The Exposure Value

Blog, Pocket Full Of Fatcaps

Sometimes it’s difficult to know the values for a correct exposure. For example if we want to photograph the lights of the city at night the reading will be inaccurate because those distant sources of light are not intense enough to affect the exposimeter; Or maybe when we want to figure out if the 400 ISO film we have at home will allow us to take perfect photos with our Kodak Brownie during a sunny morning with the fixed settings of this camera (f/16 and 1/30).

There is a solution, but is a bit complicated!

What we’re going to know and use is the “Exposure Value” (EV) which is a unique number that indicates the brightness of a scene.

It is obtained by using a mathematical calculation referred to a sensitivity of 100 ISO:

EV_Formula

Obviously the same exposure value can be obtained with different combinations of the three parameters (ISO/A/T) which is also the concept at the foundation of exposure and photography.

Leaving aside all the mathematical part, we can simply use one of the many charts that we can find on the net, or the one that I propose below (referred to 100 ISO):

Now to take advantage of the EV you have to connect it to the Sunny 16 rule (on a sunny day, with sharp shadows, to get a correct exposure you have to use f/16 and a shutter speed as closest as possible to the ISO of the film you are using). The EV is a calculation based on 100 ISO then, comparing the values of the Sunny 16 for the same value (f16 and 1/125) with those on the EV chart above, we derive that 15 EV is the amount of light that is present on a sunny day with sharp shadows!

Below I suggest an exemplary data table of how to exploit the EV value in combination with the Sunny 16 rule based on different iso settings but keeping 1/125 as shutter speed:

So I took the EV, I’ve mixed it with the Sunny 16 and I’ve got a handy data table to “guess” the perfect parameters for a good exposition: now you have to simply rearrange the table with your favourite shutter speeds, ISOs and apertures. I know that is a difficult mathematical exercise so I’ve done it for you 😉

A practical use of this value, as I mentioned, is to help us decide which film we can use referring to the  amount of available light there will be in the scene that we are going to shoot. Or maybe it will help to understand the shutter speeds and apertures needed in conditions where the meter will not function correctly.

Transforming this knowledge into a practical example we can say that if we have to shoot at an indoor sport event, which we know have an EV of 7, we cannot take with us a 400 ISO film, because the camera settings will be f/2.8 1/60: too slow for almost every action.
At least with 800 ISO we can have a shutter speed of 1/125, but may be f/2.8 may result in a too narrow depth of field.
The best decision will be to use a roll of film that tolerate being pushed to 3200 ISO without losing too much quality so we can select an array of settings between f/2.8 + 1/500 or f/4 + 1/250 or even f/5.6 + 1/125. That will be enough to let us choose between a faster shutter speed or a deeper DoF.

Metering without a light meter

Blog, Pocket Full Of Fatcaps

In old film cameras sometimes happens that the exposure meter batteries runs out, or that the selenium cells pass to a better life just at the wrong time or simply that the camera does not have a light meter!

How to solve this problem? With an old “rule” that our grandparents had discovered to “guess” the exposure. In reality behind it there are calculations, experiments and a fine knowledge of the medium 😉

The so-called Sunny 16 rule says that on a sunny cloudless day to achieve the perfect exposure you need to set the aperture to f/16 and the shutter as close as possible to the ISO of the film you are using.

So if I am using a 400 ISO film I have to set the aperture to f/16 with a speed of 1/500, for 100 ISO I will use 1/125 and so on.
After having applied this rule we can change aperture and shutter speed depending on our needs! For example if I’m using a 200 ISO film I should use f/16 and 1/250, but if my need is to photograph a fast moving cyclist, I can push the shutter speed to 1/1000 (2 stops) and compensate increasing the aperture of 2 stops up to f/8.

This is fine for optimal lighting conditions, with a strong sun that casts sharp shadows, but the same rule can also be applied to other lighting circumstances and the only change will be in the aperture settings. Thus, in a not so sunny day, in which the sun creates soft shadows, we will use f/11 instead of f/16, while for a cloudy day with barely visible shadows we will use f / 8 and, for a cloudy weather without visible shadows (or for shooting in full shade), we will set the aperture to f/5.6.

Sunny 16 rule computed for the most common times and ISO settings – Click to enlarge

In “special” conditions, for example shooting in highly reflective environments (snow or white sand), you can use f/22 while for a sunrise or sunset the aperture can be set to f/4 reaching up to f/2.8 for the minutes before of the sunrise.

In case of backlight as a general rule, whatever may be the “power” of the light source, to have the subject properly exposed is necessary to apply the rule and then increase the aperture by two stops.

The Sunny 16 does not stop there, but also helps us in more specific and extreme conditions: for example we go down to f/2 if we want to photograph neon signs or earliest sunrise and sunset glow, f1.4 to expose the fire, shop windows after sunset or night outdoor events and f/1 to shoot indoors (with bright light) or indoor events.

It should be remembered that then in the darkroom, when you go to print the image, or when we scan the negative, we have a margin of at least one recovery stop, so it’s pretty hard to fail completely the exposure

Ferrania Eura: the two apertures available / I due diaframmi disponibili
Ferrania Eura: the two apertures available / I due diaframmi disponibili

I would like to add that this rule is the basis of the construction and utilization of some old cameras, back in fashion a few years ago with the Lomographic wave, such as the Kodak Brownie.
The Brownie has no controls: fixed focus to infinity, fixed aperture (f/15) and fixed shutter speed (approx 1/30) that allow it, with a roll of 100 ISO film, to make well exposed photos.
Or the Ferrania Eura wich has a fixed shutter speed of about 1/50 and the possibility to choose only two aperture: f/12 for sunny days and f/8 for the cloudy ones!

These cameras should only be used under certain conditions, but mastering the Sunny 16 rule, we can calculate the correct film speed to take advantage of the native settings for our needs: for example, mounting a 400 ISO film on a Ferrania Eura, make it possible to use it in conditions of full shade so with 2 stops of difference.