Take Creative Control of Your Camera
I thought that I might start my blog by discussing the basics of how digital cameras works and why taking creative control of your camera is the first step to developing your skills as an amateur photographer. In this blog I’ll discuss aperture, shutter speed and ISO and how they combine to provide not only the correct exposure, but also to allow your creative vision to develop.
So where to start; well, digital cameras look very much like ordinary film cameras but they work in a completely different way. When you press the button to take a photograph with a digital camera, an aperture opens at the front of the camera and light streams in through the lens (ok, so this part hasn’t changed over the years so in truth all photography, be it film or digital, still relies on selecting the correct aperture and shutter speed to create correctly exposed images). The difference is how the image is stored and used. Obviously there is no film in a digital camera. Instead, there is a piece of electronic equipment that captures the incoming light rays and turns them into electrical signals. This light detector is called a charge-coupled device (CCD) or sensor.
In a digital camera, light reflected from the thing you are photographing zooms into the camera lens. This incoming light hits the CCD, which breaks it up into millions of pixels. The CCD measures the colour and brightness of each pixel and stores it as a number. Your digital photograph is effectively an enormously long string of numbers describing the exact details of each pixel it contains.
Once an image is stored in numeric form, you can do all kinds of things with it. Plug your digital camera into your computer, and you can download the images you've taken and load them into editing programs like Photoshop, or you can upload them onto websites, email them to friends, and so on. This is possible because your photographs are stored in digital format and all kinds of other digital gadgets use this digital format too.
If you open up a digital photograph in an image editing program, you can change it in all kinds of ways. This works by adjusting the numbers that represent each pixel of the image. So, if you click on a control that makes the image 20 percent brighter, the program goes through all the numbers for each pixel in turn and increases their brightness by 20 percent. What you see on the screen is the image changing as you edit or manipulate it, but what you don't see is the editing program changing all the numbers in the background.
Anyway, getting back to photography, I mentioned earlier that no matter whether you are shooting old school with film, or using the most modern digital camera, the thing that hasn’t changed is how the camera uses apertures and shutter speed to capture light and create the image, so perhaps it would make sense to know a little more about them.
The aperture is a small set of blades in the lens that controls how much light will enter the camera. The blades create an octagonal shape that can be widened or closed down. Obviously, if you shoot with the aperture wide open, then more light is allowed into the camera than if the aperture is closed down. Apertures are referred too using the letter f and a number, so on the camera or lens you will see f2.8, f4, f5.6, f8, f11,f16, f22 etc. It is common for people to assume a large number would mean a large hole, but actually it is the opposite, so f2.8 is a large hole, whilst f22 is a very small hole. This is probably the hardest thing for beginners to get their heads around but with time and experience, it starts to make sense.
When referring to an image, we often refer to two things, exposure and depth of field. Exposure is a term used to describe whether the image is too bright (over exposed), too dark (under exposed) or correctly exposed. In a correctly exposed image, there should be good definition in the dark areas of the image as well as in the light areas. This is sometimes tricky, especially in patchy, mottled light such as a rainforest, where sun streaming through the canopy makes for dark shadows and bright open areas, however one good thing about digital cameras is they allow us to review an image instantly, and see whether it is exposed correctly or not. The shot can then be retaken with the correct exposure.
Depth of field refers to how much of the image is in focus. A full depth of field means that everything in the image is in focus from flowers a few metres in front of the camera, to the mountain range in the distance, whereas a shallow depth of field means that only a small part of the image is in focus, whilst everything else is blurred. With practice a photographer can create an image with only a few inches (or less) in focus.
If you think of the shutter on your camera like a curtain on a window, then opening the curtain lets light in. If you open the curtain for a long time (slow shutter speed) you let lots of light in, but if you quickly open and close the curtain (fast shutter speed) only a small amount of light gets in. Shutter speeds range from very slow (30 seconds) to very fast 1/8000 of a second (or faster). Most cameras have a shutter speed referred to as BULB, which allows the shutter to remain open for longer periods. I often shoot star trails using a shutter speed of 30 minutes.
