I was doing some tests at my school with an Alexa. I wanted to do graphics with the different EI : Luma value of a Kodak grey card = f(stops from -10 to +10) basically.
I wanted to do this both in Rec 709 and Log C but only did the 709 tests as of yet.
For each EI I placed my "+0" by spot metering the grey card, but noticed two things.
1/ As I kind of suspected, it wasn't falling on the 50% IRE (512,512,512 when shooting Rec 709 in 10 bit)
2/ My Sekonic gives me half a stop of difference between spot metering of that 18% grey and incident reading (when the spot was reading 5.6, the incident gave 4 1/2)
So I kind of have three different possibilties for my zero.
Which one should I use ? Is that true that Sekonics are set to read 12.5% grey card instead of 18 (which I guess would explain the weird difference)
When a cinematographer says he places a caucasian face on +1, which one of the three 'zeros' is he refering to ?
Ultimately, do we place the grey card anywhere we want between say 30 and 50 as some people suggest ?
That's all I have to ask for now, hope the questions make some sens !
And I hope it hasn't been asked and answered a thousand time.
Tom Yanowitz, film student