stop difference you see.

Steve