Generally speaking, slower shutter speeds (1/30th second or slower) are used to provide blur, such as the silky look you get when photographing a waterfall, whereas fast shutter speeds (1/400th second or faster) freeze the action, so that a racing car is in focus as it rushes past at 200km/h
ISO is an acronym, not that many people remember what it stands for. The sensitivity of digital camera sensors are rated using the ISO scale. ISO stands for the International Standards Organization, the people who define, among many other things, the specifications used to gauge light sensitivity. Anyway, importantly, the ISO controls exposure by using software in the camera to make it extra sensitive to light.
Putting this simply, ISO is the term used to describe how sensitive to light a sensor is. The lower the number, the less sensitive to light the sensor is. So how does this help you as a photographer, well, you can change the ISO on your digital camera whenever you like (in the old days of film, once you put a roll of 200 ISO film (or ASA as it was sometimes referred too) into as camera, you were stuck with it, and if the lighting conditions changed, you would need to change cameras, or film backs to get continue shooting. These days you can adjust the ISO on digital cameras after every shot. This is good because during bright daylight, you might want a low ISO (100 - 200), but if the light changes due to cloud cover or gong indoors, you might choose ISO 400 - 600, and during the night photographing stars you might choose ISO3200 or more to make the sensor extremely sensitive to light.
A high ISO such as ISO 2000 will produce a brighter picture than a lower ISO such as ISO 200. The drawback to increasing the ISO is that it makes the picture noisier. This noise is represented by tiny red spots on the image caused by pixels on the sensor heating up, and these will need to be removed, either by using a noise reduction algorithm in camera or during post processing. This may sound scary, but really it is not too difficult and I will discuss this in a later blog when I look at photographing stars
PUTTING IT ALL TOGETHER
Understanding how the combination of aperture, shutter speed and ISO affects an image is crucial, but more important is knowing what you wish to achieve in the photo. The first step when creating an image is to pre-visualise what you wish to achieve. Do you want blurred, silky water in a waterfall, or are you trying to freeze the movement and see every drop of water. Do you want a full depth of field where everything in the image from a metre in front of you to the distant mountains is in focus, or are you trying to isolate a flower by blurring out the background.
The way aperture, shutter speed and ISO interact decides how the image is exposed and what it looks like, but remember that changing any of these also changes the artistic ‘look’ of your image, for example, lowering the aperture size will let less light in, but it will also increase depth of field, increasing ISO will lighten the exposure, but it also increases noise, and adds ‘grain’ to an image, and increasing the shutter speed darkens the exposure, but also decreases the amount of ‘blurred movement’ in an image.
So in practice, if you are shooting a landscape and you want everything in focus, you need to achieve a full depth of field, this is done by shutting down the aperture to a small hole (usually f16 - f22), but remember that by doing this you are letting only a very small amount of light through onto the sensor, so you will need to compensate for this by letting this small amount of light in over a longer period to get correct exposure, or the image will be to dark. To achieve this, you need to use a slow (long) shutter speed, say one second, so you let a small amount of light in over a long time.
On the other hand, when photographing a flower, you may wish to blur the background so that the flower becomes the centre of attention, for this you want a shallow depth of field (a few inches), and to achieve this you need a let a lot of light onto the sensor (open up the aperture to f2.8 or f4). Again, if you let a lot of light in, you will easily over expose the image, so you need to compensate by adjusting the shutter speed to a fast speed (maybe 1/400 - 1/1000 second or faster) so you let a lot of light in quickly. Of course, this may be an issue if the flower is in a dark, shady corner of the garden and a fast shutter speed won’t allow enough light in. This can be sorted by bumping up the ISO in the cameras menu to say ISO1000
Finally you might be shooting a waterfall, and wish to create enough blurred movement in the water to create a silky appearance, to achieve this, you will require a long exposure, say two second, but you want a lot of the image in focus, and don’t want to over expose the image, so shooting with a small aperture, say f11 – f16 should provide the best outcome.
Well, I hope that made a little sense and might convince you to pick up your camera and get out there shooting. The only way to improve is practice.