ABSOLUTE BEGINNERS – MAKING SENSE OF THE NUMBERS

This is the first of our absolute beginners tutorials, in this tutorial, we’ll attempt in plain English to guide you through the absolute basics of what a camera is, how it works, and along the way take a look at some of the features and terms you hear whenever people get together to discuss photography.

For this article, we’ll gloss over many of the camera’s ‘bells and whistles’ and just concentrate on the very basics which should give you a good grounding.

It should be easy right? After all, a camera in it’s simplest form is a box that lets the light in at one end through a hole (which for the sake of argument we’ll call an aperture, because that’s it’s name) and has a medium that is capable of recording any light that reaches it at the other end. This may be a film, a plate or even a digital sensor. For the most part, they all do the same thing and are always in exactly the same place – at the opposite end of the camera to the aperture. Photographers being photographers couldn’t just leave it at that, it needed a name, so, the place where the photograph is actually recorded is called the ‘film plane’. If you’ve ever wondered what this little icon on your camera is

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That’s the one telling you where the film plane is. For 99.9% of the time it doesn’t matter, it’s there and that’s it but if for example, you are taking panoramic photographs then it becomes important. Keeping it simple, you want the camera to rotate around the film plane to get a smooth transition between the various elements of your panorama.

A box with a hole (aperture) in the end was never going to produce high quality images so lenses were introduced, carefully shaped and positioned to focus on the film plane. Photographers quickly realised that the bigger the lens, the more light got into the camera, the better the quality of the image and above all shorter ‘exposure times’ or the length of time the photographic material needed to be exposed to the light to record the image could be reduced. In real terms, this meant that the subjects of the photos didn’t have to sit perfectly still for so long.

A modern shutter works in much the same way, as you press the button, it opens and lets light pass into the camera for a precisely measured time, just long enough for the camera to record the image and then closes again, sealing the insides of the camera from any more light. The exact amount of time the shutter remains open is called the shutter speed and is (for the most part) measured in fractions of a second. 1/100, 1/500, 1/60 etc

How long we want it to stay open varies depending on four major factors, let’s have a look at them.

The first governing factor is; How much light is available? A camera can only record what it can see.

For this section, we’ll take two examples. A bright sunny day and a dull overcast one. The light on the bright sunny day is far more intense than it is on the dull one, let’s assume it’s twice as bright therefore, if our only control over the camera’s exposure time was the shutter speed, then a photograph taken on a dull day would need to be twice as long as one taken on a sunny day in order to get the same amount of light into the camera.

On the dull day you may use a shutter speed of 1/125 but to take the same picture on our sunny day you would use a shutter speed that opened the shutter for half the time i.e. 1/250.

Of course, it’s never that easy. So we’ll add another variable which we can control. Let’s consider if the aperture in the camera was letting in too much light. It may be perfectly configured for the dull day but a hole that size would let in twice as much light needed to take the picture on a sunny day. What was needed was a variable aperture. Just like the pupil of your eye, cameras need to be able to reduce the amount of light entering the camera they do this using a series of interlocking plates called an ‘iris’ meaning that the aperture could be controlled and made smaller and wider to let more (or less light into the camera). On our bright sunny day, the aperture could be reduced to a tiny hole, on our dull and overcast day it could be increased to a larger one and still let in the same amount of light whilst using the same shutter speeds. The amount by which the iris which opens and closes is set to intervals – these are referred to as ‘F stops’ and appear on your camera as markings like f2.8, f8 etc. Each one represents a position of the leaves in the iris and tell you how much light is getting in to the camera. As confusing as it is (and of course it is very confusing) it’s important to remember that a smaller number means a bigger aperture and a higher number actually means a smaller aperture

Don’t ask ‘why?’ because that would just become very technical and confusing. At this stage we aren’t getting that involved and it’s certainly not important enough to justify getting wrapped up in a maths class when all we want to do is take some pictures.

A quick example for you would be that if a photo taken in low light at f8 needed an exposure of 8 seconds, the same photo taken at f5 would need an exposure of 4 seconds, at f2.5 one second and so on. remember, the lower the number, the more light is getting into the camera.

Using this method to regulate the shutter speed is called Aperture Priority and will be one of the options in your cameras settings. It gives a great deal of control over how you take pictures and has been very popular with photographers since it was first introduced onto cameras in the mid to late 1960’s

You set the aperture you want to use and the camera decides the ideal shutter speed for the conditions giving you (in theory at least) a perfect exposure.

