#22. "RE: Aperture, Shutter, ISO, and Illumination Relationships" In response to In response to 0
Ann Arbor, US
As an engineer, I'm always fascinated by tables that present clear relationships. For that reason, I really like this matrix of variables you created, Hal.
However: Very respectfully, I have to express my dissent with the content.
One of my favorite photography books is "Understanding Exposure" by Bryan Peterson. In his words (which is the way I also see it, hence I'm quoting him):
"A correct exposure was, is, and will always be a combination of your choice of the right size hole in your lens (the aperture), the right amount of time this light is allowed to remain on the digital sensor (the shutter speed) and the sensitivity to light (the ISO)".
The way I see it, achieving the correct exposure involves what the photographer can do to achieve it; other than few exceptions, the illumination is a given parameter that you need to work with. Sure, you can sometimes "help" by adding flash or close curtains on the windows, but these are the exceptions rather than the general case.
The image that is recorded on the sensor is simply a bunch of photons that were allowed into the camera: the photographer can only determine how many of them will be allowed, for how long, and how sensitive the sensor will be to record them. True, if we can influence how intense these photons are, it will affect how we set the components of this "exposure triangle", but so will other variables: we have filters, gels, we can change the polarity of the light, we have camera shake to work with, etc.
I think that there ARE only three variables involved in achieving a correct exposure; Illumination, like other external factors will affect the settings selected by the photographer and how the image will look. In engineering terms, I would consider it as a constraint, not a parameter that I can vary.