I have this situation while shooting still life photos of e-commerce products, lets say for example leather shoes or leather bags:
- Table with white paper as white background.
- Two strobe flash lights with umbrellas at the each side about 45° angle (triggered by hot shoe trigger on camera) manually set power, no TTL.
- Canon 70D camera on tripod.
- Camera settings in "M": 35mm, ISO 100, 1/160, f8.0, Metering Mode: Evaluative metering. AWB Auto white balance enabled.
Given these fixed settings, all the pictures should show the same exposure no matter the object that is in the picture.
Instead I get different exposure depending on the object that I am shooting:
- If the object is big (like 50% of the frame) and let's say brown or dark blue, the general exposure appears darker.
- If the object is small (like 20% of the frame) and let's say yellow or pink, the general exposure appears more enlighted.
- I have some cases where there is a big exposure difference despite fixed settings for all.
I am facing this problem since a long time and I fix it in post production with Camera Raw. I have made research and tests on the camera with different settings to understand why it acts like that, but I can't figure it out
It looks like there is some sort of auto-exposure going on that I can't control or that I can't find on the camera settings.
Unfortunately I can't attach any example since I cannot publish the products photos.
I would like to know if is possible to have same exact exposure results giving fixed camera settings, without the camera making any auto-exposure (or similar).
EDIT : I cropped the same area on two different images, with same settings in all, but as you can see, the white background, who should be same grey, is darker in one and lighter in one. It is not a shadow since the more or less brightness affects also in the object itself. The image looks overall brigter or darker. The black areas are the objects that I had to erase because I can't show or publish them.
EDIT2 : Investigating in Adobe Bridge I found a very weird thing, even if in the metadata the settings are f8,0 1/160 ISO 100 35mm for both images, in the Exif data it says: 24mm max value f/3.8 for the first image, 135mm max value f/5.7 for the second image. That's pretty strange... Is it possible that would be a hardware error of the lens sensors?