Your camera will also have a setting for ‘Shutter Priority’ . Here, depending on the subject matter, you decide the shutter speed you want to use and the camera software calculates the required aperture. Of course, if you take full Manual control of the exposure you have to balance the aperture and the shutter speeds yourself. Usually using a meter which is built into the camera

Still with us? Good.Just to recap then.

Light gets into the camera and we control just how much of it we need. Too much light and the photograph is over exposed, too little light and it is under exposed. By using the aperture and the shutter speed we can ensure that just enough light gets through.

If only it were that easy, but as you’ve probably guessed, it’s not. We can now add another variable into the mix and it’s called ISO (or more recently ASA) values. ISO values were given to film and denoted how much light needed to get to the film in order to record an image and (in order to keep it very simple) referred directly to the number and size of light sensitive particles on a piece of film or a plate. Your digital camera doesn’t have film but equivalent values have been given and whereas to change from one ISO rating to another on a film camera would require a whole new roll of film on a digital camera you can have as many different ISO values you like on the memory card.

A lower ISO film number such as 100 made of many small light sensitive particles would only be useful in good strong light but to take a photo in low light you would need to have both the aperture wide open and the shutter open for a long period to allow the required amount of light into the camera. Faster films were developed. Using a lot less larger grains of light sensitive material so that the exposure time would be much lower. The trade off was that the larger particles lead to ‘grainy’ images.

Exactly the same applies with your digital sensor. At lower ISO values, the sensor uses every pixel individually to record the light coming into the camera and that gives you better quality images as the maximum amount of data is recorded. As soon as you increase the ISO rating, the camera begins to group the pixels together in order to use the light coming into the camera more efficiently.

The downside is of course, the higher the ISO number, the lower number of individual pixels in the finished photo means that your photos are less well defined***.

Whereas the aperture and shutter speed combine to control the light flow into the camera the ISO rating sets just how much of that light we need to record an image and as photographers we control them to give us the best results.

So, we now know that the available light can be utilised by shutter speed, aperture size and ‘film’ speed and hopefully it’s still making sense.

Let’s make it a little more complicated then.

Aperture of a lens doesn’t only affect how much light gets into the camera (that would just be too easy wouldn’t it?) The wider (lower number) you use the narrower the ‘depth of field’. This is something that you’ll hear photographers talk about a lot and in plain English it means the bit that’s in focus. Nothing more, nothing less, it’s as simple as that but you need to understand how it works and how to use it to your advantage.

If you were taking a picture of a landscape. The most important thing is that the whole picture is sharp and in focus so it’s best to use a narrower (higher) number aperture as that will give you a greater depth of field. If you were to take a portrait of somebody and wanted the background to be blurred then you would use a much wider aperture which has a much narrower depth of field.

A fast moving subject such as a racing car or a running animal will need a higher shutter speed in order to ‘freeze’ the action. You can achieve this by opening the aperture as wide as possible to reduce the shutter speed. If that’s still not enough, then you can always increase the ISO to make the camera faster

A close up portrait will look better with a narrow depth of field keeping just the subject in focus and the rest of the picture blurred – this is usually called Bokeh* and is often the subject of many long and often tedious discussions between photographers about what is good and what is bad. Generally speaking ‘good Bokeh’ is smooth, easy on the eye and adds to the main picture, ‘bad Bokeh’ is harsh, unpleasant to look at and detracts from the main picture. The quality of the lens is the main governing factor here, so try not to get involved in those discussions as they invariably turn into a ‘my lens is better than yours’ contest

Depth of field is very important in Macro (extreme close-up). The closer you are to your subject, the less depth of field you have to work with so remember to choose your focus point very carefully.

That’s it for this article. We’ve covered the very basics here and in future we’ll go into more detail and hopefully you’ve found something interesting and informative.

Please remember, the purpose of these tutorials is not to tell you how to use your camera, all we are doing is telling you how a camera works. The rest is up to you

If you have any questions or you would like to know, then please join up at our forums and get involved in the discussions.

* Bokeh explained in some depth here in this Wiki article http://en.wikipedia.org/wiki/Bokeh

***Of course, this is just a very simple scratch the surface explanation but it should suffice for now

November 2017
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