In the film days, I would shoot tests on new film stocks to determine how the negative responded at various levels of over and under exposure. Think of it as establishing the usable or practical dynamic range of a particular film stock. Those tests were my guide to the pre-visualization of my lighting — which areas of a scene would be lit to the stop I had chosen for the scene and which areas should be under or over exposed and by how much.
Although digital images can be evaluated in real time, I still light using incident and spot meters. I conducted this test to establish how the GH5 sensor responds as it is over and under exposed. Normally, I would have included at least one model for a real skin tone reference, but because of the pandemic I have restricted the test to the well known X-Rite ColorChecker Video chart.
I don’t shoot log at this point so I used my usual settings.
- ISO: 400
- Rec Quality: 4K, ALL-I, 400M, 24P
- Photo Style: Natural — Contrast, Sharpness, Noise Reduction, Saturation, Hue settings @ 0
- Luminance: 64-1023
- Lens: Voigtlander 42.5mm f/.95 Nokton
- Lights: Aputure hr672 daylight
Color Balance was set using a Lastolite EzyBalance Gray Card. Color temperature was checked at each light level change and varied no more than 50 degrees kelvin from the 5600 degrees kelvin baseline.
UHD files were imported into Premiere and trimmed to approximately 5 seconds for the slates and 15 seconds for each exposure. No correction was applied to color, contrast or exposure. The over and under timelines were output as 1920 X1080 MP4 files.
BTW – There is a handy rule of thumb for converting foot-candles to f/stops at various ISO settings. Use the following formula — 100 foot-candles at ISO 100 = f/2.8 — extrapolate from there.
I managed to shoot the +2 2/3 EV twice — thus leaving out the +2 1/3 EV. Also, there is a noticeable reflection of the left light on the darkest wide strip at the bottom.