So much of digital technology has allowed a method of creativity my old electronics professor would label “plug and chug”; swap a piece out, see how it works. In his words and my sentiments; not so elegant. As in many life pursuits, creating with intention can give us perspective, meaning and impact on the world and those around us.
Apply this to exposure, your f-stop (t-stop if you will…). Do you choose yours or does it choose you?
When you start to take command of your f-stop (quantity in the quantity x time equation of exposure) you begin to better understand the nature of light, depth of field, optics and perspective. This is because you need to understand all this to command your f-stop.
Working towards our chosen f-stop, we need to consider the methods of controlling the amount of light hitting our “target emulsion”. Can we control the light source at the source, or do we control it at the subject? Controlling closer to the source, the effect is broader and less refined; distance results in accuracy yet threatens the frame.
With flexibility comes complexity.
Perhaps our only “quantity” control is available at the camera, through use of exposure index, gain or neutral density filtration (leaving that f-stop put…).
While depth of field is the most common reason for “choosing” an f-stop, there are other reasons. Maybe you need to balance your “theatrical” lighting with practical sources. Perhaps the iris of your lens has an inherent sweet spot that minimizes aberrations, or perhaps you want to use that aberration as a cinematic element.
Did you know that for a constant f-stop and image size, depth of field remains constant regardless of focal length. If you know how to “work” a DOF chart you can prove me right. I first encountered this rule as a young studio camera operator on a multi-cam show for Hearst Broadcasting, a delightful series of exercise videos featuring Cosmopolitan cover girl Carol Alt. The director wanted to isolate our star from the busy background so he had me move further and further back, using a longer focal length to maintain the required medium shot. We ran out of room, as you will, before DOF became shallow enough. Finally, I convinced the director and the engineer to dial in a neutral density filter and open up a couple stops. Voila!
Start to take control. A great tool to experiment with is the P-Cam app for iOS. With it’s richly featured set of tools you can experiment with f-stops, exposure and depth of field for most formats, film and digital.
Going old school? Try David Samuelson’s “Hands On” Manual for Cinematographers, or the ubiquitous ASC manual.