Response to Determining exposure index

Dear Rob, If you are going to use an 18% gray card, flash, and an incident meter, you can do the test accurately. However use of the incident meter REQIRES a 18% gray card. The indident meter should , theorectically, match a reflective flash meter of the same gray card. If you use a terry cloth that doesn't reflect 18% grey use of the incident meter won't match the reflective meter reading and won't be accurate. CAVEAT! One important variable you need to test for daylight shooting is the accuracy [and perhaps consistency] of your shutter speeds. The flash test wont do that. I suggest doing both. My bet is that you will get one EI for flash and one EI for out doors unless your shutter speeds are very accurate. John Elder

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