This illustration is done by facing the white bag on cam at my chair and setting the settings that way.
I also tried (by checking my historgram and settings that I receive a slightly faster shutter speed (1/13 sec without the roof light vs 1/15 sec with the roof light on in the room). This is done w/o the roof light.
Another thing I found – I took images with the flash (with bag on lens) at varying settings. The one most accurate (peak in center of histogram box) turned out to be FLASH EV MINUS 2/3 or 1.66.
Norm Dunne
Lover of the Old Masters Art Period