Part 3 The Course

So in the previous two parts we have covered aperture and shutter speed, the last part of this equation is film speed. It is very important to understand how and why film does what it does because you will need to understand what is going on for those very tricky, but worthwhile shots. THIS ALSO NEEDS TO BE UNDERSTOOD EVEN IF YOU USE DIGITAL ALL THE TIME! Now film speed can be known as ISO ASA DX Din. Basically they are all the same thing. So let me explain firstly in detail how the photographic process works. A film is merely a strip of clear plastic that has chemicals attached to it. These chemicals are sensitive to light and when light is placed on them they react. Now if you foolishly took a brand new roll of film and pulled it out of its cassette so it is flooded with light that chemical reaction would take place. However if you stared closely at it for a day, week, month, or even years you wouldn't see any difference. No to actually see the outcome of that first chemical reaction requires a second process known as developing.

The film now exposed to light is placed in a chemical known as developer which reacts with the film chemicals and actually physically changes their properties.This physical change is what produces the image. So if we understand how and what is going on it is far more likely we will be able to choose a film speed to suit what we are trying to photograph.

In the above example by simply exposing the whole film to light after the developing stage we would have a very dark piece of plastic with all of the original chemicals on it. The light would have reacted with the whole film. So let me explain what actually happens. Look at the picture on the right here. You will see two portions of film both over the picture of as pretty girl. (Why not!). Both have been through the developing process and number one you will see is transparent and number two is black and opaque. Number one was not exposed to any light and number two was totally exposed to light, before the developing process. So you can see that if not exposed to light the chemicals appear to be washed off the film. If exposed to light the chemicals become dark and stick to the film. Yes that is it exactly.

When your camera shutter opens, light from the scene floods onto the film. The bright light will hit the film and those chemicals will be made sticky, where the light doesn't hit the film the chemicals will be washed away. Obviously where you have shades of light and dark the chemicals are affected to differing degrees. This will produce a negative, so called because what was light is now dark and visa versa. Now this all holds perfectly true for black and white film, but obviously there is more involved with colour. I don't think any of us need to become chemists just to take great photographs, what is much more important is that we have a mind model of the process so we can understand what is happening. The second article below does go into greater detail. So on that note and keeping it really simple I'll explain further.

The chemicals on the film are crystals. Each crystal is affected by light as we have said. If light hits it a reaction takes place that causes the crystal to turn dark and remain on the film during the developing process. If no light hits a crystal then it will have no chemical reaction and be washed off. Now if we have big crystals in our chemical goo, then light hitting the film will react quickly. If we have tiny crystal and obviously lots more then the shutter will need to remain open longer for a reaction to take place. So in simple terms, big crystals mean fast reaction, small crystals mean slow reaction. Hold that Thought!!!

I said earlier a negative is produced. This has to be turned into a print and the method is simple. Light is shone through the negative onto a piece of white paper that has exactly the same chemical mix as our film. Hence the light parts of the negative let light through and the dark parts don't. So we then simply get a positive from our negative when the developing process is given. I am sure you all know that anyway. My point here though is the image is also magnified during this process. So if you have big crystals and magnify a lot you will be able to see the crystals in the print. This is called grain. Small tiny crystals will not be so apparent and allow larger magnification.

OK so you held that thought. Slow film produces finer prints than fast film which is grainier. Is that all I wanted to say about film? If only :-)

So why again I hear you ask do I need to know this especially if you use digital? Well in all fairness modern film has improved so much grain really isn't an issue any more, however if you are producing work that will be printed to any size you really must think about grain. If you use ISO400 film with a 35mm camera and want a print of 20" x 16" you will have grain that will definitely be perceptible. In fact in my college days using 800 asa film and blowing them up huge was all the rage. Just like scribbling round the outside of the negative is now.

There will be occasions when you have to work in low light conditions and this is when you need to understand what your film speed does for you. This is also very true for digital cameras. By selecting a higher ISO number it allows the CCD chip to work faster by making the individual receptors larger , but at the same time using the trade off of detail quality.

If you have big crystals you cannot have fine detail. If you wish the CCD in your digital to work at low light, but at a fast enough shutter speed to stop camera shake it will have to be traded against quality of detail.

Below is a close up of an eye and you can see the individual pixels, so you can see if each pixel is four times as big you start to lose outline definition and detail. So that's for you guys with digital, and think crystal for pixel if you are using film. With film of course the crystals are not all a uniform shape and size.

I am sure you are wondering why I have gone on and on practically beating you over the head with this. Please understand this because it is so basic to taking good photographs and people just don't seem to feel the need for it in this digital age. And you do, or will later on in the course.

Now you have been browbeaten I will move on!

If you use film you will find that different lighting conditions will give different effects. You can read all about this in previous articles where the subject is covered in great depth. These articles are MUST READ because they cover the other aspects of film , and are very important to understanding what you are doing.

Close window to return Understanding Colour and how film sees it.

Close window to return More about colour

Close window to return What is the colour temp of light and does it matter?

That just about says all I want to say for now on film. Next month we actually get into taking a picture. Yes seriously you can start next month to actually think about taking a picture. :-)

This months project.

Use a slow film. and an ultra fast film and try and take the same subjects.

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