How to expose

For many this is going to be the core of all the course, because the Exposition is something that has not changed in the digital realm. As for me the concept that I like most is the Triangle of Exposure.

It is like the Combustion Triangle, in which there are three concepts that will support the main idea. I have acknowledge of other concepts like the one with the tap and the bucket, if you want that I explain it leave a comment. To start with, the three concepts that put together the Triangle are:

• Film sensibility (ISO/ASA/DIN)
• Shutter Speed
• Lens aperture

Each one has its distinctive features, effects and priorities, which all will depend on how you would like that your photography is going to be.

I am going to discuss it in the order I have listed them. Essentially because in the film we are restrained to have ONE and only ONE film sensibility, there are some considerations if we intend to do forced or counter-forced expositions, and even in those cases, we have to shot the entire roll in one sensibility, not as in digital, in which we can change at will the sensibility to adjust to our needs in each shot.

This is one of the reasons I like more film photography, you have to choose what film to use, and you are restrained to make each one count as the good, even if you do not enlarge it.

Film sensibility

At the very beginning of photography this was not a very used term, this was photographers were able to use safelight to develop and only existed plates, so to develop them they used trays. They made the shot, with some known time and aperture, and then during the developing process they could see how the image appear and stop the process when they tough it has reached the best image. But as photography was becoming more mainstream, due to cinema and companies like Kodak, research and new technology changed the films sensibility to light and with it, the need to name that sensibility.

In the United States the American Standards Agency (ASA, now is it called ANSI), had the most influence in the Americas and Japan about how to call the film speed, while in Europe was Deutsches Institut für Normung (DIN) the one responsible for such labor. It is something like International System of Measurements and Imperial System, both told the same thing but with different scales, each institution made their own experiments on how to determine film speed. As time advance to a much more standardized World, International Organization for Standardization (ISO) was born, this Organization decided to use the two systems, so when one buys a film in the box comes as ISO 400/27º. I, as a Mexican, live under the ASA concepts then adopted by ISO. But both scales are direct one with another, interchangeable without any mathematical operation or so, not as 1 ft moreless equals 0.30 m. Most common values are:

ASA        DIN

50        18

100       21

200       24

400       27

800       30

1600     33

3200    36

As you can see ASA scale work with doubles and halfs, 100 being the double of 50, and 1600 being the half of 3600. In the other hand DIN goes in sums of three between each other, as 18 plus 3 gives 21 for the next film sensibility, but as long as now I have not explained what this numbers represent. 

So now going on, the smaller the number the lesser the sensibility is going to be, this means it is going to need a lot of light to be well exposed, and as the number goes higher the sensibility grows with it, meaning you will not need many light to have a good exposure. And the relationship each one with the another is going to be the doble or the half. Ej. lets took ISO 100/21º, if we go to 50/18º this will tell that we are going to need the double of light to have a good exposure, compared to 100/21º, and viceversa with 200/24º, it is going to need the half of light needed for 100/21º to get the same exposure. But the next question is going to be, Why to have different film speeds? If we are able to shot almost in any condition with 800/30º, for example.

Well there are some cons and pros, depending on which film speed we are intending to use. Film speed is also related to the size of the silver halides the emulsion contains, as smaller the number is, the salts are going to be smaller, which is going to be handy if we want to have the most definition of the image we intend to capture, very useful in landscape, product or studio and maybe portraits. But with the cost of needing a lot of light to achieve a good exposure, so in the cases of landscape tripod is going to be mandatory, in the studio, well we are going to be controlling light via lamps, flashes and using an exposure meter, and in portraits, well as we are going to see later,  wide open lens apertures; we also gain better contrast* with lower ISO values. That is why the largest photos ever are made with low ISO values, as it grants the best definition. But in special cases as sport photography, scientific, and places in which light is not the best of all or we need to achieve the photo we want, the cost is a little loss of sharpness and contrast, as higher ISO values have bigger silver halide grains. 

A way to classify higher or lower ISO's is the next: take for instance 100/21º as the mid-point, below that value, even as low as 6/9º they are called slow emulsions or films, as explained earlier, a lot of light is needed. Then, from 100/21º to 400/27º are the mid-term speed films, more likely as the standard, as you have a balance between outdoors and indoors using artificial light (as lamps or flashes), and medium sized grains. Higher than 400/27º are called quick films, as low light is needed to expose.

The last technologies applied to Black and White photography were made by Kodak and Ilford, as they in the late 80's and 90's developed their T-Max and Delta series. They found a way to give the grains certain shape, Kodak saw T's and Ilford saw ∆'s (capital letter delta), which made possible to arrange them better, and with that more sensibility with smaller grains. Both films are marketed as Pro films. As I know Kodak sells T-Max 100/21º, 400/27º and 3200/36ª (really 800/30º, but can easily pushed to 3200/36º), and the best results are given if you develop with T-Max developer (very self-explanatory) and in the other hand Ilford's are 100/21º, 400/27º (can be used as 200/24º to 3200/36º) and 3600/36º (really being 1000/31º, but can be pushed to 12500/42º), the best results with this films are obtained using at least ID-11 developer, but are better using Mircophen.

So before hitting the street with you camera, and if it isn't loaded, stop and think to which situations are you going to be facing, because that is going to be the best parameter to select a film. If you are going to be out in a sunny day, without any trouble you can use ISO 100/21º, but if you are going to be in a familiar reunion inside a house better choose 400/27º, or any sports event better go higher, even if it is sunny.

*Contrast, for me, is like how intense are the whites and the blacks. For example: in high contrast you will only see whites and blacks but not so many grays, in low contrast you will not see white or black just a big range of grays. Depending on what are you going to achieve at the start it is better to look for a medium contrast, the one that is going to have white, black and the variety of grays.