Anatomy of a camera - Camera Controls Cameras have number of controls that allow the user to change the way the photograph looks. Focus In the eye the cornea and the lens adjust the focus on the retina. This is done by varying the shape of the lens, the nearer the object in focus shorter and fatter the lens and vice versa. It is slightly different in a camera lens as it is made up of a number of individual lenses, so in cameras this is achieved by moving the lenses closer or further apart. Focus depths are expressed in distance up to infinity (lenses nearer the CCD). Focal length is worked out as the distance between where the cameras focal point is and the distance to the back of the plate or CCD. Shutter It isn t just the amount of light that is let into the camera that affects the image, but also for how long it s exposed for. This is controlled by the shutter which exposes the image for a period. Shutter speeds vary but are expressed in fractions of a second. Aperture The aperture allows light into the camera. The narrower the aperture the less light is allowed in. The greater the aperture the greater the light allowed. Aperture is expressed in F stops. Aperture is worked out as a ratio of the diameter f the aperture to the focal length of the lens. This is usually expressed as an F stop number which are standard to all cameras. (f1,f1.4,f2,f2.8,f4,f5.6,f8,f11,f16.) e.g. a 100mm lens with a setting of f4 would mean the opening of the iris is (100/4) 25mm. This means that f stops are relative to all lenses. This also means that aperture is either double or halves the exposure relative to the shutter speed. Increasing the shutter speed by one stop and decreasing the aperture by one stop will result in the same exposure.
Film Grain Why am I telling you about film when this is a digital camera module? The answer is simple. Photography is a science that has been around for well over 150 years. The Digital revolution has been around at most for 20 years. When the language of film is so old and all that is different is the way pictures are developed, stored and manipulated, then it is foolish just to concentrate on digital. The analogue process works by exposing light energy in a controlled way to light sensitive chemicals. This forms a latent image. The crystals of Silver bromide react to the energy from the light and conglomerate to form Silver atoms the latent image. It is then through the process of development that the sensitivity of the image is increased to form a picture and this is fixed to stop the process continuing. The film can have a number of properties such as the film speed. This is a representation of the graininess of the film as regards the crystals within the gelatine of the film strip. Larger grains expose to the light energy more quickly and so faster shots can be taken of objects moving at high speed. However this also leads to a grainy image. Film speed is expressed by an ISO (International Standards Organisation) number usually of 100-400; it is also interchangeable with the ASA number (American Standards Association) 100 being relatively slow 400 being fast. This is true for both colour and black and white films. Colour film has what is known as a Tri-Pack. Colour images as we have seen are made up of three wavelengths of light Red, Green and Blue. These are complimented by Yellow (Red Green x Blue), Magenta (Red Blue x Green), Cyan (Blue Green x Red) (the x indicates the colour blocked). Colour film is made up of three emulsions of Silver Bromide each sensitive to different wavelengths of light.
The CCD Today Digital cameras also split the reflected light into its constituent Red Green and Blue wavelengths. But this is converted into electrical signals by the CCD (Charge Couple Device) which converts one form of energy into the RGB constituents and then saves them on a storage media. Digital cameras have a rating which is in megapixels. Each manufacturer uses a different make up of specific CCD, some are better than others but all are jealously guarded in the way they specifically work. When choosing a digital camera it is easy to go with the thought that the greater number of pixels the better the resolution and the better the camera. This isn t strictly true. The resolution has to be divided into the area that the pixel inhabit this is given in a measurement of line pairs (r and g, b and g) per millimetre. In actuality the resolution effect of having more pixels on a chip is actually quite small (1.4x) and only quadruple the number of pixels doubles the resolution. Plus the other factors about the camera (lens size etc) affect the picture output to a higher degree. (so a 2 megapixel mobile phone will not outperform a 2 megapixel camera). The best advice is to take pictures and compare the output.
Depth of field With a pin hole camera the smaller the pinhole the sharper the picture, this makes sense, as a larger hole will let in more light and gradually as the hole gets bigger less of the image will be distinguishable. The phenomena of Depth of field is close to this, the aperture of the camera or the amount of light that is let into the camera means that the narrower the aperture (larger the f stop) the greater the focusing of more objects in the scene. This is known as Depth of field.
If for instance you are taking a photo of a long array of columns, and the camera is focused at the columns in the mid distance, the columns nearest the camera and those furthest away will be out of focus. This is especially noticeable in a wider aperture shot where fewer columns would be in focus. A good example of this is in a low light situation where the user could open up the aperture to let more light in. However by stopping up to a narrower aperture and increasing the exposure time you gain more depth of field and more columns will be in focus. The size of the lens also effects depth of field as lens focal length affects the aperture setting. For a larger lens the aperture must be larger to obtain the same exposure. Therefore with larger focal length lenses the depth of field is inherently less. Aperture Priority Shots taken at Aperture priority would be to obtain shots with a greater depth of field. The Aperture priority is when the user selects an aperture and lets the camera control the shutter speed to control the shots exposure (therefore prioritising the aperture). This is usually expressed as AP or A on modern cameras. Shutter Priority Shots taken with shutter priority is where the user sets the shutter speed and lets the camera set the aperture to control the exposure. An example of this is an action shot where the shutter speed has to be fast to capture quick moves. This is usually express as SP or S on most digital cameras. Exposure, Balancing & Metering Taking the correct exposure is essential to taking a good photo. It is a question of balancing the elements and maybe making a portion of the scene darker to make another lighter by comparison. In modern cameras this is usually worked out by the camera automatically taking a light reading and adjusting the exposure by controlling the aperture, shutter and filling in with a flash if necessary. But this does not frequently give good results. Usually this means that the user has to take meter readings and use sense and judgement to fill in. Usually this is achieved by half depressing the button and holding in to keep a setting for exposure for the point of interest.
Lenses We will be talking more about lenses soon but for now
The greater the focal length the more zoom the lens has. But the narrower the image. 200-600 mm lenses have a significant zooming in effect. 50mm is the standard lens which gives a good approximation of normal human vision with no distortions. And reduction in focal length results in a distorted image and a more wide-angle view ultimately culminating in the fish eye lens of a few millimetres.