Photo 101 – Basics (Part I)

Exposure Value (EV) is something we have all ignored at one point or another in our life but when you look at it in the cold light of day there is nothing to it at all.

EV is nothing but a fancy name for a combination of aperture (part II) and shutter speed (Part III) that describe the same exposure.

Let tell this in a story .... Say you are out one day and decide to take a picture. You feel brave enough on this sunny day and set your own aperture and shutter speed, by doing so you have told the camera that I want you to set this combination as EV 0, a benchmark of sorts. (Extremely simplified but should get the point across)

You take a landscape picture and find that the sky is bleached, more white than blue. This means that you are over exposing you picture to light and probably have your aperture to wide or shutter speed too slow.

Now you have two options
a) Change the aperture/shutter speed, giving the camera a new set of benchmark and effectively re-setting the EV 0 value, or

b) Simply lower your EV value to say, -1/3 (normally EV values go up/down in thirds or halves in the range between ±2)

The second option is a quick way of fixing your settings to achieve the same goals. I will revisit this in Parts II & III and hopefully it will put the whole thing into context.

Before I bring this to a close I would like to point out that ISO, the sensitivity of the film, an age old constant of sorts has now joined the ranks of the “variables” and technically should be considered as a component of the EV. (More on this in Part IV)

In summary (at the risk of alienating people by introducing unduly math):

EV is dependent on (or a function of) three variables; aperture [Ap] (Part II), shutter speed[Ss] (Part III) and ISO (Part IV))

" EV = function (Ap, Ss, ISO) "