I'm trying to shoot a sequence of photos needed for calibration. As instructed, I'm in manual mode, with fixed ISO 100 (camera dafault), and other values read from the lightmeter ... and now:
Can you explain this passage?
Once you’ve determined your starting exposure, you will shoot additional exposures, incrementing the f-stop value by 1⁄3 f-stop using the manual controls on your camera. Shoot two stops on either side of the starting exposure and keep track of the exposures as you go along. I find it convenient to indicate the exposure change on the target itself by writing on a paper attached to the target. I write down the difference in exposure as a change in ISO. In other words, if I stop down one-third from the ISO 100 reading, I write 125: 2⁄3= 160, 1 stop = 200, and so on. The beginning of the sequence would go: 100, 80, 64, 50.
My ISO is 100 and it's not changing. Do I understand this passage as instructing me to change eg. F 2.8 to 3.2 and then to 3.5 then to 4.5, etc. 4 ... until I reach to F5.6? and these changes applied to the card as an ISO in a modified F? How then to do these measurements down by 2 stops (in the opposite direction from F2.8), as ISO must be constant and my lens can't be set lower than f/2.8?
I don't understand... Do I change time or aperture? Is my starting point from 4.0 and then 2 stops up and down?