Photography and Exposure

Photography and Exposure Settings - Getting It Right !

The modern camera

Today, cameras are getting smarter and smarter and can in many cases 'get it right' without any assistance from the operator. This is down to the sheer amount of computing power that even the simplest compact has these days, what with their 'face recognition' software and the like they can even guess what you want to photograph, and change all the settings for you.

All this is fine and dandy, but wouldn't you like to know how it all works, sure you can leave it all to the camera, just the same as you can leave a plane in auto pilot, but wouldn't you feel safer if you knew whyit did what it does, just in case you have to take over sometime???

How the camera sees the world

It goes without saying that the camera sees the world through it's lens and will capture just what it sees (with exceptions as you will see), the things that it captures including that tree sticking out of aunty Maud's head by the way (but that is a different story and is all about composition).

But what are the rules it uses to decide what to capture and how well??

The first and perhaps most important issue is that of what will be in focus. You see, when you look through the camera's viewfinder, using the fantastically adaptable thing that is your eye, everything is in focus, your eye adapting and changing to bring whatever you are looking at in focus. Not so for the camera, it can't take a photo with different 'settings' for the back and the front, no, it has to use one setting for all and that makes a difference, a big difference in some cases.

Depth of field

What will be captured in focus is decided by the size of the aperture (the F number) that the camera uses when it takes the picture, the lower the F number the more light that is 'let into' the camera, so F2.8 will let a lot of light in, while F22 will let in little. What number the camera chooses will be down to the other elements it has to juggle with, the ISO rating and the shutter speed, but more on those later.

The reason the F number is so important?

So why is this 'F' number so important? As it says above, it is F number that (along with the shutter speed) dictates how much light from the subject is going to be let in to form the image in the camera, and relates to the setting that the aperture (the hole that the camera uses to 'see' the world with), the smaller F numbers setting a big hole, while the larger numbers like F.16 setting a very small hole. But what difference does all this make?, why do you care what size "hole" the camera uses??

The answer is in fact that while big apertures let in a lot of light, they also reduce the depth of field, this being the amount of the image that is in true focus. You see, while you fantastic eye will use one 'setting' for the back and one for the front of the scene seen through the camera viewfinder, the poor old camera can use just one, and so even thought it all looks in focus to you, when the camera takes the shot, something's (if the camera is using a small F) number will be blurred, it is as simple as that. So the selection of the right F number is critical to what you are trying to achieve.

Some examples of F numbers and why they are the right choice

Let us assume that you are taking a lovely girl's face against a background in a garden. Behind her lays a plethora of flowers and plants, all wonderful in their own right, but not, I repeat not, what you want to capture, you want to concentrate the viewer on the girl's face. So how can you make sure that this happens? The answer is simple, use a small F number and the amount of the picture that is in focus will be limited to just the girl's face, the background will be blurred to just a mix of colours and vague shapes. The viewers eye will be concentrated on the face, and voila 'mission accomplished'.

Now let us assume that you want to capture a landscape, but also need something , maybe a flower, that is quite close to the camera, to be in sharp focus too. How is this done, well for the most part (there is the matter at which point you focus on too) this is down to the size of the F number, as the larger the number (and the smaller the aperture, the hole used) the more that will be in focus, which in turn means that given enough light you can use a small aperture and get it all in focus.

The amount of light is important

The observant amongst you will have noted the words 'given enough light' in the paragraph above, so what is that all about? Well we have been through the whole thing (excuse the pun) about F numbers, but there are two other things that the camera uses to create the image, these being the ISO number (the sensitivity of the film, be it old fashioned 35mm or it's digital equivalent) and the shutter speed (the time that the camera allows light in). The amount of light is thus important as there are limits to how much the camera can do when it comes to capturing an image if the light is low.

The ISO number

In the old days this related to the 'speed' of the film in a camera, and was basically down to how big each light sensitive blob on the film was. High speed films (like ISO 1600) had fewer, but bigger blobs and thuscould capture images when the light was low, while the low speed films (like ISO 25) had lots of smaller blobs, which in turn means that they needed a lot of light to capture an image. The downside of using a high speed film was the fact that with their smaller number of blobs, the images they rendered were just not as sharp and were more grainy and thus basically less pleasing to the eye. Today, the same goes for digital cameras as you can (in many cases) choose which setting to use (and of course suffer the same degradation of image as with a film camera when choosing a high setting). In practice this means you can by selecting a high ISO rating on your digital camera, take photographs in dim light, but just remember that the quality will be reduced.

The shutter speed

The final part of the triangle is the time that the camera sets the shutter at, this being the time allowed to let light in. Now again, why is this important? There are several issues to bear in mind here, the first is defeating the dreaded camera shake (unfortunately it is very difficult to hold a camera steady enough for long exposures - long shutter speeds) while the second is to capture things that are fast moving (like a man jumping a hurdle, or a dog leaping up to catch a ball). The whole thing is down to how fast the object you want to capture is moving, fast moving subjects needing a high shutter speed, while landscapes only need a slow shutter speed (cause they don't move).

Others thing to consider

There is another thing that needs some thought when taking a picture though and that is how much light is being reflected from the subject you are trying to capture. This is less important these days with the clever cameras that are available, but even with these you have to remember that some subjects like snow or a beach actually reflect more light than the camera is 'expecting' and thus take a picture that is too dark.

Another thing is that sometimes your chosen subject may be in front of a bright background. In these cases, your poor old camera may get a bit confused and set itself to capture the whole picture it sees thus capturing all incorrectly, the background being too light, while the subject, the thing you were trying to capture in the first place, is just too dark.

Keeping an eye on what the camera is doing